Keithley 228A Service manual

Model 228AVoltage/Current Source

Instruction Manual

A GREATER MEASURE OF CONFIDENCE

WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of 1 year
from date of shipment.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable
batteries, diskettes, and documentation.

During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.

To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio.
You will be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service
facility. Repairs will be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for
the balance of the original warranty period, or at least 90 days.

LIMITATION OF WARRANTY

This warranty does not apply to defects resulting from product modification without Keithley’s express written consent, or
misuse of any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from
battery leakage, or problems arising from normal wear or failure to follow instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY
IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PRO­VIDED HEREIN ARE BUYER’S SOLE AND EXCLUSIVE REMEDIES.

NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT,
INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS
INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE
OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE, BUT ARE NOT LIM­ITED TO: COSTS OF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY
PERSON, OR DAMAGE TO PROPERTY.

Keithley Instruments, Inc.

Sales Offices: BELGIUM: Bergensesteenweg 709 • B-1600 Sint-Pieters-Leeuw • 02-363 00 40 • Fax: [phone]

CHINA: Yuan Chen Xin Building, Room 705 • 12 Yumin Road, Dewai, Madian • Beijing 100029 • 8610-6202-2886 • Fax: [phone]
FINLAND: Tietäjäntie 2 • 02130 Espoo • Phone: [phone] • Fax: [phone]
FRANCE: 3, allée des Garays • 91127 Palaiseau Cédex • 01-64 53 20 20 • Fax: [phone]
GERMANY: Landsberger Strasse 65 • 82110 Germering • 089/84 93 07-40 • Fax: [phone]
GREAT BRITAIN: Unit 2 Commerce Park, Brunel Road • Theale • Berkshire RG7 4AB • 0118 929 7500 • Fax: [phone]
INDIA: Flat 2B, Willocrissa • 14, Rest House Crescent • Bangalore 560 001 • 91-80-509-1320/21 • Fax: [phone]
ITALY: Viale San Gimignano, 38 • 20146 Milano • 02-48 39 16 01 • Fax: [phone]
KOREA: FL., URI Building • 2-14 Yangjae-Dong • Seocho-Gu, Seoul 137-130 • 82-2-574-7778 • Fax: [phone]
NETHERLANDS: Postbus 559 • 4200 AN Gorinchem • 0183-635333 • Fax: [phone]
SWEDEN: c/o Regus Business Centre • Frosundaviks Allé 15, 4tr • 169 70 Solna • 08-509 04 679 • Fax: [phone]
SWITZERLAND: Kriesbachstrasse 4 • 8600 Dübendorf • 01-821 94 44 • Fax: [phone]
TAIWAN: 1FL., 85 Po Ai Street • Hsinchu, Taiwan, R.O.C. • 886-3-572-9077 • Fax: [phone]

28775 Aurora Road • Cleveland, Ohio 44139 • 440-248-0400 • Fax: [phone]

1-888-KEITHLEY (534-8453) • www.keithley.com

© Copyright 2001 Keithley Instruments, Inc.

Printed in the U.S.A.

11/01

Model 228A Voltage/Current Source

Instruction Manual

All references to the Model 228 apply also to the Model 228A.

©1988, Keithley Instruments, Inc.

All rights reserved.

Cleveland, Ohio, U.S.A.

Fifth Printing, December 2000

Document Number: 228A-901-01 Rev. E

Safety Precautions

The following safety precautions should be observed before using
this product and any associated instrumentation. Although some in­struments and accessories would normally be used with non-haz­ardous voltages, there are situations where hazardous conditions
may be present.

This product is intended for use by qualified personnel who recog­nize shock hazards and are familiar with the safety precautions re­quired to avoid possible injury. Read and follow all installation,
operation, and maintenance information carefully before using the
product. Refer to the manual for complete product specifications.

If the product is used in a manner not specified, the protection pro­vided by the product may be impaired.

The types of product users are:

Responsible body is the individual or group responsible for the use

and maintenance of equipment, for ensuring that the equipment is
operated within its specifications and operating limits, and for en­suring that operators are adequately trained.

Operators use the product for its intended function. They must be

trained in electrical safety procedures and proper use of the instru­ment. They must be protected from electric shock and contact with
hazardous live circuits.

Maintenance personnel perform routine procedures on the product

to keep it operating properly, for example, setting the line voltage
or replacing consumable materials. Maintenance procedures are de­scribed in the manual. The procedures explicitly state if the operator
may perform them. Otherwise, they should be performed only by
service personnel.

Service personnel are trained to work on live circuits, and perform

safe installations and repairs of products. Only properly trained ser­vice personnel may perform installation and service procedures.

Keithley products are designed for use with electrical signals that
are rated Installation Category I and Installation Category II, as de­scribed in the International Electrotechnical Commission (IEC)
Standard IEC 60664. Most measurement, control, and data I/O sig­nals are Installation Category I and must not be directly connected
to mains voltage or to voltage sources with high transient over-volt­ages. Installation Category II connections require protection for
high transient over-voltages often associated with local AC mains
connections. Assume all measurement, control, and data I/O con­nections are for connection to Category I sources unless otherwise
marked or described in the Manual.

Exercise extreme caution when a shock hazard is present. Lethal
voltage may be present on cable connector jacks or test fixtures. The
American National Standards Institute (ANSI) states that a shock
hazard exists when voltage levels greater than 30V RMS, 42.4V
peak, or 60VDC are present. A good safety practice is to expect

that hazardous voltage is present in any unknown circuit before
measuring.

Operators of this product must be protected from electric shock at
all times. The responsible body must ensure that operators are pre­vented access and/or insulated from every connection point. In
some cases, connections must be exposed to potential human con­tact. Product operators in these circumstances must be trained to
protect themselves from the risk of electric shock. If the circuit is
capable of operating at or above 1000 volts, no conductive part of

the circuit may be exposed.

Do not connect switching cards directly to unlimited power circuits.
They are intended to be used with impedance limited sources.
NEVER connect switching cards directly to AC mains. When con­necting sources to switching cards, install protective devices to lim­it fault current and voltage to the card.

Before operating an instrument, make sure the line cord is connect­ed to a properly grounded power receptacle. Inspect the connecting
cables, test leads, and jumpers for possible wear, cracks, or breaks
before each use.

When installing equipment where access to the main power cord is
restricted, such as rack mounting, a separate main input power dis­connect device must be provided, in close proximity to the equip­ment and within easy reach of the operator.

For maximum safety, do not touch the product, test cables, or any
other instruments while power is applied to the circuit under test.
ALWAYS remove power from the entire test system and discharge
any capacitors before: connecting or disconnecting cables or jump­ers, installing or removing switching cards, or making internal
changes, such as installing or removing jumpers.

Do not touch any object that could provide a current path to the com­mon side of the circuit under test or power line (earth) ground. Always
make measurements with dry hands while standing on a dry, insulated
surface capable of withstanding the voltage being measured.

The instrument and accessories must be used in accordance with its
specifications and operating instructions or the safety of the equip­ment may be impaired.

Do not exceed the maximum signal levels of the instruments and ac­cessories, as defined in the specifications and operating informa­tion, and as shown on the instrument or test fixture panels, or
switching card.

When fuses are used in a product, replace with same type and rating
for continued protection against fire hazard.

Chassis connections must only be used as shield connections for
measuring circuits, NOT as safety earth ground connections.

If you are using a test fixture, keep the lid closed while power is ap­plied to the device under test. Safe operation requires the use of a
lid interlock.

If a screw is present, connect it to safety earth ground using the
wire recommended in the user documentation.

!

The symbol on an instrument indicates that the user should re­fer to the operating instructions located in the manual.

The symbol on an instrument shows that it can source or mea­sure 1000 volts or more, including the combined effect of normal
and common mode voltages. Use standard safety precautions to
avoid personal contact with these voltages.

The WARNING heading in a manual explains dangers that might
result in personal injury or death. Always read the associated infor­mation very carefully before performing the indicated procedure.

The CAUTION heading in a manual explains hazards that could
damage the instrument. Such damage may invalidate the warranty.

Instrumentation and accessories shall not be connected to humans.

Before performing any maintenance, disconnect the line cord and
all test cables.

To maintain protection from electric shock and fire, replacement
components in mains circuits, including the power transformer, test
leads, and input jacks, must be purchased from Keithley Instru­ments. Standard fuses, with applicable national safety approvals,
may be used if the rating and type are the same. Other components
that are not safety related may be purchased from other suppliers as
long as they are equivalent to the original component. (Note that se­lected parts should be purchased only through Keithley Instruments
to maintain accuracy and functionality of the product.) If you are
unsure about the applicability of a replacement component, call a
Keithley Instruments office for information.

To clean an instrument, use a damp cloth or mild, water based
cleaner. Clean the exterior of the instrument only. Do not apply
cleaner directly to the instrument or allow liquids to enter or spill
on the instrument. Products that consist of a circuit board with no
case or chassis (e.g., data acquisition board for installation into a
computer) should never require cleaning if handled according to in­structions. If the board becomes contaminated and operation is af­fected, the board should be returned to the factory for proper
cleaning/servicing.

11/01

SPECIFICATIONS

AS A CONSTANT VOLTAGE SOURCE

RANGE OUTPUT

MAXI- RESO- (1 YEAR)

MIJMLUnON

ACCURACY’ ACCURACY

184-28T

loOV rtlol.oV lC&nV ~t(O.l%+O.l V) k1.010 A lm.4 *(O.l%+ 4mA)

1OV ztlo.loV 1omV rt(O.l%+ 1omV) 3~10.10 A lomA rt(O.5%+ 4omA)

IV +l.OlOV ImV zt(O.l%+l.OmV) k10.10 A 1OmA ct(O.%%+ 4omA)

l

AboveO.4% range.

TEMPERATURE COEFFICIENT (OO-lS°C & 28”-50’0: +(O.l X apphc-

able accuracy specification)/°C.

NOISE: RANGE

OUTPUT RESISTANCE

1V Range: 100 PO.

lOOV

1ov

1V

0.1-3OOHz O.l-3OOkHz

5.omv p-p

2.OmV p-p 15mV p-p

0.7mV p-p

(max.):

1OOV Range: 1OmI-l. 1OV Range: 100 ~0

OUTPUT INDUCTANCE: lC+H typical.
SENSING: Rear panel switch selectable REMOTE and LOCAL sensing.
REMOTE SENSING: Corrects for up to OSV drop per output lead. Max-

imum 50 per sense lead for rated accuracy. Maximum 0.53 per sense lead

for rated output resistance.

COMPLIANCE (Source or Sink)

MAXI-

fO.lOlOA 100 pA f(0.1%+400 PAI

rt1.010 A 1mA k(O.l%+ 4mA)
+O.lOlOA 100 PA f(0.1%+400 pA)

3~1.010 A 1mA k(O.l%+ 4mA)
fO.lOlOA 100 pI rt(O.l%++400pA)

RESO (1YEAR)

MUM LUnON 180~2ST

0.1~20MHz

15mV p-p
15mV p-p

25mV p-p typ.

25mV

p-p typ.

25mV p-p typ.

AS A CONSTANT CURRENT SOURCE

RANGE OUTPUT (1 YR., 18”-28’C)

ACCURACY’ ACCURACY

MAXI- RESO

MlJTvI LUTION

10 A 3~10.10 A lOmA *(OS%+ lomA) 3zlO.lOV 1OmV +(O.l%+ 4OmV)

1 A +l.OlO A 1mA +(O.l%+l.OmA) flOl.OV 1CGmV ~t(O.l%+4OomV)

O.lA tO.lOlOA 100 pA +(0.1%+0.111~4)

(1 YEAR) MAXI- RE50- (1 YEAR)

IS”-28T

*Above 0.4% of range.

TEMPERATURE COEFFICIENT (O”-18°C 6~ 28”-50°C): +(O.l Xappiic-

able accuracy specification)/OC.

NOISE: RANGE

OUTPUT RESISTANCE (min.): 10A Range: 109. 1A Range: l&R. O.lA

Range: 109

10 A

1 A
O.lA

O.l-3OOHz

2.5 mA p-p 25mA p-p
5 mA P-P

OSmA p-p

OUTPUT CAPACITANCE: 0.2rF typical.
OUTPUT LOAD: Must be non-inductive.

COMPLIANCE (Source or Sink)

MUM LUTION

fl.OlOV

flO.lOV Khnv *(o.l%+ 4omV)
fl.OlOV

flOl.OV
*10.1ov

*1.01ov 1mV *(O.l%+ 4mV)

1mv f(o.l%+ 4mV)

1mv *(o.l%+ 4mV)

1WmV

1Omv zt(O.l%b 4omV)

la=28x

rt(O.l%+4OOmV)

O.l-3OOkHz O.l-20MHz

P-P

S-l-IA P-P typ.
mnL4 P-P typ.

3mA P-P typ.

5nL4 P-P

2m.4

CURRENT MONITOR OUTPUT

SCALE FACTOR: 1V =i 100% of range.
ACCURACY: Same as constant current mode.
BANDWIDTH: 5kHz typical.
OUTPUT RESISTANCE: 1okR.

EXTERNAL MODULATION

INPUT RESISTANCE: &SKI .
SENSITIVITY: - 1OV increases magnitude of programmed output by

100% of full scale; + 1OV decreases magnitude of programmed output by

100% of full scale.
ACCURACY: 2% typical, dc to 6OHz.
MAXIMUM MODULATION: Modulation and programmed settin

not cause operation exceeding the range of zero to 101% of fui

should

‘i scale.

MODULATION FREQUENCY: 6OOHz bandwidth.

IEEE-488 BUS IMPLEMENTATIoN (IElZE-48&1978)

M;I.;IL;;; COMMANDS: DCL, LLO, SDC, GET, GTL, UNT, UNL,
UNILINE COMMANDS: IFC, REN, EOI, SRQ, ATN.

INTERFACE FUNCTIONS: SHl, AHl, Tb, TEtJ, L4, LEO, SRI, RLl, PPO,

DCl. DTl. CO. El.
PROGRAMMABLE PARAMETERS: Output (operate or standby), Range,

Voltage, Current, Trigger Mode, Sink, Modulation (Voltage or Current),

Display Mode, Output Prefix (data format on readback), SRQ Mask,

EOI, Terminator Characters, Status, Self Test, Memory Location (100

point memory), Dwell Time.

GENERAL

DISPLAY: Dual 3i/,-digit LED (0.5 in.) indicate programmed values in

Standby and output values in Operate.
READBACK ACCURACY: Same as output accuracy.
FRONT PANEL PROGRAMS: COPY, SINK, IEEE address, MOD V,

MOD I, TEST, RESET.

LOAD TRANSIENT RECOVERY TIME: With a resistive load the output

will recover 90% of any load changes within Ims after end of changes,

provided the changes do not cause transfer to another control mode.

STANDBY: Programs ourput to OV, OA without changing ranges or polarity.
LINE REGULATION: Less than 0.01% output change for ac power line

changes within specified limits.
PROGRAM MEMORY (battery backed

tings. Range of Dwell Times: lOms to 1000s. Accuracy of Dwell Times:
*(O.O5%+2ms).

BATTERY BACKUP: Rechargeable 3.6V nickel-cadmium. 1 month reten-

tion of data with unit turned off.

TRIGGER: IN and OUT ‘I-IL-compatible.

PROGRAMMING RESPONSE TIME: Less than 1OOms on fixed range

(typical).

MAXIMUM

chassis): 1OOV dc.

COMMON

MODE VOLTAGE (output or output

OUTPUT CONNECTIONS: Quick disconnect card with screw terminals

for output, modulation, current monitor, and external sense. BNC

(chassis isolated) connectors for TRIGGER IN/OUT.

SELF TEST: Analog and digital circuits tested at power-on. Power sup-

plies, temperatures, and output continuously monitored.

WARMUP: 10 minutes to rated accuracy.
POWER: 10.5-125 or 210-250 V ac (internally switch selectable), 50 or

60Hz, 500 VA maximum.

COOLING: Internal fan for forced air cooling.
ENVIRONMENT:

RH below 35°C.

DIMENSIONS, WEIGHT: 133mm high X 435mm wide X 448mm deep

(51/r in. X 17% in. X 1736 in.). Net weight 10.9kg (24 Ibs.).

ACCESSORIES AVAILABLE:

Model 2288:

Model 2289:

Model 7008-3: IEEE-488 Cable (3 ft.)

Model 7008-6: IEEE-488 Cable (6 ft.)

Operating: 0”

Storage: -25“ to 70°C.

Fixed Rack Mounting Kit
Slide Rack Mounting Kit

up):

Stores up to 100 output set-

common to

to 50°C. less than 80% non-condensing

TABLE OF CONTENTS

SECTION 1 — GENERAL INFORMATION

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.3 Using the Instruction Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.4 Warranty Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.5 Manual Addenda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.6 Safety Symbols and Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.7 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.8 Unpacking and Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.9 Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

SECTION 2 — SAFETY AND GENERAL OPERATION

2.1 Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.2 General Operating Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.3 General Operation Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.4 Standby Mode Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

SECTION 3 — FRONT PANEL OPERATION

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.2 Preparation For Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.2.1 Line Voltage Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.2.2 Fuse Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.3 Power Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.4 Warm Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3.5 Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3.6 Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3.7 Front Panel Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7

3.8 Rear Panel Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

3.9 Quick Disconnect Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

3.10 Remote/Local Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.11 Front Panel Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.11.1 Program 1 Copy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.11.2 Program 2 Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19

3.11.3 Program 3 IEEE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19

3.11.4 Program 4 MOD V (Modulate Output Voltage) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

3.11.5 Program 5 MOD I (Modulate Output Current) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

3.11.6 Program 6 Test (Diagnostic Self Test) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

3.11.7 Program 9 Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

3.12 Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

3.12.1 Load Line Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22

3.12.2 Resistive Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

3.12.3 Reactive Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

3.12.4 Inductive Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

3.12.5 Capacitance Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26

3.12.6 Load Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26

3.12.7 Charging and Discharging Electrochemical Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

3.13 Operating Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

3.13.1 Example 1: 10.00V, 10.00A Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

3.13.2 Example 2: 100V, 1A Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-29

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3.13.3 Example 3: 1V, 10A, 1sec; 10V, 10A 2sec; and 100V, 1A, 3sec Output in the

Continuous Memory Control Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

3.13.4 Example 4: Model 228 as an Active Load (Current Sink) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33

3.13.5 Example 5: Operation as Source and Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35

3.13.6 Example 6: Fabricating Output Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35

3.13.7 Example 7: Using the External Trigger (Input and Output) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-36

3.13.8 Example 8: Floating Operation (Extended Compliance) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37

3.14 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37

3.14.1 Low Resistance Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37

3.14.2 Battery Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-38

3.14.3 External Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-39

3.14.4 Ramp Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40

3.14.5 Power Semiconductor Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-41

3.14.6 Compensation for Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-43

SECTION 4 — IEEE BUS OPERATION

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.1.1 Software Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.1.2 Interface BASIC Programming Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.1.3 Interface Function Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.1.4 Model 228 Interface Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.2 IEEE-488 Bus Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.2.1 Bus Management Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.2.2 Handshake Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.2.3 Data Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.3 System Set Up Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.4 Bus Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4.4.1 Uniline Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.4.2 Universal Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.4.3 Addressed Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

4.5 Device-Dependent Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

4.5.1 Display Mode (D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

4.5.2 Memory Control Mode (P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16

4.5.3 Prefix (G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

4.5.4 SRQ Response Mode (M) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19

4.5.5 Trigger Modes (T) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21

4.5.6 Programmable Terminator (Y) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21

4.5.7 Inputs (I, V, W and B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-22

4.5.8 Function (F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-24

4.5.9 Range (R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-24

4.5.10 External Modulation (A, C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26

4.5.11 Sink Mode (S) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26

4.5.12 Status Word (U) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26

4.5.13 Self Test (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28

4.5.14 EOI and Bus Hold-Off Modes (K) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28

4.6 Front Panel Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

4.6.1 IDDC Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30

4.6.2 IDDCO Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30

4.6.3 No Remote Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30

4.7 Response Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-31

SECTION 5 — PERFORMANCE VERIFICATION

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.2 Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

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5.3 Recommended Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.4 Initial Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.5 Performance Verification Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.5.1 Voltage Mode Verification (1V, 10V and 100V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.5.2 Output Current Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

SECTION 6 — THEORY OF OPERATION

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.2 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.2.1 Linear Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.2.2 Switching Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

6.3 Analog Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

6.4 Digital Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

6.5 Display Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

SECTION 7 — MAINTENANCE

7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.2 Fuse Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.3 Line Voltage Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.4 Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7.4.1 Removing the Top and Bottom Covers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7.4.2 Remove the Rear Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7.4.3 Digital Board, Mother Board and Power Supply Board Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7.4.4 Heat Sink Assembly and Fan Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7.5 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7.5.1 Recommended Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7.5.2 Digital Self Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7.5.3 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7.6 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

7.6.1 Recommended Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

7.6.2 Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

7.6.3 Warm Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

7.6.4 Top Cover Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

7.6.5 +15V Supply Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

7.6.6 Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

7.6.7 +1V Reference Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

7.6.8 Current Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

7.7 Special Handling of Static Sensitive Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-18

SECTION 8 — REPLACEABLE PARTS

8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.2 Replaceable Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.3 Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.4 Factory Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.5 Schematic Diagrams and Component Location Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

iii

iv

LIST OF ILLUSTRATIONS

3-1 Graph of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3-2 Model 228 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

3-3 Model 228 Rear Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

3-4 Quick Disconnect Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

3-5 Quick Disconnect Board Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

3-6 Graph of Operation for External Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

3-7 Load Line (Positive Line Shown) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-23

3-8 Resistive Load Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

3-9 Limiting Inductive Reaction Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

3-10 Inductive Load Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26

3-11 Capacitive Load Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26

3-12 Model 228 Recommended Operating Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34

3-13 Model 228 as an Active Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34

3-14 Output Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-36

3-15 External Trigger Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37

3-16 Connection for Floating Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37

3-17 Low Resistance Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-38

3-18 Battery Life Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-39

3-19 Data Logging Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-39

3-20 Power Supply Protection Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-39

3-21 Connections for External Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40

3-22 Typical Modulated Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40

3-23 Ramp Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40

3-24 Ramp Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-41

3-25 Power Transistor Test Set up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-41

3-26 Power Transistor I

3-27 Automated Test Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-42

3-28 FET Test Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-42

3-29 FET Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-42

3-30 Automated Test Set Up for FETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-43

/V

Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-42

C

CE

4-1 Bus Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4-2 Handshake Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4-3 Contact Assignments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4-4 Typical Bus Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4-5 Format of SRQ Mask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19

4-6 Format of SRQ Status Byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19

4-7 Error Status Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-27

4-8 Status Word Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-27

4-9 IEEE Display Error Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

5-1 Output Voltage Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5-2 Output Current Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

6-1 Model 228 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6-2 Analog Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6-3 A/D Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6-4 Voltage Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

6-5 Current Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

6-6 Output Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

6-7 Display and Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

v

7-1 Top and Bottom Cover Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

7-2A Rear Panel Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

7-2B Wiring Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

7-3 Model 228 Exploded View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

7-4 Detail of Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7-5 Heat Sink Assembly (Exploded View) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7-6 Calibration Setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

8-1 Mother Board, Component Location Drawing, Dwg. No 228-100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6

8-2 Mother Board, Schematic Diagram, Dwg. No. 228-106 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7

8-3 Display Board, Component Location Drawing, Dwg. No. 228-110 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15

8-4 Display Board, Schematic Diagram, Dwg. No. 228-116 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17

8-5 Power Supply Board, Component Location Drawing, Dwg. No. 228-150 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22

8-6 Power Supply Board, Schematic Diagram, Dwg. No. 228-156 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23

8-7 Digital Board, Component Location Drawing, Dwg. No. 228-140 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-27

8-8 Digital Board, Schematic Diagram, Dwg. No. 228-146 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29

vi

LIST OF TABLES

3-1 Line Voltage Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3-2 Front Panel Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

3-3 Rear Panel Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3-4 Front Panel Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8

3-5 Front Panel Messages and Prompts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

3-6 Error Messages (Either Display) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

3-7 Power up Default Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

3-8 Summary of Front Panel Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3-9 Maximum Inductive Reaction Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26

4-1 HP-85 and IBM BASIC Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4-2 Model 228 Interface Function Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4-3 IEEE Command Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4-4 IEEE Contact Designations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4-5 DCL and SDC Default Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

4-6 Device-Dependent Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

4-7 Device-Dependent Commands Not Available to the Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4-8 Hierarchy of Command Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

4-9 SRQ Mask Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19

4-10 Input Command Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-22

4-11 Range Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-24

4-12 Hold Off Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

4-13 Response Time (Voltage Changes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-31

4-14 Response Times (Other Control Changes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-31

5-1 Recommended Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5-2 Output Voltage Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5-3 Output Current Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

7-1 Fuse Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7-2 Low Voltage Operation Part Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7-3 Line Voltage Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7-4 Recommended Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7-5 Power Supply Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14

7-6 Analog Circuitry Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14

7-7 Digital Circuitry Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7-8 Display Board Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

7-9 Recommended Calibration Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

7-10 Model 228 Static Sensitive Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-18

8-1 Mother Board Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

8-2 Display Board Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13

8-3 Power Supply Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19

8-4 Digital Board Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-25

8-5 Mechanical Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-33

vii

viii

SECTION I

GENERAL INFORMATION

1.1 INTRODUCTION

The Model 228 Voltage/Current Source is both a constant
voltage and constant current source with front panel and
IEEE operation. The Model 228 can be used as a constant
voltage source or a constant current source. It has four
quadrant operation. This means that the voltage or current
sources can operate as a source or a sink in either positive or
negative polarities. Full power capability of 1OOW may be ob­tained in any quadrant.

Parameter entry is done in one of two ways. Either using the
data keypad to enter the desired value into the display or us­ing the display modify function. The display modify function
allows the user to modify either display by selecting a digit of
the display and incrementing or decrementing that digit with
the appropriate keys. With the carry, borrow and autorepeat
capability, front panel operation is flexible and easy to pro­gram. The user selects the range with the decimal point.

The Model 228 has a 100 point data memory that allows the
user to store up to 100 unique values of current, voltage and
dwell time for future use. Once a particular level is stored in
the data memory, the user need not reprogram that level.

The output terminals are located on a quick disconnect board

that inserts into the rear panel of the mainframe. The output
is disconnected from the quick disconnect board when it is
removed from the mainframe.

1.2 FEATURES

The Model 228 includes the following features:

l Six ranges that allow a wide variety of voltage/current

values.

l Seven front panel programs. The programs include:

Program 1 Copy for duplicating memory location informa-

tion.
Program 2 Sink for sink only operation.
Program 3 IEEE for changing IEEE primary address.
Program 4 MOD V for modulating output voltage.
Program 5 MOD 1 for modulating output current.
Program 6 Test for Model 228 self test.
Program 9 Reset for resetting the Model 228 to factory set
values. See paragraph 3.13.7

l Dual displays for easy reference of the instrument’s status.

The left display has two display modes (voltage and mem-

ory step). The right display also has two display modes

amps and seconds).

l Two methods of modifying the source or sink value: Data

entry from the data keypad, and increment or decrement of

displayed valued using the decade keys.

l 100 point data memory to store up to 100 unique values of

voltage, current and dwell time. Each location also includes:

sink mode status and voltage current modulation status.

All information stored in a memory location is battery
backed up. This means that if the instrument is powered
down, the stored information (voltage, current and dwell

time parameters) remains in a particular location until

changed by the user.

l OPERATE/STANDBY switch that places the output in

either the operate mode (displayed value is present at out­put) or in the standby mode (output is programmed to ap­proximately zero).

l Compliance status is easy to read on the front panel com-

pliance graph. The graph shows the user at a glance how the
Model 228 is operating (source or sink polarity and voltage

or current compliance).

l IEEE-488 bus operation is standard. This enables the Model

228 to be incorporated into a system that uses programmed

control over the IEEE-488 bus.

l Single step, single cycle and continuous memory modes

control the sequence between data points in the 100 point

data memory. The program mode may be controlled in one
of three ways; using the front panel START/STOP key, the

external trigger pulse or by commands over the IEEE-488
bus.

l Output terminals are located on the quick disconnect board

for optimum safety. The output terminals, the sense ter-

minals, current monitor terminals and the external modula-

tion terminals are also located on the quick disconnect
board. Several quick disconnect boards may be wired with
their own unique wiring ‘configuration. When one configur­ation is required, simply insert into the mainframe. In this
way, cumbersome rewiring of one board is avoided.

l Remote and Local Sensing. This allows the user to sense at

the output terminals or at the load or source. Remote sens-

ing compensates for the effects of the l*R lead drop by
maintaining regulation at the load instead of at the output
terminals of the Model 228.

l Four Q,uadrant Operation. This means that the voltage or

current outputs can operate as a source or a load in either
positive or negative polarities. The front panel compliance

graph shows the user where the Model 228 is operating

(source or sink).

1-l

l Output Modulation. This feature allows the output signal

to be modulated from an external AC signal source. Voltage

or current may be modulated.

l Bipolar Output. This means that the polarity of the output

may be reversed by using front panel controls instead of

reversing the wires.

l Most of the front panel keys autorepeat if held in.

1.5 MANUAL ADDENDA

Information concerning improvements or changes to the in­strument which occur after the printing of this manual may
be found on an addendum sheet included with this manual.
Be sure to review these changes before attempting to operate
the instrument.

1.3 USING THE INSTRUCTION MANUAL

This manual contains information necessary for operating,
programming and servicing the Model 228 Voltage/Current

Source and is divided into the following sections:

Section 2 contains safety instructions and a general

1.
operating procedure.

2.

Section 3 contains front and rear panel descriptions, a
general operating procedure and specific operating ex­amples showing how to use the Model

3.

Section 4 contains information pertaining to the IEEE-488
bus, including primary address selection, device­dependent command programming, bus connection and
several sample programs.

4.

Section s includes a procedure to verify the performance
of the Model

5.

Section 6 contains theory of operation with detailed

228.

schematics and block diagrams. This section facilitates
understanding of the individual circuits of the Model 228.

6.

Section 7 contains servicing information for the Model

228. Calibration, troubleshooting, line voltage selection,
fuse replacement and static sensitive device information is
contained in this section.

7.

Section 8 gives replaceable parts information.

228.

If an additional manual is required, order the manual package
(Keithley Part Number 228-901-00). The manual package in­cludes an instruction manual and all pertinent addenda.

SAFETY SYMBOLS AND TERMS

1.6

following safety symbols and terms are used in this

The
manual or found on the Model 228:

The symbol !

on the instrument indicates that the user

A

--

should refer to the operating instructions in this manual.
The symbol

on the instrument indicates that a lethal

w
potential may be present at the output terminals. Standard
safety practices should be observed when such potentials are
encountered.

The

WARNING

heading used in this manual explains dangers

that could result in personal injury or death.
The

CAUTION

heading used in this manual explains hazards

that could damage the instrument.

1.7 SPECIFICATIONS

1.4 WARRANTY INFORMATION

Warranty information may be found inside the front cover of
this manual. Should it become necessary to exercise the war­ranty, contact your nearest Keithley representative or the fac­tory to determine the course of action. Keithley Instruments
maintains service facilities in the United States, United
Kingdom and throughout Europe. Addresses of these facilities
may be found inside the front cover of this manual. Informa­tion concerning the application, operation or service of your
instrument may be directed to the application engineer at any
of these locations.

1-2

Detailed Model 228 specifications may be found immediately
preceding this section of the manual.

1.8 UNPACKING AND INSPECTION

The Model 228 Voltage/Current Source was carefully in­spected, both electrically and mechanically before shipment.
Upon receiving the Model 228, carefully unpack all items
from the shipping containers and check for any obvious signs
for physical damage that may have occurred during ship-

ment. Report any damage to the shipping agent immediately.
Retain the original packing materials in case reshipment
becomes necessary. The following items are included with
every Model 228 order:

Model 228 Voltage/Current Source
Model 228 Instruction Manual, Reference and Program In-

structions and the Instruction Label.
Quick Disconnect Board
Additional accessories as ordered.

With all of the terminals on the board, many configurations could
be wired. To avoid cumbersome and time consuming rewiring
for each configuration, several quick disconnect boards could be
wired for each unique configuration. One quick disconnect board
is supplied with each Mode1 228.

Model 2288 Fixed Rack Mount- The Model 2288 is a fixed or

stationary rack mounting kit that mounts the Model 228 in a
standard 19 inch rack.

1.9 ACCESSORIES

Model 2286 Quick Disconnect Board - The quick disconnect
board contains output, sense, external modulation and current
monitor terminals. The quick disconnect board inserts into the
rear panel of the Model 228 mainframe. When the board is in
place, the terminals are connected to the actual potentials (if in
the operate mode). Removing the board from the mainframe
disconnects the terminals from the output. This is a safety feature
designed so the user should not have to come into contact with
a dangerous potential.

Model 2289 Slide Rack Mount- The Model 2289 is a sliding

rack mount kit. It enables one Model 228 to be rack mounted
with the added feature of sliding the instrument for fast ac­cess.

Model 7008-3-The Model 7008-3 is a 1 meter (3 feet)

IEEE-488 cable. The cable has 24 stranded wire conductors
and is terminated on each end with standard IEEE-488 con­nectors.

Model 7008-6-The Model 7008-6 is a 2 meter (6 feet)

IEEE-488 cable. The cable has 24 stranded wire conductors
and is terminated on each end with standard IEEE-488 con­nectors.

l-3/14

SECTION 2

SAFETY AND GENERAL OPERATION

2.1 SAFETY PRECAUTIONS

Safety information such as warnings and cautions are located
throughout this manual. The information is placed in the
appropriate places in the manual where a hazard may exist.
The warnings refer to a potentially dangerous situation
where personal injury or even death may occur. The cautions
refer to a potentially hazardous situation where the instru­ment may be damaged. Take the time to read and most of all
understand these warnings and cautions.

The following safety information is provided as a general
safety practice before, during and after operation of the
Model 228.

1. Do not operate the instrument with the top cover and/or
bottom cover removed. Lethal potentials are present
throughout the mainframe. The covers must also be in
place to allow proper air flow through the instrument.
Proper air flow is required to cool the instrument during
operation. If proper cooling is impeded the instrument
may overheat.

2. Never assume the output is at a safe potential while the
AC line is connected.

3. The Model 228 is capable of producing several times its
current rating for short periods of time (msec). Keep this
in mind when choosing a load. Brief bursts of high cur­rent are still enough to damage other instrumentation
and cause serious injury.

4. Using the Model 228 to sink power from an external
source requires some precautions that are outlined as
follows:

A. A temporary loss of line voltage resets the Model 228

output to a high impedance state. Therefore, a user
supplied voltage limiting circuit may be required to
control the external source. A zener diode placed
across the output is recommended.

B. When the voltage polarity of an external source

opposes the programmed polarity of the Model 228,
voltage has priority.

where:
V

= Source Voltage (V

S

= Source Current (I

I

S

= Load Resistance

R

L

when:
V

+ V

S

228

R

L

is greater than the current setting of the
Model 228.

SOURCE

SOURCE

)

)

The standby mode programs the Model 228 for
approximately 0.0V, 0.0A.

V

+ V

= V

= V

S

S

+ 0

is greater than zero.

L

/R

up to the limits of the output

S

L

S

228

R

R

L

Therefore, I
fuse. The output fuse is factory rated at 20A. In some

circuit applications it may be necessary to limit the
current with a resistor or select a lower rated output
fuse. The output fuse must have a minimum voltage
rating of 250V.

C. When the voltage polarity of an external source

matches the programmed polarity of the Model 228,
current has priority.

when:
V

— I

R

S

is greater than the voltage setting of

S

L

Model 228.

D. After using the Model 228 to charge a storage ele-

ment, such as an electrochemical cell or capacitor,
NEVER change the polarity of the source to dis­charge the cell. Doing so will damage the Model 228.
ALWAYS allow the cell to completely discharge
before changing the source polarity to charge it in
the opposite direction. The cell can be safely dis­charged with the source set to 0V. See paragraph

3.12.7 for details.

5. Before operation, ground the instrument through a prop­erly earth grounded receptacle. Failure to ground the
instrument may result in severe injury or even death in
the event of a short circuit or malfunction.

6. After extensive use of the Model 228, set the instrument
to standby and allow it to cool down for a few minutes
before turning off the power to the instrument.

7. Never come into contact with the output connections
while the instrument is turned on.

8. Observe proper polarity when operating in the sink
mode. A reversed polarity may allow the instrument to
operate at a current limit of the output fuse.

9. Use cables for the output that have appropriate current
and insulation rating. For example, if 10V at l0A is to be
produced or dissipated then the cables must be rated for
that amount. Also, use insulated lugs for connections on
the quick disconnect board.

10. Do not leave the instrument unattended when it is in the
operate mode. Always place the instrument in standby
after the measurement or test is completed.

11. Always set up the test circuit while the power is turned
off. Do not come into contact with any part of the test cir­cuit while power is on.

2-1

2.2 GENERAL OPERATING PROCEDURE

This is a general operating procedure to familiarize the user
with front panel operation of the Model 228. There are sev­eral operating parameters involved with Model 228 opera­tion. These parameters are taken into account in this
procedure. Of course, every detail of Model 228 operation is
not covered in the general procedure. Section 3 includes sev­eral specific examples of Model 228 operation.

NOTE

Most of the front panel keys auto-repeat if held
in. Refer to the operation notes at the end of this
procedure.

1. Turn on the Model 228 and allow 10 minutes for warm­up.

NOTE

To achieve rated accuracy, run Program 6 imme­diately after the 10-minute warm-up period.

2. Select the desired memory location. There are two meth­ods for selecting memory locations. This procedure cov­ers both methods.

NOTE

The unit powers up to memory location 1. This
need not be changed if memory control is not
being used.

Method 1: Select Memory Location

A. Press the VOLTS/MEMORY STEP key if not in the

memory step display. The present memory location
is displayed on the left display.

B. Press the SELECT key to select the display to be

modified (left or right). The selected display is indi­cated by the flashing bright digit.

C. Press the left or right key (indicated by the left and

right arrows) to select the digit that is to be modified.
The selected digit is indicated by the flashing bright
digit.

D. Press the increment or decrement keys (indicated by

the up and down arrows) to modify the selected
digit for the desired memory location.

Method 2: Select Memory Location

A. Press the VOLTS/MEMORY key to select MEMORY

STEP. The present memory location is displayed on
the left display.

B. Press the SELECT key to select the left display. The

selected display is indicated by the flashing bright
digit.

C. Enter the desired memory location number using

the DATA keys.

D. Press ENTER.

3. Program the desired source. There are two methods for
programming the source. The source may be voltage or
current.

Method 1: Program the Source

A. Press either the VOLTS/MEMORY STEP key to dis-

play the source voltage on the left display, or the
AMPS/DWELL TIME key to display the source cur­rent on the right display.

B. Press the SELECT key to select the display to be

modified. The left display is for voltage and the right
display is for current. The selected display is indi­cated by the flashing bright digit.

C. Press the left or right key to select which digit is to

be modified. The selected digit is indicated by the
flashing bright digit.

D. Press the increment or decrement key to modify the

selected digit and source value. The output value is
updated continuously along with the display when
using the increment or decrement keys.

Method 2: Program the Source

A. Press the VOLTS/MEMORY STEP key to display the

source voltage, or the AMPS/DWELL TIME key to
display the source current.

B. Press the SELECT key to select the left display; the

left display for voltage or the right display for cur­rent. The selected display is indicated by the flashing
bright digit.

C. Enter the desired source value on the display using

the DATA key.

D. Press ENTER.

4. Program the desired dwell time. This may be done by
one of two methods.

Method 1: Program Dwell Time

A. Press the AMPS/DWELL TIME key if dwell time is

not displayed. The present dwell time is displayed
on the right display.

B. Press the SELECT key to select the left display. The

selected display is indicated by the flashing bright
digit.

C. Press the left or right key to select the digit to be

modified. The selected digit is indicated by the flash­ing bright digit.

D. Press the increment or decrement key (indicated by

the up and down arrows) to modify the selected
digit and dwell time. The value is updated continu­ously along with the display when using the incre­ment or decrement keys.

Method 2: Program Dwell Time

A. Press the AMPS/DWELL TIME key if not in the

dwell time mode. The present dwell time is dis­played on the right display.

B. Press the SELECT key to select the left display. The

selected digit is indicated by the flashing bright
digit.

C. Enter the desired dwell time using the DATA keys.

D. Press ENTER.

2-2

5. Select the desired memory control mode (single step, sin­gle cycle or continuous).

6. Connect appropriate load.

7. Select remote or local sensing (rear panel switch).

8. Program the instrument to the operate mode by pressing
the OPERATE/STANDBY key.

9. If applicable press the START/STOP key to start the
selected memory control mode.

Notes

1. Using the increment or decrement keys to either exceed
the maximum value for that range or change sign, briefly
displays an error message and the last key pressed is
ignored. Refer to Tables 3-4, 3-5, and 3-6 for front panel
messages.

2. Using the increment and decrement keys to adjust the
most significant digit does not change the range. The
range error message is displayed for about one second
and the instrument remains at the previous setting.

3. During the edit mode, if no activity has happened on the
front panel for approximately 20 seconds or if the
ENTER key is pressed, the edit mode is cancelled and the
display returns to normal intensity.

4. For the current function the output load must be, in gen­eral, non-inductive. A small amount of inductance in the
load can be tolerated if the inductive reactive voltage

di

L is limited to the maximum compliance voltage of the

-----­dt

range. Table 3-9 lists the maximum inductive reaction
voltage for each current range. Refer to paragraph 3.12.3.

5. Operation of the Model 228 as a power sink produces
heat. The Model 228 employs a fan for forced air cooling.
Do not block the airflow of the fan. The instrument may
overheat and go into the thermal shut down mode.

6. When using the DATA keypad to modify the displayed
data, the actual value is not entered until the ENTER but­ton is pressed.

7. In the operate mode (OPERATE LED on), the actual volt­age and current are monitored and displayed. For exam­ple, if 5V, 5A are programmed and the load is drawing

2.3A, then 5V, 2.3A is displayed.

8. All of the front panel keys (except PROGRAM,
CANCEL, OPERATE and LOCAL) autorepeat if held in.

9. In the immediate mode (which uses DECADE keys and
output is updated along with the display), the ENTER
key need not be pressed. After approximately 20 seconds
the Model 228 cancels the edit mode and returns to the
previous operating mode. The new data remains.

10. The STANDBY LED is of amber color to distinguish it
from the OPERATE LED which is red.

11. If the internal operating temperature reaches over 100˚C,
the Model 228 displays an error message as shown in
Tables 3-4, 3-5, and 3-6. At this point the instrument locks
up and displays the error message. The Model 228 must

be turned off and allowed to cool down before continu­ing operation.

12. The Model 228 when first turned on, goes through a
power up sequence that is described in Section 3.

13. The Model 228 has a bipolar output. This means that the
polarity of the output may be reversed without having to
reverse the output leads.

14. All of the information programmed into the memory
locations is battery backed up. This means that if the
instrument is powered down, the information pro­grammed in the memory locations is not lost. The infor­mation remains in the memory location until changed by
the user.

15. Tables 3-4, 3-5, and 3-6 contain a complete list of front
panel messages and their definition. Included are error
and instrument status messages.

16. The user selects the range with the absolute location of
the decimal point. 1.000V selects the 1V range, 1V out­put. 1.00V selects the l0V range, 1V output. 001.V selects
the l00V range, 1V output.

17. Increment and decrement keys do not change the range
or polarity. These functions increase/decrease the mag­nitude of both positive and negative limits.

18. After power on, the current range select relays remain
open until the operate key is pressed the first time. This
effectively open-circuits the output and may cause tran­sients on the output during auto cal and the first time
operate is selected.

CAUTION
The MONITOR and MODULATION termi­nals remain connected to the Model 228’s
internal circuitry; therefore, large voltages
or currents may exist between OUT+ and
these terminals during calibration.

19. While in the standby mode, the output remains pro­grammed the same as when first programmed to
standby. Therefore range changes, source/sink status,
(etc.) take affect when operate is selected.

20. The front panel compliance graph may show multiple
LEDs. As an example; when current is zero, +0 and —0
are approximately the same magnitude so two LEDs will
show.

21. If the measured output current exceeds 200% of range,
the output is disconnected and the Model 228 is placed
in the standby mode. Normal operation returns by press­ing the OPERATE key.

2.3 GENERAL OPERATION NOTES

1. Using the increment or decrement keys to either exceed
the maximum value for that range or change sign, causes
the Model 228 to briefly display an error message. The last
key pressed is ignored. Refer to Tables 3-4, 3-5, and 3-6 for
front panel messages.

2-3

2. Using the increment or decrement key to adjust the most
significant digit does not change the range. The range
error message is displayed for about one second; and the
instrument remains at the maximum display for that
range or zero, whichever is programmed.

3. During the edit mode, if no activity has happened on the
front panel for approximately 20 seconds, or if the
ENTER key is pressed, the edit mode is cancelled. The
display returns to normal intensity.

4. For the current function, the output load must be, in gen­eral non-inductive. A small amount of inductance in the
load can be tolerated if the inductive reactive voltage

di

L , is limited to the maximum compliance voltage of

-----­dt

the range. Table 3-4 lists the maximum inductive reaction
voltage for each current range.

5. Operation of the Model 228 as a power sink produces
heat. The Model 228 employs a fan for forced air cooling.
Do not block the airflow of the fan. The instrument may
overheat and go into the thermal lock up mode.

6. When using the DATA keypad to modify the displayed
data, the actual value is not entered until the ENTER but­ton is pressed.

7. In the operate mode (OPERATE LED on), the actual volt­age and current are monitored and can be displayed. For
example, if 5V, 5A are programmed and the load is draw­ing 2.3A, then 5V, 2.3A is displayed.

8. All of the front panel keys (except PROGRAM,
CANCEL, OPERATE, and LOCAL) autorepeat if held in.

9. In the immediate mode (using DECADE keys and the
output is updated along with the display) the ENTER
key need not be pressed. After approximately 20 sec­onds, the Model 228 cancels the edit mode and returns to
the previous operating mode. The new data remains.

10. The STANDBY LED is of amber color to distinguish it
from the OPERATE LED which is red.

11. If the internal operating temperature reaches over l00˚C,
the Model 228 displays an error message as shown in
Table 3-4. At this point, the instrument locks up with the
error message displayed. The Model 228 must be turned
off and allowed to cool down before continuing
operation.

12. The Model 228 goes through an autocalibration cycle
when the instrument is powered on. Refer to the mainte­nance section for complete details.

13. The Model 228 has a bipolar output. This means that the
polarity of the output may be reversed without having to
reverse the output leads.

14. All of the information programmed into the memory
locations is battery backed up. This means that if the
instrument is powered down, the information pro­grammed in the memory locations is not lost. The infor­mation remains in the memory locations until changed
by the user.

15. Tables 3-5, 3-6, and 3-7, contain a complete list of front
panel messages and their definition. The messages
include: error messages and instrument status messages.

2.4 STANDBY MODE NOTES

The following situations depict when the Model 228 output is
electrically disconnected (via internal relays) from the
instrument.

1. Power is off.

2. During the auto calibration cycle. Upon power up, until
the end of the calibration cycle and during a portion of
front panel Program 6.

3. Within a few line cycles for low or missing line voltage. If
the microprocessor is reset, the normal power up
sequence occurs. If the microprocessor is not reset, the
next time the A/D is triggered (approximately six times
a second) or when the output is changed.

In the standby mode the Model 228 output is still active. The
standby mode has the same effect as programming the out­put for the following conditions:

1. 0V +four counts (on the same voltage range and same
polarity).

2. 0A +four counts (on the same current range and same
polarity).

3. MOD V off.

4. MOD I off.

The output is NOT disconnected. Programming the output
for the new values, ranges polarity, sink mode or modulation
does NOT change the output until the Model 228 is placed in
the operate mode.

Notes

1. Since the output is still active, the quick disconnect card
should be removed from the mainframe BEFORE any
wiring changes are to be made.

2. The Model 228 looks like a short or an open circuit to an
external source. This depends on whether the voltage
polarities oppose or match before the Model 228 is
placed in standby. Polarity changes do not affect the out­put until the Model 228 is placed in the operate mode.

3. Large reactive loads are not immediately discharged by
placing the Model 228 in the standby mode. This is
because the 0V setting does not change the current
through an inductor and the 0A setting does not change
the voltage across a capacitor. In reality, capacitors and
inductors discharge at approximately 0.4% of range
when the Model 228 is in the standby mode.

2-4

SECTION 3

FRONT PANEL OPERATION

3.1 INTRODUCTION

Information in this section concerns front panel operation of
the Model 228 and is divided into four categories: operating
instructions, operating examples, front panel programs, and
applications. Operating instructions include using the
Model 228 to source or sink, voltage or current, in the posi­tive or negative direction. Operating examples cover many
aspects of Model 228 operation. The front panel programs
section describes each program and gives a few examples of
Model 228 uses.

3.2 PREPARATION FOR USE

The following steps must be performed to prepare the
Model 228 for operation. These steps can be performed
quickly and will ensure proper line voltage and fuse
selection.

3.2.1 Line Voltage Selection

The Model 228 may be operated from either 105V-125V or
210V-250V, 50Hz or 60Hz power source. The instrument was
shipped from the factory set for an operating voltage that is
marked on the rear panel. The operating voltage of the
instrument is internally selectable. Refer to Section 7 Mainte­nance, for information on setting the line voltage.

CAUTION
Do not attempt to operate the instrument
on a supply voltage outside the indicated
range. Damage to the instrument may
occur.

3.2.2 Fuse Checks

It is important to check each of the three fuses for proper rat­ing before applying power to the Model 228. If the voltage
was recently changed, the linear supply fuse (LINE FUSE 1)
and the switching supply fuse (LINE FUSE 2) must also be
changed to accommodate the new line voltage. The output
fuse (OUTPUT FUSE) should also be checked for proper rat­ing. Refer to Section 7 Maintenance, for information on
proper fuse rating.

3.3 POWER UP

NOTE

To ensure compliance with EMI requirements,
the Model 228A should be connected to AC
power with the specified filtered power cord
provided with the unit.

Plug the Model 228 into the proper power source. (see Table
3-1.) For fuse replacement of line switch (S102) setting, refer
to Section 7 Maintenance.

WARNING
Ground the instrument through a properly
earth grounded receptacle before operat­ing. Failure to ground the instrument may
result in severe injury or death in the event
of a short circuit or malfunction.

Table 3-1. Line Voltage Setting

Switch

Setting

Input V oltage

090V - 110V*

105V - 125V*
180V - 220V*
210V - 250V*

* Operation at these input voltages requires power supply

modifications. Refer to the maintenance section of this manual for
more information.

Turn the instrument on. The Model 228 runs through a power
up sequence that is described as follows:

1. Immediately after turning on the Model 228 via the front
panel POWER switch, both displays indicate the
following for several seconds:

(SW302) Fuse 1 Fuse 2

115V
115V
230V
230V

6.3A, 250V
5A, 250V

3.15A, 250V

2.5A, 250V

1A, 250V
3/4A, 250V

0.5A, 250V
3/8A, 250V

+ +

CAUTION
Check all three fuses for appropriate
rating. The fuse ratings are listed in Tables
7-1 and 7-2, and they are also shown on
the rear panel. Incorrect rating may cause
damage to the instrument in case of short
circuit or malfunction.

A. This is a display test. The operator can note inopera-

tive display segments by comparing the Model 228’s
display with the above figure.

B. In addition, all LEDs are turned on for the same

period of time. The LEDs include: VOLTS, MEM STEP,
AMPS, SECONDS, STANDBY, OPERATE, STOP,

3-1

START, SINGLE MODULATE I, MODULATE V and
SINK ONLY. All of these LEDs light simultaneously if
operating properly.

C. While the display test is running, the Model 228 is per-

forming a digital self test on the RAM circuitry and
cyclic redundancy check (CRC) on the ROM circuitry.
If there is a problem, the Model 228 displays an error
message. For further information, refer to Section 7
Maintenance.

If the Model 228 did not pass the RAM test the following is
displayed.

If the Model 228 did not pass the ROM test the following is
displayed.

2. The Model 228 displays the software revision level. The
following is an example of software revision Al.

3.5 ENVIRONMENTAL CONDITIONS

Operate the Model 228 in an environment with an ambient
temperature within the range of 0°C to SO”C, up to 35°C at
80% non-condensing relative humidity. Environmental con­ditions for storage are from -25°C to 70°C.

3.6 OPERATING INSTRUCTIONS

The following instructions show how to operate the Model

228 using the front panel controls. In order to operate the

Model 228, the user must understand the front and rear panel

controls. It is important to read and follow the safety precau-

tions and warnings before operating the instrument. A brief
description of the front panel controls is provided in Table

3-2. A more detailed description of the front panel controls is
contained in paragraph 3.7. A brief description of the rear
panel terminals and controls is provided in Table 3-3. A more

detailed description of the rear panel controls is contained in
paragraph 3.8. Figure 3-2 shows the front panel of the Model

228. Figure 3-3 shows the rear panel of the Model 228. A
graph of operation is contained in Figure 1.

3. Next, the Model 228 displays the present primary address.
The following is an example of primary address set to 11.

3.4 WARM UP

In order to achieve rated accuracy, the Model 228 requires ten
minutes for warm up.

NOTE

To achieve rated accuracy, run Program 6 immedi­ately after the lOminute warm-up period.

-I

= +115V (DESTRUCTWE LIMIT1
= -CURRENT LIMIT I + PROGRAMMED)
= +VOLTAGE LlMlT (+PROGRAMMEDl I = -VOLTAGE LIMIT t - PROGRAMMEDI

= + CURRENT LIMIT (+ PROGRAMMED1 J = -CURRENT LIMIT (-PROGRAMMED)
E = -VOLTAGE LIMIT I + PROGRAMMED)
F = ZOA FUSE

G = - 115 IDESTRUCTlVE LIMIT)
H = + CURRENT LIMIT I -PROGRAMMED)

K = + VOLTAGE LIMIT I -PROGRAMMED)
L = 20A FUSE

Figure 3-l.Graph of Operation

3-2

Table 3-2. Front Panel Controls

Control
POWER ON/OFF
OPERATE/STANDBY

VOLTS/MEMORY STEP
AMPS/DWELL TIME

DISPLAY MODIFY GROUP
SELECT

DECADE

ENTER
DATA

MEMORY CONTROL GROUP

Descriotion

Turns the unit on or off.

Places the output in either standby or operate. Standby programs the output

terminals for OV, OA. Operate places the programmed value (voltage or cur-

rent) on the output terminals.
Places the left display (viewed from the front panel) in either the volts display

mode or the memory step mode.
Places the left display (viewed from the front panel) in either the amps display

mode or the dwell time display mode.

Determines which display (left or right) to modify.

The DECADE keys (left, right, up and down) modify the selected display. The

left and right keys (indicated by the left and right arrows) select which digit is
to be modified. The increment and decrement keys (indicated by the up and
down arrows) increment or decrement the value of the selected (bright) digit
and therefore the displayed value by one unit each time the key is pressed.
The output tracks the increment or decrement of the displayed value.

The ENTER key places the displayed data into the present memory location.
The DATA keys enter the desired value on the display. ENTER must be

pressed to update the value to the output. The DATA keys also activate the
desired front panel program. Refer to paragraph 3.11 for front panel pro­grams.

START/STOP
SINGLE STEP

SINGLE CYCLE

CONTINUOUS

PROGRAM CONTROL GROUF
PROGRAM

CANCEL

LOCAL

The START/STOP key enables or disables the memory control functions.

Selects the SINGLE STEP memory control function which allows the user to
step through the programmed memory locations one at a time. Each suc­cessive key pressed advances the unit to the next memory location. The

memory control mode must be activated in order for single step to operate.
Selects the single cycle memory control function which allows the user to run

through one complete cycle of the programmed memory location. The

memory control mode must be activated in order for Single Cycle to operate.
Selects the CONTINUOUS memory function which allows the user to run

through the programmed memory locations continuously. The memory con­trol mode must be activated in order for CONTINUOUS to operate.

The PROGRAM key is used as the first step in activating the front panel pro­grams.

The CANCEL key has two functions. In the program mode, the CANCEL key
takes the instrument out of the program mode. During entry of new data, the

CANCEL key terminates editing. The instrument is then returned to the

previous operating mode.
The LOCAL key enables front panel operation. In the remote mode (over

IEEE-488 bus), pressing the LOCAL key enables front panel operation and
takes the Model 228 out of the remote mode.

3-3

Table 3-3. Rear Panel Description

Connections/Controls

OUTPUT CONNECTOR

SENSE

CURRENT MONITOR
TRIGGER IN
TRIGGER OUT

EXTERNAL MODULATION
FUSE 1

FUSE 2
FUSE 3

IEEE-488 Connector
LINE RECEPTACLE

Description

The output connections are located on a card that is inserted into the

Model 228 mainframe. When the connector is removed from the mainframe

the output connections are disengaged from the actual output potentials.
The sense connectors are located on a card that is inserted into the Model

228 mainframe. The sense lines are used to sense the output at the output
connector (Local) or sense the output at the load (Remote).

This connection supplies a voltage proportional to the output current for
use with oscilloscopes or DMMs.

The TRIGGER IN connector accepts a TTL level negative going pulse of
greater than 10pec to initiate the selected memory mode.

The TRIGGER OUT connector outputs a lTL level negative going pulse of
greater than lO/rsec at the end of each programmed dwell time.

This connector allows the output (voltage or current) to be externally
modulated.

This is the line power fuse for the linear power supply on the analog board.
The fuse is rated as shown in Tables 7-1 and 7-2. If this fuse is blown the

Model 228 will not power up.

This is the switching supply fuse. It is rated as shown in Tables 7-1 and
7-2. If this fuse is blown there is no output present.

This is the output fuse. The fuse is rated at 20A.
This connector is used to connect the instrument to the IEEE-488 bus. The

IEEE interface functions are marked above the connector.

The line receptacle connects to a three wire line cord which provides con­nections to the line voltage.

3-4

3.7 FRONT PANEL DESCRIPTION

OPERATION GROUP

POWER ON/OFF-The ON/OFF switch operates on the
push-push principle. Depressing this switch turns the instru­ment on. Once the instrument is on, pressing (releasing) this
switch turns the instrument off. When the Model 228 is turn-

ed on, the output is programmed to about OV, OA and the

programmed settings are displayed. Note that the Model 228
does not change range polarity or sink status while in the
standby modes, and external modulation is disabled.

VOLTS/MEMORY STEP-The VOLTS/MEMORY STEP
key is an alternate action control which places the left display
in either the volts display mode or the memory step mode. In
the volts display mode, the voltage for the present memory
location (step) is displayed on the left display. In the memory
step mode, the present memory location is displayed on the
left display. This key allows the user to view either the pre­sent memory location or the voltage at the present memory
location. There are 100 memory locations (steps). Each
memory location contains five parameters (Voltage, Current,

Dwell Time, Modulation on or off and Sink Mode on or off).
These parameters are defined (programmed) by the user. This
means that each memory location may have its own unique
values.

OPERATE/STANDBY-The OPERATE/STANDBY key is
an alternate action control (toggle) which places the Model
228 in either the operate mode or the standby mode. In the
operate mode, the OPERATE LED is turned on and the pro­grammed source value is present on the output terminals. In
the standby mode, the STANDBY LED is turned on the out­put is programmed to approximately zero and the displayed
value remains the same.

In the standby mode the Model 228 is still active. The standby
mode has the same effect as programming the output for the
following conditions:

1. OV + four counts (on the same voltage range and polarity).

2. OA +four counts (on the same current range and same
polarity).

3. MOD V off.

4.. MOD I off.

The output is NOT disconnected. Programming the output
for a new value, range polarity, sink mode or modulation,

does not change the output until the Model 228 is placed in
the operate mode.

AMPS/DWELL TIME-The AMPS/DWELL TIME key is an
alternate action control which places the right display in
either the amps display mode or the dwell time display mode.
In the amps display mode, the current for the present memory
location is displayed on the right display. In the dwell time
display mode, the dwell time for the present memory location
is displayed on the right display. This key allows the user to
view either the dwell time for the present memory location or
the current for the present memory location. The dwell time
ranges from 1Omsec to 1000sec.

DISPLAY MODIFY GROUP (EDIT)

DISPLAY MODIFY

0

SELECT

0

A

ENTER

0

IO

DECADE

01)

Notes

1. Since the output is still active the quick disconnect board
should be removed from the mainframe before any wiring
changes are to be made.

2. The Model 228 looks like a short or an open circuit to an
external source. This depends on whether the voltage
polarities oppose or match before the Model 228 is placed
in standby. Polarity changes do not affect the output until

the Model 228 is placed in the operate mode.

3. Large reactive loads are not discharged immediately after
placing the Model 228 in the standby mode. This is because
the OV setting does not change the current through an in­ductor and the OA setting does not change the voltage
across a capacitor. In general, capacitors and inductors
discharge at approximately 0.4% of range when the Model
228 is in the standby mode.

0

‘I

SELECT-The SELECT key determines which display (left or
right) can be configured. Pressing the SELECT key once
selects the previously selected display for modification.
Subsequent key presses toggle the edit mode between
displays. Use the SELECT key before modifying the volts,

memory step, amps or dwell time functions.

DECADE-The DECADE keys (right, left, up and down)
modify the selected display. The left and right keys (indicated

3-7

by left and right arrows) select which digit on the display is to
be modified. These keys wrap the cursor around to the op­posite end (most significant) digit if attempting to go beyond
the left most or right most (least significant) digit. The modify
digit is indicated by the “bright flashing“ digit on the display.
The left and right keys autorepeat if held in. That is, the left
key when pressed and held in keeps advancing to the next
digit to the left. The same is true for the right key except, of
course, it advances to the right.

The increment and decrement keys (indicated by the up and
down arrows) increment and decrement the modify (bright)
digit and therefore the displayed value. The modify digit is

modified by one unit each time the increment or decrement

Table 3-4. Front Panel Messages

key is pressed.
autorepeating. That is, pressing and holding in the increment
key increments the display continually until the range limit is
reached or the key is released. The same is true for the decre­ment key.

The increment key has the mathematical carry capability.
This means that if the modify digit is a 9, pressing the incre­ment key once sets the modify digit to 0 and the next signifi-

cant digit is increased by one. If the display is at the miuc­imum (lOlO), pressing the increment key causes an error
message to be displayed for approximately one second. Refer

to Tables 343-5 and 3-6 for front panel messages and Table
3-7 for the power up default conditions. The display then
returns to the previous condition,

The increment/decrement keys are

Message

Message

Left Display Right Display Comments

buF

+5

-5

+15

-15

+115

-115

- 500
+ 900

+ loo0

CAL
CAL
CAL
CAL

no

Ad

no

IEEE

buF

no

Err
Err + 5V analog supply is outside of a f 50% range.
Err
Err + 15V analog supply is outside of a &50% range.
Err
Err + 115V analog supply is outside of a f 50% range.
Err - 115V analog supply is outside of a f 50% range.
Err
Err

Err
Err1
Err2
Err3
Err4

AdFb

Err

Pro

Err

End

IddC

IddCo

rn

Bad data was copied from the memory buffers.

-5V analog supply is outside of a f50% range.

- 15V analog supply is outside of a *50% range.

Temperature sensor is not operating properly.
Heat sink temperature has increased past 90°C. Turn sink mode on.

Temperature exceeds 1OOOC. The Model 228 turns off the switching supply
and locks up the front panel. Turn off power and let it cool down.

Calibration error. Autocalibration cannot be performed. Voltage DAC (Digital
to Analog Converter) gain is out of cal range.

Calibration error. Auto calibration cannot be performed. Voltage DAC (Digital
to Analog Converter) offset is out of cal range.

Calibration error. Auto calibration cannot be performed. Current DAC (Digital
to Analog Converters) gain is out of cal range.

Calibration error. Auto calibration cannot be performed. Current DAC (Digital
to Analog Converter) offset is out of cal range.

No data transmits across the opto-isolators.
A/D error. The A/D does not read the IV reference and ground properly.
No program exists. Illegal program number attempted.
IEEE address error. An attempt to enter an illegal IEEE address was made.

The range of IEEE addresses is O-31.

Buffer end. The end of memory locations is reached. Maximum of 100 loca-

tions.

Illegal Device-Dependent Command
Illegal Device-Dependent Command Option
No remote. The instrument was not in remote when programmed.

3-8

Table

3-5. Front Panel Messages and Prompts

Message

Left Display

IEEE

rEU

Pro

CAL

U
U

I

I
Sln
Sln

COP

Message

Right Display

11

A

?

20

on

Off

on

Off

on

OFF

002

Comments
IEEE address. Address 11 shown. Front panel Program 3 activated or power

up sequence.
Software revision level. Revision A shown.
Prompt to enter the number of the desired front panel program.
Calibration. The Model 228 is going through the autocalibration sequence.

The Model 228 counts down from 20 to 0 during this sequence. This se­quence may be bypassed by pressing the CANCEL key. However, the
previous cal will be valid.

External modulate V program is on.
External modulate V program is off.
External modulate I program is on.
External modulate I program is off.
Sink program on.
Sink program off.
Copy program enabled. Contents of memory location 1 duplicated into

memory location 2.

Table

3-6. Error Messages (Either Display)*

Message Comments

oFL Overflow. Attempt to output beyond the present range. Reading

exceeds 1999 on any range.

rnG Range. Attempt to program beyond the present range. Illegal

range combination.

Err

Error. Exceeded 1010 limit or attempt to program below zero.

*NOTE: These messages appear on the display where the error occurred.

3-9

Table 3-7. Power Up Default Conditions

Mode
Display

Function
Data Format
EOI
SRQ
Program Mode
Range
Trigger
Terminator
Buffer Location
Voltage
Current
Dwell Time
Sink Mode
External Modulation A

Program 1
Program 2
Program 3
Program 4
Program 5
Porgram 6

Program 9

Value Status

DO Left Display= Volts, Right Display= Amps. Left Display ready for edit.

FO Standby (output programmed to +4 counts on present range)
GO Prefix of buffer location contents.
KO Send EOI.

MO Disabled

PO Single Step Mode.
RO Autorange
T6 Stop on X

CR LF Carriage Return Line Feed

BOO1 Location #I

V Dependent on previously programmed values of memory location 1.

W Dependent on previously programmed values of memory location 1.

S

C Dependent on previously programmed values of memory location 1.

Copy Disabled

Sink Dependent on previously programmed values of memory location 1.
IEEE Not affected

Mod V Dependent on previously programmed values of memory location 1.

Mod I Dependent on previously programmed values of memory location 1.

Test Jl if passed; in status byte

Reset Disabled

I Dependent on previously programmed values of memory location 1.

Dependent on previously programmed values of memory location 1.
Dependent on previously programmed values of memory location 1.

J2 if failed; in status byte

The decrement key has the mathematical borrow capability.
This means that if the modify digit is 0, pressing the decre­ment key sets the modify digit to 9 and the next significant
digit is decreased by one unit. If the display is 0000, pressing

the decrement key causes an error message to be displayed for
approximately one second. The display then returns to the
previous condition.

Using the increment and decrement keys to change the sign of

the displayed value causes and error message to be displayed
for approximately one second. The display then returns to the
previous condition.

The DECADE keys operate in the immediate mode. In the im-

mediate mode, the output value is updated as the display is

3-10

updated. For example: If 95.OV is displayed and present on
the output, selecting the 5 digit and pressing the increment
key increases the display to 96.OV. At the same time, the out­put is also changed to 96.OV.

ENTER-The ENTER key loads the displayed data into the
present memory location. Pressing the ENTER key after
modifying the displayed data, loads the new data into the
present memory location. The display then reverts to normal
intensity and the display modifying operation (edit) is ter­minated. The DATA keys do not affect the output until the
ENTER key is pressed.

DATA GROUP

7

0

DATA

0

START/STOP-The START/STOP key serves three func­tions that are described as follows:

1. When the START/STOP key is pressed, the selected
memory control mode (Single Step, Single Cycle or Con­tinuous) is started.

2. Pressing the START/STOP key while the memory control

8

9

0

mode is running stops the memory control mode at the
present memory location.

3. In the single step memory control mode, pressing the
START/STOP key advances the instrument to the next
programmed memory location.

4

0

MOD V MOD I

c&l c&l el

COPY SINK

0

0

5

0

l

0

6

0

TEST

IEEE

+/-

0

,

DATA-The DATA keys have dual functions. In the enter

mode, these keys enter the desired number on the display. In

the program mode, the keys activate the desired program.
The front panel programs are described in paragraph 3.11.
Entering data on the display using the DATA keys always
start with the left most (most significant) digit on the display.

MEMORY CONTROL GROUP

MEMORY CONTROL

The START/STOP LED is turned on while the single cycle
and continuous memory control mode is going through its cy-

cle. In the single step memory control mode, the START/
STOP LED is turned off for the duration of the programmed
dwell time of the memory location.

When the Model 228 is in the standby mode (OPERATE LED
is turned off) and either the single cycle or continuous
memory control mode, the START/STOP key continues to
control the buffer with no output present on output ter­minals. For example: The continuous mode keeps going on its
cycle even though the Model 228 is in the standby mode
(STANDBY LED on).

SINGLE STEP-In the single step mode (SINGLE STEP LED
is on), the memory location is advanced by one step each time

the START/STOP key is pressed or the proper external trig­ger pulse is received. The voltage , current and dwell time
may be different for each memory location. That is, the user

defines these parameters for each memory location.

At the completion of the programmed dwell time a pulse is
sent out via the external trigger output connector. The

START/STOP LED is turned off at this time. The pulse is a
negative going TTL level pulse with a duration of greater than

10psec. The pulse could be used to trigger another instrument
into its special function (e.g. chart recorder, DMM, etc).

STOP

0 f-J START

j--J SINGLE STEP

[ q

SINGLE CYCLI

0 CONTINUOUS

Pressing the SINGLE STEP key when in the last programmed
memory location and the single step mode causes the Model
228 to revert to memory location 1.

A zero dwell time for any memory location causes the Model
228 to jump to memory location 1.

3-11

SINGLE CYCLE-In the single cycle mode (SINGLE CYCLE

LED is on), and upon actuation of the

upon receiving a proper external trigger pulse, the Model 228
advances to the next memory location. After the duration of
the dwell time for the memory location the Model 228 ad­vances to the next memory location. START/STOP LED is
turned on. This cycle continues advancing through the pro­grammed memory location until the last programmed loca-

tion is reached or stops at last memory location before zero
dwell time. Pressing the START/STOP key jumps the Model
228 to memory location 1.

START/STOP key or

ADDITIONAL TEST SEQUENCES
As previously discussed, a test sequence cycle is terminated

by the first memory location that has a dwell time of 0
seconds. In the single step mode, the test

sequence can be

stopped at the last programmed memory location of the
sequence. In the single cycle mode, the cycle always stops
at the last programmed memory step

location. Stopping

the test sequence at the last programmed memory steps
makes it possible to use other programmed test sequences.

The voltage, current and dwell time parameters may be dif­ferent for each memory location. That is, the user defines

these three parameters.

At the completion of each programmed dwell time, the Model
228 outputs a negative going TTL level pulse of greater than
1Opsec in duration. The pulse appears at the external trigger
output connector on the rear panel. This pulse could be used
to trigger another instrument into operation (e.g. DMM, con-

troller, etc.)

CONTINUOUS-In the continuous mode (CONTINUOUS
LED is on) and upon actuation of the START/STOP key or

after the proper external trigger pulse is received, the Model
228 advances to the next programmed memory location.
After the duration of the present memorylocation the Model

228 advances to the next programmed memory location and

remains there for its programmed dwell time. This cycle con-

tinues until the last programmed memory location is reached

or a memory location with a zero dwell time is reached. At

this point the Model 228 jumps to memory location 1. The cy-

cle then repeats and continues repeating until it is stopped.

The voltage, current and dwell time parameters may be dif-

ferent for each memory location. That is, the user defines

these

three parameters. Just like the single step and single cy-

cle modes, in the continuous mode a negative going TTL level

pulse

of greater than 1Opsec appears at the external trigger

output

connector upon completion of each programmed
dwell time. This pulse could be used to trigger another instru­ment into its function in the system (e.g. start measurement

cycle on DMM, inform a controller that the dwell time is end-

ed, etc.).

the Model 228 to memory location 1.

A zero dwell time for any memory location reverts

The instrument must be in the single step or single cycle
mode to use more than one test sequence. At the end of
the first test sequence, (last memory step location of the
sequence displayed), advance the display (using the
DISPLAY MODIFY keys) to the memory step location im­mediately before the first programmed memory location of

the next test sequence. This second test sequence wiIl then
start when the START button is pressed.

Example-The following example

will illustrate how to use

two test sequences:

1. Program memory locations 1 through 9 so that they have
some dwell time. This represents the first test sequence.

2. Program memory location 10 for a dwell time of 0

seconds. This step will terminate the first test sequence.

3. Program memo
also have some

test

sequence.

4. Place the instrument in the single cycle mode.

locations 11 through 19 so that they

well time. This represents the second

3

5. Press the START button. The instrument wiIl cycle once
through the first test sequence and stop at the last

memory location of that sequence.

6. Using the DISPLAY MODIFY buttons, advance the
display to memory location 10.

7. Press the START button. The instrument will cycle once
through the second test sequence.

Note: If the single step mode is used on the above ex­ample, stop the cycle of the first test sequence at memory
step location 9.

In the continuous mode, the instrument continually cycles
from the first programmed memory step to the last pro­grammed memory step. Since the instrument wiIl not stop
at the last programmed memory location, only one test se­quence can be used in the continuous mode.

3-12

PROGRAM GROUP

PROGRAM CONTROL

n PROGRAM

As another example consider that the LED just to the right of

the -V( -VCJNK) symbol is turned on. As in the previous
example, four parameters are known by noting the COM­PLIANCE graph.

1. The polarity of the voltage is negative

2. The polarity of the current is positive.

3. Voltage is the controlling function.

4. The instrument is operating as an active load (current

sink).

0

CANCEL

PROGRAM-The PROGRAM key is used as the first step in
activating the front panel address.

CANCEL-The CANCEL key has two levels of operation
and they are described as follows:

1. Pressing the CANCEL key when a front panel program is
running terminates the program mode and reverts the
Model 228 to the previous mode of operation.

2. Pressing the CANCEL key during the entry of data in any
of the programs, reverts the new data to the previous data,
terminates the program and then terminates the program
mode. The instrument is then reverted to the previous
mode of operation.

COMPLIANCE Graph-The COMPLIANCE graph indicates
the state of the output. Refer to the front panel and/or
following Figure. By noting the front panel COMPLIANCE
graph four parameters concerning the output are known.

1. The polarity of the voltage.

2. The polarity of the current.

3. The controlling function (Voltage or Current).

4. Operation as a sink or source.

-I

STATUS GROUP

m LOCAL 0 REMOTE

+I

.

STATUS

For example: If the LED just above the +I ( +I~c)~R& sym­bol is turned on, then four parameters are known.

1. The polarity of the voltage is positive.

2. The polarity of the current is positive.

3. The controlling function is current.

4. The instrument is operating as a source.

The reason that the current is the controlling function is that
the line for that LED goes through the +I axis the current is
constant and the voltage is the parameter that varies. For line
intersecting the voltage axis it is the voltage that is the con­trolling function and the current is the parameter that varies.

q

0 TALK
0 MODULATE I

0 MODULATE V
0 SINK ONLY

LISTEN

LOCAL-In the remote mode (IEEE-488 bus operation) of
operation all front panel controls except LOCAL and
POWER ON/OFF are disabled. Pressing the LOCAL key
takes the Model 228 out of the remote mode and enables all of
the front panel controls.

3-13

REMOTE LED-When the REMOTE LED is on, the Model
228 is in the remote mode of operation (IEEE-488 bus opera­tion). When the REMOTE LED is off, the Model 228 is in the
local mode of operation. Refer to Section 4 for more informa­tion concerning IEEE-488 bus operation.

VOLTS/MEMORY STEP Display-The left display (viewed
from the front panel) is used exclusively for the volts and the

memory step modes. The display is a 3% digit + 1999 count
LED display. The VOLTS LED and the MEMORY STEP LED
are located next to the display. These LEDs indicate which
mode is activated (volts or memory step).

TALK LED-When the TALK LED is on, the Model 228 is in
the talk mode. Refer to Section 4 for more information con­cerning IEEE-bus operation.

LISTEN LED-When the LISTEN LED is on, the Model 228 is

in the listen mode, Refer to Section 4 for more information

concerning IEEE-488 bus operation.

MODULATE I-When the MODULATE I LED is on, exter-

nal current modulation is enabled. An external

be superimposed on the ouput current through the external

modulation connector on the rear panel. This assumes that

current is the controlling function. Current ,is the controlling

function when the Model 228 voltage (V) setting is greater
than the product of the Model 228 current (I) setting and the
user load.

MODULATE V-When the MODULATE V LED is on, the
Model 228 is in the voltage modulation mode, An external
AC signal up to the specified limits may be superimposed on
the output voltage through the quick disconnect board on the

rear panel. This assumes that voltage is the controlling func­tion. Voltage is the controlling function when the Model 228
voltage (V) setting is less than the product of the Model 228
current (I) setting and the user load.

SINK ONLY-When the SINK ONLY LED is on, the Model
228 is in the sink mode of operation. Take note of the front
panel COMPLIANCE graph. The COMPLIANCE graph in­dicates which quadrant of sink mode the Model 228 is
operating.

AC

signal can

DISPLAYS

AMPS/DWELL TIME Display-The right display (viewed

from the front panel) is used exclusively for the amps and the
dwell time modes. The display is a 3% digit 3~1999 count
LED display. The AMPS LED and the DWELL TIME LED are
located next to the display. These LEDs indicate which mode

is activated (amps or dwell time).

3.8 REAR PANEL DESCRIPTION

OUTPUT CONNECTOR GROUP

Output Connector-The output connector (OUT+ and
OUT - terminals) are located on the quick disconnect board.
This board fits into the Model 228 mainframe. The output is
disconnected when the quick disconnect board is removed
from the mainframe. The output terminals are screw type ter­minals that accept up to #16 AWG wire. Only insulated lugs
should be used to connect to the output terminals on the
quick disconnect board. An example of an insulated lug is
Keithley part number LU-99-2.

CAUTION
Care should be taken to avoid shorting the
terminals on the quick disconnect board.
Instrument damage may occur.

Terminals-The sense terminals are located on the

Sense
quick disconnect board. The sense terminals are used in the
volts mode. When a load is connected to the Model 228, there
is an IR lead drop between the load and the Model 228. In

some situations the IR lead drop is negligible and not need be

taken into consideration. This is where local sensing may be

used. In other situations the IR lead drop may cause an error

in the actual voltage delivered. In this case the Model 228
could be configured for remote sensing.

LEFT DISPLAY

3-14

RIGHT DISPLAY

Remote sensing compensates for the IR lead drop by main­taining regulation at the load instead of at the output ter­minals of the Model 228.

When using remote sensing, the output sense + (S + ) terminal

must be connected to OUT+ and the output sense -(S-)
terminal must be connected to OUT- at the load.

CAUTION
Take care to connect the sense terminals to
the load with the proper polarity. Improper
polarity may result in damge to the instru­ment and the load.

Current Monitor Terminals-The Model 228 monitors the
output current internally and provides a voltage proportional
to the output current for the user.

TRIGGER GROUP

TRIGGER

@ @

TRIGGER ON

NEGATIVE

lTL HIGH

CAUTION: DO NOT EXCEED STANDARD TTL LEVELS

GOING

PULSE

TRIGGER IN-The TRIGGER IN connector is a female BNC
connector that accepts a TTL level negative going pulse of
greater than 10psec that when received starts the selected
memory control mode (Single Step, Single Cycle or Con­tinuous). In the single step mode, one pulse is required for
each memory location. In the single cycle mode, one pulse re­quired for each cycle of the programmed memory locations.
In the continuous mode, one pulse is required to start the cy­cle.

TRIGGER OUT-The TRIGGER OUT connector is a female
BNC connector that outputs a TTL level negative going pulse

of greater than 1Opsec at the end of the programmed dwell
time. This pulse appears at the end of the dwell time for each

programmed memory location.

External Modulation Terminals-The external modulation
terminals consists of two screw terminals that are located on
the quick disconnect board. External modulation allows the
user to modulate the output voltage or current. With an AC
signal (up to specified limits). The limits are given in the in­strument specifications that precede Section 1 and Figure
3-6. Modulation input is a voltage across a 6.8k impedance.
The front panel MODULATE I and MODULATE V LEDs in­dicate whether the output current or output voltage is being
modulated.

When using the external modulation, use shielded cables.
Connect the shield to output LO. This action shields any ex­traneous noise from being introduced into the signal.

3-15

AC LINE-The AC LINE connector mates with a three wire
line cord which provides connections to line voltage. For cor­rect line voltage setting refer to paragraph 7.3.

WARNING
Ground the instrument through a properly
earth grounded receptacle before opera-

tion. Failure to ground the instrument may

result in severe injury or death in the event
of a short circuit or malfunction.

operation. This fuse protects the line and the Model 228 linear
power supply.

F3-Fuse 3 is the output fuse. The fuse is rated at 2OA, 25OV,
normal blow. If this fuse is blown the is no output present on
the output connectors except through the sense connection.

CAUTION
Do not install a fuse with a higher rating
than specified. Instrument damage may oc­cur.

AC LINE

I

Fuses-There are three fuses that are located on the rear pant
Each fuse protects a different circuit of the Model 228.

Fl-Fuse 1 is the linear power supply fuse. The fuse is a SLO­BLO fuse and is rated at 3/4A for 9OV-125V operation and
3/8A for 18QV-25OV operation.

FZ-Fuse 2 is the line power fuse for the switching power sup­ply on the analog board. The fuse is a normal blow fuse rated
at 5A for 9OV-125V operation and 2.5A for 19OV-250V

d

3.9 QUICK DISCONNECT BOARD

Instead of the more common terminals used on other sources
for output connections, the Model 228 output connector,
along with the sense, modulation and current monitor ter­minals, are located on the quick disconnect board. This board
fits through the rear panel into the Model 228 mainframe.
The output, sense, current monitor and external modulation
cables are connected to the terminals on the board of the
Model 228. The card is plugged into the appropriate slot in
the rear panel. When the card is removed from the main­frame, the output, sense, current monitor and external
modulation terminals are disconnected from the mainframe
connections, As a result, the user should never have to come
in contact with a live output. Figure 3-4 shows the quick
disconnect board and the location of each terminal.

Several quick disconnect boards could be used, each with a

unique configuration. In that way, when a particular con­figuration is required, it is simply plugged into the Model 228.
Thus, redundant rewiring of just one quick disconnect board

is avoided. Figure 3-S shows how to install the quick discon-

nect board into the Model 228 mainframe. The Keithley part

number of the quick disconnect board is Model 2286. One quick
disconnect board is supplied with each Model 228.

3-16

Figure 3-4. Quick Disconnect Board

8 CONNECTOR

C ASSEMBLY 500-32

EXTERNAL TRIGG

CONNECTORS

QUICK DISCONNECT BOARD

Figure 3-5. Quick Disconnect Board Installation

3-17

3.10 REMOTE/LOCAL SENSING

The sense (S+ and S-) terminals are located on the quick
disconnect board. The sense terminals are used in the volts

mode. When a load is connected to the Model 228, there
is an IR lead drop between the load and the Model 228.
In some situations the IR lead drop is negligible and does
not need to be taken into consideration. This is where local
sensing may be used.

To configure the quick disconnect board for local sensing,

install the two shorting links as shown in Figure 3-4. The

links connect the sense (S) terminals directly to the output

(OUT) terminals. The load can then be connected to the
two output (OUT) terminals.

In more sensitive applications, the IR lead drop may cause

an intolerable error in the actual voltage delivered to the
load. In this case, the Model 228 could be configured for
remote sensing. Remote sensing compensates for the IR
lead drop by maintaining reguiation at the load instead of
at the output terminals of the Model 228. To configure the

quick

disconnect board for remote sensing, remove the two

shorting links. For remote sensing, connect OUT+ and S+

to the positive side of the load, and connect OLJT- and

S- to the negative side of the load.

CAUTION

Take care to connect the sense terminals

(S+ and S-I to the load with the proper
polarity. Connect S+ to the positive ter­minal and S- to the negative terminal. Im­proper polarity may result in damage to the
instrument.

3.

Data is entered on the right display by pressing the desired
number key. As each digit is entered, the cursor moves one
place to the right until the last digit (least significant) is
reached. Then it is wrapped around to the first digit on the
left (most significant) of the display.

4. Only as many significant digits as necessary need to be
entered. The Model 228 completes the constant with trail­ing zeroes where necessary.

5.

Invalid key presses are ignored. If an invalid key is pressed,
the flashing digit (cursor) remains at the present digit.

6. If an incorrect digit is entered, the complete constant must

be re-entered. The new value may be entered by cycling
the cursor around to the most significant digit. To do this,
repeatedly press any one of the number keys.

7. If too many digits are entered Err is displayed and the pro-

gram is terminated.

8.

Once all the digits of the desired constant are shown on the
display, the constant is entered into the program by press­ing the ENTER key. This applies only to Programs 1 and

3.

Table 38. Summary of Front Panel Programs

Program Operation

:

3

4
5

:

COPY

Sink
IEEE (Set IEEE primary address)
Mod V (Voltage Modulation)
Mod I (Current Modulation)

Test (Diagnostic Self Test)

Reset (Factory Conditions)

3.11 FRONT PANEL PROGRAMS

This section contains instructions necessary for operating the
seven front panel programs of the Model 228. The programs
are activated by pressing the PROGRAM key along with the
DATA key that represents the desired program. The pro­grams do a number of various tasks which are summarized in

Table 3-8.

Program Notes:

1. Each program is entered by pressing the PROGRAM key
followed by the desired program number.

2. After the PROGRAM key is pressed the Model 228
displays the following on the right display.

PRO?

As you have noticed, the question mark is flashing. This is
a prompt for the user to enter the desired program number
(refer to Table
the Model 228 goes into the program selected.

3-18

3-7).

After entering the program number,

3.11.1 Program 1 Copy

Program 1 is used to duplicate the voltage, current, dwell
time data, sink only mode and modulation status of one
memory location into the next memory location. This pro­gram is useful in an application when one to four of the five
parameters required are constant. The variable parameter(s)
is (are) the only one that needs to be changed for each
memory location. For example: Plotting the IV characteristics
of a diode is an example where the current could be set at a
certain level and the dwell time be constant. The voltage
could be programmed to increase O.lV in each successive
memory location. Program 1 could duplicate the current and
dwell time data in each programmed memory location. Only
the voltage would have to be changed for each programmed
memory location.

NOTE
For this example the sink mode and modulation
status are off.

In this case the voltage, current and dwell time parameters are
programmed in the first memory location and Program 1 is
activated. All the data is duplicated into the next memory
location. The next step is to change the voltage of the pro­grammed memory locations to the desired level. The memory
control mode is selected and the START/STOP key is press­ed. The Model 228 outputs the parameters in each memory
location at the programmed rate (dwell time).

Using Program 1 saves many programming steps. Use the
following procedure to duplicate the current and dwell time
of memory location 1 to memory locations 2 through 10.

Required Parameters:

5OOmA

Current Limit
One Second Dwell Time
O.lV to 1V in O.lV steps

If the Model 228 is operating near the maximum dissipation
limit (lOOW), and this is causing the internal temperature to
exceed 9O”C, the sink only program (Program 2) activates as
indicated by the flashing SINK ONLY LED. In this mode the
sourcing capability is reduced. Return to normal operation by
pressing PRO,

2.

For example: Consider charging and discharging a battery.
While charging, the Model

228

sources power. When dis­charging, the Model 228 sinks power. In the sink mode the
Model

228

is an accurate and stable load. When operating the

Model

228

as an active load ensure that the recommended

operating limits of Figure 3-12 are not exceeded.

Press the following keys to enable the sink only program:
PROGRAM,

2.

1. Turn on the Model 228 and allow ten minutes for warm
UP.

2.

Select memory location 1.

3.

Program O.lV for memory location 1.

4. Program 5OOmA for memory location 1.

5.

Program a one second dwell time for memory location 1.

6. Press PROGRAM,l. Duplicates data from one location
into the next location.

7. Repeat step 6 for every location up to location 10.

8. Reprogram the voltage for each memory location. (0.2V
in location 2, 0.3V in location 3, etc.)

9. Press AMPS/SECONDS. Selects the current for display.

10. Press OPERATE/STANDBY.

11. Select SINGLE CYCLE. Press START/STOP.

After the START/STOP key is pressed the Model 228 out­puts the programmed parameters in one second intervals. All

of the memory locations are covered and the cycle stops after
memory location 10. By noting the left display (for each
memory location), the current level is known. The voltage
level is also known. The IV graph could be plotted with this
information. Program 1 saves the user from programming all
three parameters for each memory location.

3.11.2 Program 2 Sink

The sink program allows the instrument to decrease its high
power supply and still operate as an active load. With the
supply reduced, the Model can dissipate full power con-

tinuously at 50°C ambient temperature with no derating.

3.11.3 Program 3 IEEE

Program 3 is used to set the primary address of the Model 228
for IEEE-488 bus operation. The primary address of the
Model 228 is set to 11 at the factory, but it may be set to any
value between 0 and
avoided) via front panel Program 3. This is a convenient
feature that eliminates the cumbersome rear panel switches
that are generally used in other instruments to set primary ad­dress. Note that the primary address of the instrument must
agree with the address specified in the controlIer’s programm­ing language. Program 3 is the only way to change the Model

228's

primary address. The programmed primary address is
briefy displayed as part of the power up cycle, the selft test se­quence and Program 9 sequence.

If other instrumentation is connected to the bus,
be sure that each device has a different primary
address. If this precaution is not observed, er­ratic bus operation may result.

31

(as long as address conflicts are

NOTE

Use Program 2 when the Model 228 is to be used as a high
power load above SOW. By noting the front panel, the state of
the output is known. The front panel COMPLIANCE graph
shows when the Model 228 is operating in the sink mode (ac­tive load). In the sink mode the Model 228 acts as a load and
dissipates power instead of sourcing. The connected external
source and

228

setting indicates that the Model 228 is in the

sink mode.

To initiate Program 3 and change the primary address to 22,
press the following keys:

1. Press PROGRAM (Selects program mode and displays

Pro?).

2. Press 3 (selects Program 3 and displays the following).

IEEE 11

3-19

Where:
IEEE = IEEE indicator
11 = Primary Address

3. Press 2,2,ENTER. This step loads the number 22 onto the
display. Pressing the ENTER key programs the primary
address 22 and reverts the Model 228 to the previous
operating mode.

4. Press PROGRAM,3. This step shows the user that the
primary address has indeed changed to 22.

5. Now that you know how, change the primary address
back to 11.

A. Press PROGRAM,3.
B. Press l,l,ENTER.

- 100%
FULL

SCALE

EXTERNAL MODULATION

1+1ov

3.11.4 Program 4 MOD V

(Modulate Output

Voltage)

This program is used to allow an AC signal to be super­imposed on the output. The modulation signal is applied to
the rear panel external modulation terminals on the quick
disconnect board. Program 4 is activated and then the front
panel MODULATE V LED turns on. Figure 3-6 shows a
graph of operation for the external modulation feature. When
Program 4 is activated Program 5 is disabled.

Use the following procedure to activate Program 4.

1. Connect the external signal source to the external modula­tion connector on the quick disconnect board.

2. Press Program, 4. This step activates Program 4 and turns
on the front panel MODULATE V LED.

3. Program the Model 228 for the desired output.

4. Set the Model 228 to the operate mode.

5. The modulate output is now present on the output connec­tors.

NOTE

Use shielded cables when using external modula-

tion. The shield should be connected to output
LO. Shielded cables help in reducing extraneous
noise.

JIEAS B and C INCREASE THE MAGNITUDE OF THE OUTPUT SETTING
,REAS A and D DECREASE THE MAGNITUDE OF THE OUTPUT SETTING

Figure 3-6. Graph of Operation for External

Modulation

3.11.5 Program 5 MOD I (Modulate Output
Current)

Program 5 is used to allow an AC signal to be superimposed

on the output. The modulation signal is applied to the exter­nal modulation terminals on the quick disconnect board. Pro­gram 5 is activated and then the front panel MODULATE I

LED turns on. Figure 3-6 shows a graph of operation for the
external modulation feature. When Program 5 is activated,

Program 4 is disabled.

Use the following procedure to activate Program 5.

1. Connect the external signal source to the external modula-

tion terminals.

2. Press PROGRAM, 5. This step activates Program 5 and

turns on the front panel MODULATE I LED.

3. Program the Model 228 for the desired output.

4. Set the Model 228 to the operate mode.

5. The modulation signal is now present on the output signal.

3-20

NOTE

Use shielded cables when externally modulating
the output of the Model 228. The shield should
be connected to output LO. Shielded cables help
in reducing extraneous noise.

After the CAL cycle message, the Model 228 reverts to the
previously shown display. For example, if the Model 228 was
displaying + 1.234V then that is the display it reverts to after

the CAL 00 message.

3.11.6 Progrem 6 lest (Diagnostic Self Test)

Program 6 is used to run a test on &ROM, RAM circuitry,
perform auto cal sequence and tests the front panel LEDs.
This test is also performed in the power up sequence. If it is

desired to run the self test without using the IEEE-488 bus,

Program 6 can be used. Use the following procedure to ac-

tivate Program 6.

1. Press PROGRAM. Selects the program mode.

2. Press 6. Initiates the Program 6 test sequence.

Once step 2 is completed the Model 228 performs the follow­ing sequence:

The Model 228 turns on all the segments in the display and
also turns on the rest of the front panel LEDs (e.g. LOCAL,
REMOTE, SINGLE CYCLE, VOLTS, etc). The display
segments are shown as follows:

(+I l3imz-l

This is a display test, the operator can note inoperative
display segments by comparing the display with the above
figure. AI1 the LEDs should turn on if operating correctly.
While the LEDs are on, the Model 228 is performing a cyclic
redundancy check (CRC) of the ROM circuitry. A digital self
test of the RAM circuitry is also being performed at this time.
If the digital self test reveals a problem with the RAM cir­cuitry the Model 228 displays the following.

3.11.7 Program 9 Reset

Program 9 is used to reset the Model 228 to the factory condi­tions. These conditions are the same as the device clear (DCL)
command with one exception. The exception is that all of the

programmed memory locations are cleared of all previous

data. To activate Program 9 use the following procedure:

The sequence for Program 9 is the same sequence as upon
power up.

1. Press PROGRAM, 9. Selects Program 9.

2. All digits and LEDs are turned for a few seconds.

3. The Model 228 displays the software revision level.

4. The Model 228 displays the primary address.

5. The Model 228 reverts to the VOLTS and AMPS display
and memory location I.

Once the VOLTS and AMPS display show zero, the Model
228 is reset to the factory on conditions.

3.12 LOADS

The Model 228 is capable of delivering power to a load or
sinking (dissipating) power. Either mode depends on the pro­gramming of the instrument. If the actual voltage and current
have the same polarity (both positive or both negative), the
Model 228 is operating in the source mode. The front panel
COMPLIANCE graph displays the state of the Model 228

(source or sink).

If the CRC reveals a problem with the ROM circuitry the

Model 228 displays the following.

I+ (+

I I 1

If all tests pass, the Model 228 displays the following:

,

In the source mode, the Model 228 must have a device in
which to deliver the programmed power. This device is
generally known as the ‘load.” The load stores or dissipates

the Model 228 output power. The load must be rated to han-

dle the programmed output power of the Model 228. If the

load is not properly rated, damage may result. There are

three categories of loads: resistive, capacitive and inductive.

These different loads all have their own unique parameters.

Each type of load contains in some small amount each of

these parameters. In general, however, loads are considered

to be mostly one parameter, either resistive, capacitive or in-

ductive. Each type of load is described in the following

paragraphs.

3-21

The Model 228 is a constant voltage/constant current source.
The load determines which parameter is constant, either
voltage or current. For example, if the load is of high im­pedance, the voltage is controlled with the impedance deter­mining the

amount

of current. If the load is of low im­pedance, the current is controlled with the impedance deter­mining the voltage. For example: If the Model 228 is pro­grammed to 1OV and lOA, a load of more than IQ controls
the current, and a load of less than ln controls the voltage.

I=lOV/2~=5.OOA (2Q load, current limits to 5A)
V=lOAX0.5Q=5.OOA (0.5n load, voltage limit of 5V)

R > VSEl-TING

--.
ISETTING

then, the Model 228 operates as a voltage

source.

VSE?TING then the Model

R<

228

operates as a current

‘SEnING source.

Where:
V = The voltage setting on the Model 228.
I = The current setting on the Model 228.

= User load.

R

3.121 Load Line Description

The information contained in Figure 3-7 is a general descrip­tion only. Refer to other sections of this manual for detailed
information.

3-22

223A OPERATES AS A
CONSTANT CURRENT
LOAD

-1

OUADRANTZ 1

STANDBY LOAD -+

LINE (Ok’, OA) :

DUADRANT 3

223A OPERATES AS A
CONSTANT VOLTAGE
SOURCEWTHA
CURRENT LIMIT OF

+I SElTlNG

I

- z

QUADRANT 1

QUADRANT4

2?3A FRONT PANEL %fTlNGS

+vsEmNG ~SEITING

J

Z?3A OPERATES AS A
CONSTAM CURREFIT
SOURCE Wi-lH A
COMPLIANCE OF

2?3A OPERATES AS A
CONSTANT CURRENT

22BA OPERAES AS A
CONSTANTVOLTAGE
LOAD

QUADRANT 1:
This quadrant is used for normal operation. The Model 228A will source positive
voltage and current.

The Model 228A is sourcing power to a load.
Since V=IxR, the combination of load R and the Mode1 228A settings will deter-

mine if the Model 228A is operating as a constant current or constant voltage
source.

The Model 228A will maintain a constant voltage output as long as
Gm,.w >VsmmdRm..
The Model 228A will maintain a constant current option as long as
Vs.-,x0 > I,,P,o/R,oA,.
Standby mode is a setting of 0 volts and 0 amps.

QUADRANT 2:
This quadrant is used for general constant voltage load or constant current load

applications.
The Model 22i!A is dissipating (sinking) power from an external device.
The Model 228A will maintain a constant voltage across its terminals as long as

the external device’s current into the Mode1 2281% is less than the Model 228.4’s
current setting.

The Model 228A will operate as a constant current load as long as the external
device’s voltage is greater than the Model 22&A voltage setting.

Operating Note: Rx most applications, the Model 228A will be operated in
quadrant 1 (source) or quadrant 2 (sink). To operate as a sink in quadrant 2, the
polarity of the Model 228A and the external source must be the same. That is,
external source positive must be connected to Model 228A positive. Whether the
Model 228A operates as a source or as a sink depends on the voltage value of
the external source and the programmed voltage of the Model 228A. If the voltage

In standby mode, the Model 228A will appear to be an open circuit.
NOTE: For operating ln this quadrant the polarity of the Model 228As voltage set-

ting and the polarity of the external device’s voltage must be the same.
QUADRANT 3:

Thii quadrant is not on the positive load line shown above. If the Model 228A
were set to -V and -I the Model 22Ws load lime would then cross this quadrant.

QUADRANT 4:
This quadrant is used for a constant voltage load on a current source.

The Model 228A is dissipating (sinking) power

from

an external device.

The Model 228A will maintain a constant voltage across its terminals as long as
the external device’s current is greater than or equal to the Model

228Ks

current

setting.
In standby mode, the Model 22&4 will appear to be a short circuit.
NOTE: For operation ln thii quadrant fhe polarity of the Model 228Ks voltage

source and the polarity of the

external

device’s voltage must be opposite. It ls im­portant to note that current is not liited while the Model 228A is operating ln
quadrant 4 and should not be used to discharge batteries. Excessive current may
cause damage to the Model 228A and/or the external source. Quadrants 1 and
2 should normally be used to charge and discharge storage

elements,

such as bat-

teries and capacitors.

of the external sounze ls equal to or less than the programmed voltage of the Model
228A, then the Model 228A will operate as a source. Current will flow out of the
Model 228A. Conversely, if the voltage of the external source exceeds the pro­grammed voltage of the Model 228A, then the Model 228A will operate as an ac­tive sink. Current will flow into the Model 228.4.

Figure 3-7. Load Line (Positive Line Shown)

3-23

3.12.2 Resistive Loads

capacitance and inductive loads. Reactive loads require cer­tain considerations that are listed as follows:

Using a resistive load, the Model 228 is capable of delivering a
constant voltage or constant current up to the programmed
compliance. With a resistive load as shown in Figure 3-8, the

voltage developed across the load resistance is defined as VL

= IL x RL.

Where:

VL = The voltage developed across the load.

= The current through the load.

IL
RL = The load resistance.

If the voltage is programmed to less than the voltage VL, then
the Model 228 is voltage controlled. If the current is pro­grammed to less than the current IL, then the Model 228 is
current limited.

The power delivered to the resistive load must not exceed the
power rating of the load. If excessive power is delivered to the
load, damage may result. For example, if the load is a resistor
and is rated at lOW, then the power must not exceed 1OW.
This means that if the Model 228 voltage is programmed for
lOV, then the current must not be programmed for more than
1A (1OV X 1A = 1OW) or 1OA and 1V (10A X 1V = low).
In any case, the voltage/current combination must not exceed
the limits of the load. Otherwise, the load may be damaged.

QUICK

DISCONNECT

BOARD

1. The user must supply the necessary circuitry to limit the
voltage across inductors.
selected voltage range may damage the instrument. During
power on, calibration, low or missing line power, the
Model 228 disconnects the output with relays. This could
cause uncontrolled arcing along the inductive circuit. Refer
to Figure 3-9 for suggested clamp circuit.

2. Capacitors and inductors require proper discharging
before touching any output wiring. This is because in the
standby mode or when power failures occur, the reactive
circuit could be left with a full charge.

3. Settling times are longer for large reactive loads, as a result
overshoot and ringing may occur. Damping resistors could
be used to improve the response. Refer to Figure 3-9 for
damping resistor circuits.

Voltage above 101% of the

3.q2.4 Inductive Loads

In general, in the constant current mode the output load
should be resistive. However, a small amount of inductance
in the load can be tolerated, but only if the inductive reaction
voltage, L $ , is limited to less
voltage for each range. Figure 3-9 shows a suggested method
of limiting the inductive reaction voltage. The zener diodes

must be rated for each current range as listed in Table 3-9. An

inductive load may not be obvious. Loads that contain wire­wound resistors or relay coils, (etc.) are inductive and could
produce damaging voltage spikes. Figure 3-10 shows induc-

tive load connections.

than

the maximum compliance

MODEL 228 ‘I -“l:h

C

’ I

t

‘L

-7

I

Figure 3-8. Resistive Load Connections

3.12.3 Reactive Loads

The Model 228 is stable for an exceptionally wide range of

3-24

VL

1

LOAD

(RESISTIVE)

VL = IL RL

CAUTION

In the current function, if the output load
connected to the Model 228 is inductive,
limit the inductive reaction voltage to less
than the maximum compliance voltage for
that range. Otherwise, instrument damage

may occur.

Some examples of inductive loads include:

1. Relay Coils

2. Electric Motors

3. Wirewound Resistors

4. Transformers

5. Solenoids

MODEL 228

8.

MODLE 228

MODEL 228 1

r

mm-

LOAD

1'

LOAD

C.

---

MODEL 228

E.

OTE SE-ITLING TIMES INCREASE WITH NON RESISTIVE LOADS.

I-

+
1

LOAD

Figure 3-9. Limiting Inductive Reaction Voltage

LOAD

“MAX = IMAX “R

D.

MODEL 228

R

DAMPING

RESISTOR

/\ LOAD

F.

3-25

LOAD RESISTANCE

Some examples of capacitive loads include:

1. Capacitor

2. Power Supplies

INDUCTANCE (L)

Figure 3-10. Inductive Load Connection

Table 3-9. Maximum Inductive Reaction

Range

MaxLdt

3.12.5 Capacitance Loads

LOAD

Voltage

di

II

AZ

LOAD

CAPACITANCE

T

Figure 3-11. Capacitive Load Connections

3.12.6 Load Regulation

Load regulation is an important parameter that is to be con­sidered when using the Model 228 as a current source or a
voltage source. Load regulation may be computed by the
following two methods:

1. As a Current Source:

When a capacitive load is connected to the Model 228 output,
the Model 228 delivers a constant current until the voltage
developed reaches the programmed compliance voltage, in­strument voltage compliance limit or the working voltage of
the load. The voltage charges to a maximum Vc with the
following equiation:

vo = $ j I 2 up to Vc (maximum)
Figure 3-11 shows the Model 228 connected to a capacitive
load. If the Model 228 compliance voltage is changed to a

smaller value than is charged on the capacitor, the capacitor
starts discharging into the Model 228. For this period, the
Model 228 is in the sink mode. Notice the front panel COM­PLIANCE graph; it indicates the Model 228 is in the sink
mode. When the capacitor charge voltage reaches the lower
compliance voltage, the Model 228 returns to the source
mode.

3-26

0

*I

Load Regulation (Current Mode) = Ram X 100%

ROUT __ COUT

AVOLJT

I

T

“OUT

Ω

Ω

2. As a Voltage Source:

I

+

+V

OUT

-

Load Regulation (Voltage Mode) =

-----------------------------------------­V

100%×

∆I

•[]

OUTROUT

As an example; consider the 1A range and 100V compliance.

OUT

OUT

I

5

.

100%

100V[]

------------------

5

10

Ω

-----------------­1A

100%× 0.1%==×

The R

specification is 10

OUT

Load Regulation=

∆V

[]

----------------------­R

------------------------

3.12.7 Charging and Discharging
Electrochemical Cells

The Model 228A can be used to charge and/or discharge
electrochemical cells. When configured to charge a cell, the
Model 228 operates as a source; when configured to dis­charge a cell, it operates as a sink.

Connections to charge and discharge a cell are shown in
Figure 3-18. In general, charge the cell by configuring the
Model 228A to operate as a source using appropriate voltage
and current levels. For example, to charge a 10V cell, set the
Model 228A to source +10V at an appropriate charging
current level (i.e. 0.1A). When the cell reaches +10V, the
charging current stops (0A).

To discharge the cell, set the Model 228A to 0V with current
at the desired level. The cell is completely discharged when
the discharge current level reaches 0A.

CAUTION
NEVER change polarity on the Model 228A
to discharge an electrochemical cell.
Doing so will cause a large current surge
that will damage the power supply of the
Model 228A. ALWAYS allow the cell to dis­charge to 0V before changing polarity to
charge the cell in the opposite direction.

For example, if after charging the cell to
+10V you change the polarity of the source
to -10V, the resultant current surge will
damage the Model 228A.

If your test requires charging and discharging electro­chemical cells in both directions, use the following general
procedure to avoid damaging the Model 228:

1. Charge (+) — Charge the cell using the appropriate +V
and +I levels.

2. Discharge (+) — Discharge the cell by setting the source
to 0V and waiting for the cell to completely discharge
(cell at 0V).

3. Charge (-) — Charge the cell in the opposite direction
using the appropriate -V and -I levels.

4. Discharge (-) — Discharge the cell by setting the source
to 0V and waiting for the cell to completely discharge
(cell at 0V).

To avoid damage to the Model 228A, the following relation­ship must exist between charge/discharge current and time:

|I

|t

> |I

|t

d

c

c

where: I

= discharge current

d

= discharge time

t

d

= charge current

I

c

= charge time

t

c

d

This expression states that the product of discharge current
(I

) and discharge time (t

d

of charge current (I

c

) must be greater than the product

d

) and charge time (t

). If it is not, damage

c

to the Model 228 will result.

If charge current (I

) and discharge current (I

c

) of the cell are

d

the same, then the expression can be simplified as follows:

t

>t

d

c

This simply states that if charge and discharge current are the
same, you must ensure that the discharge time of the cell is
greater than the charge time.

3.13 OPERATING EXAMPLES

The following examples give specific instructions on how to
use the Model 228 in various configurations. These examples
are written with the first time user in mind. However, refer to
the front and rear panel control descriptions in Tables 3-2 and
3-3 before proceeding with these examples. Note all of the
warning and cautions associated with these examples. Take
the time to read them and, most of all, to understand them.

3.13.1 Example 1: 10.00V, 10.00A Output

In this example, the Model 228 will be programmed for
+10.00V and +10.00A. These values were chosen to keep the
numbers simple (10V/10A=1
can concentrate on the front panel instead of a cumbersome
number calculation. The 10V range has a maximum compli­ance current of 10A; conversely, the 10A range has a maxi­mum compliance voltage of 10V. Refer to the specifications
that precede Section 1. In this example, voltage and current
are limited to 10.00V and 10.00A by the user; and in this case,
the instrument limits these values. This information is stored
in memory location 1.

). With these values, the user

3-27

V

Ω

Ω

Ω

Ω ×

This example does not step the user through the selection of a
memory location. Memory location 1 is selected upon power
up and that is sufficient for this example. Since there is just
one memory location used in this example, programming the
dwell time is not covered. Later examples explain the use of
memory locations.

The Model 228 is a constant voltage/constant current
(CV/CC) source. This means that the voltage and current are
programmed into the instrument. The output of voltage or
current depends on the load. If the load is of high impedance,
the voltage is controlled with the impedance determining the
amount of current drawn from the source. If the load is of
low impedance, the current is controlled with the impedance
determining the voltage. The maximum value of voltage or
current (up to rated specifications) is defined by the user. The
user defines these parameters when programming the volt­age and current values. In this example:

If the load is less than 1
LED just above the + (+I

, the source controls current. The

SOURCE

) on the front panel COMPLI-

ANCE graph is on.

If the load is greater than 1
LED just to the right of the +V (+V

, the source controls voltage. The

SOURCE

) on the front panel

COMPLIANCE graph is on.

For example: A 2 Ω load results in a current of 5A (voltage is
controlled by the Model 228).

I = 10V

= 5.00A

2

A 0.5 Ω load results in a voltage of 2.5V (current is controlled
by the Model 228).

V = 0.5

R

If then, the Model 228 operates as a voltage source.

If then, the Model 228 operates as a current source.

R

10A = 5.00V

SETTING

-------------------------->
I

SETTING

V

SETTING

--------------------------<

I

SETTING

Where: V = The voltage setting of the Model 228.

I = The current setting of the Model 228.
R = User Load

Also, in the operate mode, the display shows the actual
parameter value. For example, if 10V and 10A are pro­grammed and the load is drawing 7.5A, then 7.50A is dis­played on the right display (right display must be in amps
display mode).

To program the Model 228 for 10.00V, 10.00A, use the follow­ing procedure:

CAUTION
This example outputs 100W. Make sure
that the connected load is rated to at least
100W. Otherwise, damage to the load may
occur.

1. Turn on the Model 228 and allow ten minutes for warm
up.

WARNING
Do not operate the instrument with the top
cover and/or the bottom cover removed.
Lethal potentials exist throughout the
Model 228 mainframe. The covers must
also be in place to allow proper airflow
through the instrument. If proper airflow is
impeded, the instrument may overheat.

NOTE

Upon power up, memory location 1 is selected.

2. Program the desired voltage value. There are two meth­ods to do this and both are given as follows:

Method 1: Program Desired Voltage Value

A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the left display is

selected. The selected display is depicted by the
flashing bright digit.

NOTE

During the edit mode, if nothing happens on the
front panel for approximately 20 seconds, the
Model 228 cancels the edit mode and returns the
display to the previous conditions.

C. Press the left or right key to select the modify digit.

The left and right keys are indicated by the arrows
on the front panel. The modify digit is depicted by
the flashing bright digit.

D. Press the increment or decrement key to modify the

voltage value. The output tracks the display when
using the increment or decrement keys. The incre­ment/decrement keys are indicated by the up/
down arrows on the front panel.

Method 2: Program Desired Voltage Value

A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the left display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, 0, .0, 0.

D. Press ENTER.

3. Program the desired current value. Like the voltage
value, this can be done in one of two methods. Both
methods are given as follows:

Method 1: Program Desired Current Value

A. Press the AMPS/DWELL TIME key to display cur-

rent (AMPS LED on).

B. Press the SELECT key until the display on the right

is selected. The selected display is depicted by the
flashing bright digit.

3-28

Ω

•

×

×

C. Press the left or right keys (these keys are indicated

by the arrows on the front panel) to select the modify
digit. The modify digit is depicted by the flashing
bright digit.

D. Press the increment/decrement keys to modify the

current value. The output tracks the display when
using the increment/decrement keys.

Method 2: Program Desired Current Value

A. Press the AMPS/DWELL TIME key to display cur-

rent (AMPS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, 0, ., 0, 0.

D. Press ENTER.

4. Connect the appropriate load. For this example, the load
must be rated at least 100W.

5. Press OPERATE/STANDBY to place the instrument in
the operate mode. In the operate mode, the source value
is present on the output terminals.

After step 5 is completed, the Model 228 outputs the voltage
and current to the connected load. This simple example is
designed to set the Model 228 to output a source value. The
next example sets the Model 228 to output 100V, 1A.

3.13.2 Example 2: 100V, 1A Output

This example will program the Model 228 to output a value
of 100V, 1A. The maximum current compliance of a 100V
range is 1A; conversely, the 1A range has a maximum voltage
compliance of 100V. Refer to the specifications that precede
Section 1. Like Example 1, this example does not explain the
use of memory locations which will be discussed later.

Again, the output value depends on the load. If the load is of
high impedance, the value is voltage controlled. If the load is
of low impedance, the value is current controlled. A compari­son between the Model 228 and a battery is a simplified way
of understanding the load of a voltage/current source. As an
example, assume a battery is rated at 1.5V and 1A/hour. If
the battery has a load of 1k

1.5V. Therefore, the current output is limited by the load. The
same is true for the Model 228. If the load is of high imped­ance, the load determines the current. If the load is of low
impedance, the load determines the voltage.

When voltage is controlled by the Model 228,
the load determines the current by Ohm’s law
I = V/R. When current is controlled by the
Model 228, the load determines the voltage by
Ohm’s law, V = I

This example is designed to allow the user to become familiar
with the front panel operation of the Model 228. It illustrates
some basic operating methods of the Model 228.

, the battery outputs 1.5mA at

NOTE

R.

WARNING
This procedure outputs a dangerous
potential of 100V up to 1A. Take care not to
come into contact with the live output, as
personal injury or death may occur.

CAUTION
This example outputs 100W. Make sure the
load is rated for at least 100W. Otherwise,
damage to the load may occur.

In the operate mode, the display shows the actual parameter
value. For example, if 100V and 1A are programmed and the
load is drawing 750mA, then .750A is displayed on the right
display. The right display must be in the amps display mode
in order to display the current.

The Model 228 operates as a voltage source when the follow­ing condition occurs: V < I

The Model 228 operates as a current source when the follow­ing condition occurs: V > I

Where: V = The voltage setting of the Model 228.

I = The current setting of the Model 228.
R = User Load.

1. Turn on the Model 228 and allow ten minutes for warm
up.

Upon power up, memory 1 is selected.

2. Program the desired source. There are two methods to
do this. Both are given.

Method 1: Program Desired Source

A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the left display key is

selected. The selected display is depicted by the
flashing bright digit.

C. Press the left or right key to select the modify digit.

The left and right keys are indicated by the arrows
on the front panel. The modify digit is depicted by
the flashing bright digit.

D. Press the increment or decrement key to modify the

current source value. The output tracks the display
when using the increment/decrement keys to mod­ify the display. The increment/decrement keys are
indicated by the up and down arrows on the front
panel.

Method 2: Program Desired Source

A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, 0, 0, ., 0.

D. Press ENTER.

R.

R.

NOTE

3-29

3. Program the desired current value. This may be done by
one of two methods. Both methods are given.

Method 1: Program Desired Current Value

A. Press the AMPS/DWELL TIME key to display the

current (AMPS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press the left or right key to select the modify digit.

The left and right keys are indicated by arrows on
the front panel. The modify digit is depicted by the
flashing bright digit.

D. Press the increment or decrement key to modify the

current value. The output tracks the display when
using the increment/decrement keys.

Method 2: Program Desired Current Value

A. Press the AMPS/DWELL TIME key to display cur-

rent (AMPS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, ., 0, 0, 0.

D. Press ENTER.

4. Connect the appropriate load. The load must be rated for
at least 100W.

NOTE

The output load must be non-inductive. A small
amount of inductance in the load can be toler-

ated if the inductive reaction voltage, L , is
limited to less than the compliance voltage of

that range. Refer to paragraph 3.9.2.

5. Press the OPERATE/STANDBY key. This step places the

1.00A source current on the output terminals.

di

-----­dt

WARNING
The completion of step 5 outputs a dan­gerous potential. Make sure the load is
properly rated. Do not come into contact
with the live output as personal injury or
death may occur.

After step 5 is completed, 100V at 1A is delivered to the out­put connector and therefore, is available to the load. The
actual voltage drop and current output depends upon the
value of the load. This simple example is designed to set the
Model 228 to 100V at 1A to a predetermined load. In the next
example, the user will set the Model 228 to output three sepa­rate source values in succession.

3.13.3 Example 3: 1V, 10A, 1sec; 10V 10A
2sec; and 100V, 1A, 3sec Output in the
Continuous Memory Control Mode

This example will set the Model 228 to output three separate
source values in succession. This could be used to test certain

parameters of a resistor. The higher voltage could be used to
test the voltage coefficient of the resistor. The higher current
could be used to test the power rating of the resistor. The
accuracy could also be verified by using the Model 228 as an
accurate voltage source. The parameters may vary for this
type of application. The parameter values chosen represent
several ranges of the Model 228.

In order to obtain the three source values, program the
desired values into the memory locations. Each memory loca­tion contains five distinct parameters that make up the mem­ory location: Voltage, Current, Dwell Time, Modulation (V or
I) and Source or Sink mode. Each parameter must be pro­grammed into each memory location.

After the source values are entered into the memory loca­tions, the user must select the desired dwell time. The dwell
time is the time spent on a specific memory location before
moving to the next location. After the dwell time is entered,
the modulation mode must be entered. The modulation
shows the user that Model 228 is in either current or voltage
modulation. Then the last parameter (source or sink) must be
entered. The order of programming these five parameters
does not matter, as long as all five are programmed into the
memory location.

This example may be used as a model for storing several (up
to 100) source values. Up to 100 unique values may be stored
in the Model 228. All of the information stored in the memory
locations (Voltage, Current and Dwell Time, Source/Sink and
Modulate V or I) is battery backed up. This means that if the
instrument is powered down, the information is still valid.
The stored parameters remain as is until they are changed by
the user. Before beginning the example, read the following
outline. The outline gives a short description of the example.
The main parts of the example are sectioned off to show the
complete example in a simplified form. The actual example
follows this short outline.

1. Turn the instrument on.

2. Select memory location 1.

3. Program the desired voltage of memory location 1.

4. Program the desired current of memory location 1.

5. Program the desired dwell time of memory location 1.

6. Program either source or sink for memory location 1.

7. Program modulate V or I for memory location 1.

8. Select memory location 2.

9. Program the desired voltage of memory location 2.

10. Program the desired current of memory location 2.

11. Program the desired dwell time of memory location 2.

12. Program either source or sink for memory location 2.

13. Program modulate V or I.

14. Select memory location 3.

15. Program the desired voltage for memory location 3.

16. Program the desired current for memory location 3.

17. Program the desired dwell time of memory location 3.

3-30

18. Program either source or sink for memory location 3.

19. Program modulate V or I for memory location 3.

20. Select memory location 4.

21. Program the dwell time of memory location 4 to zero.

22. Select memory location 1.

23. Select the continuous memory control mode.

24. Connect appropriate load.

25. Select the operate mode.

26. Press the START/STOP key.

WARNING
Memory location 3 contains a lethal poten­tial of 100V and a current of up to 1A. Take
care not to come into contact with a live
circuit that may cause personal injury or
death.

NOTE

There are two methods of programming values
into the Model 228. Examples 1 and 2 explain in
detail each method. In this example, data keys
method is used.

1. Turn on the Model 228 and allow ten minutes for warm
up.

NOTE

Upon power up, memory location 1 is selected.

2. Select memory location 1.

A. Press the VOLTS/MEMORY STEP key to display the

present memory location (MEM STEP LED on).

B. Press the SELECT key until the left display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, ENTER.

3. Program the desired voltage value.

A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the left display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, ., 0, 0, 0, ENTER.

4. Program the desired current value.

A. Press the AMPS/DWELL TIME key to display cur-

rent (AMPS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, 0, ., 0, 0, ENTER.

5. Program the desired dwell time value.

A. Press the AMPS/DWELL TIME key to display the

dwell time (SECONDS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, ., 0, 0, 0, ENTER.

6. Program Modulation (V or I). Press Program 4 to modu­late V or Program 3 to modulate I. Notice that the appro­priate LED turns on.

7. Program source or sink.

A. Press Program 2 to enable the sink mode. Notice that

the appropriate SINK LED turns on.

B. If source mode is desired, turn off the sink program.

8. Select memory location 2.

A. Press the VOLTS/MEMORY STEP key to display the

memory location (MEM STEP LED on).

B. Press the SELECT key until the left display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 2, ENTER.

9. Program the desired voltage value for memory location 2.

A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the left display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, 0, ., 0, 0, ENTER.

10. Program the desired current value for memory location 2.

A. Press the AMPS/DWELL TIME key to display the

dwell time (AMPS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, 0, ., 0, 0, ENTER.

11. Program the desired dwell time for memory location 2.
A. Press the AMPS/DWELL TIME key to display the

dwell time (SECONDS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 2, ., 0, 0, 0, ENTER.

12. Program modulate V or I. Press Program 4 to modulate V

or press Program 5 to modulate I. Notice that the appro­priate LED turns on.

13. Program source or sink.
A. Press Program 2 for sink mode. Notice that the SINK

LED turns on.

B. If source mode is desired, turn off sink mode.

14. Select memory location 3.
A. Press the VOLTS/MEM STEP key to display the

memory location (MEM STEP LED on).

B. Press the SELECT key until the left display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 3, ENTER.

15. Program the desired voltage value for memory location 3.

A. Press the VOLTS/MEMORY STEP key to display

volts (VOLTS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, 0, 0, ., 0, ENTER.

3-31

16. Program the desired current value of memory location 3.
A. Press the AMPS/DWELL TIME key to display the

dwell time (AMPS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 1, ., 0, 0, 0, ENTER.

17. Program the desired dwell time for memory location 3.
A. Press the AMPS/DWELL TIME key to display the

dwell time (SECONDS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 3, ., 0, 0, 0, ENTER.

18. Program modulate V or I. Press Program 4 to modulate V

or press Program 5 to modulate I. Notice that the appro­priate LED turns on.

19. Program source or sink.
A. Press Program 2 for sink mode. Notice that the SINK

LED turns on.

B. If source mode is desired, turn off sink mode.

20. Select memory location 4.
A. Press the VOLTS/MEM STEP key to display the

memory location (MEM STEP LED on).

B. Press the SELECT key to select the left display for

modification.

C. Press 4, ENTER.

21. Program the dwell time to zero.
A. Press the AMPS/DWELL TIME key to display the

dwell time on the right display (SECONDS LED on).

B. Press the SELECT key until the right display is

selected. The selected display is depicted by the
flashing bright digit.

C. Press 0, 0, .0, 0, ENTER.

22. Select memory location 1.

23. Press the CONTINUOUS key. This step places the Model

228 in the continuous memory control mode.

24. Connect the appropriate load. The load must be rated at

least 100W.

25. Press OPERATE/STANDBY to place the source value at

the output terminals.

CAUTON
An output transient a few milliseconds in
duration may occur when placing the
Model 228 in OPERATE while it is in the
process of a single or continuous memory
control cycle. This transient can be as high
as full scale of the range it is currently on
and may cause damage to external cir­cuitry. To avoid this potentially damaging
transient, always make sure the Model 228
is in OPERATE before starting the memory
control cycle. If a memory control cycle is
already started, it can be stopped by
pressing the MEMORY CONTROL button.

NOTE

Before placing the instrument in the operate
mode, take the time to read and understand the
safety precautions described in Section 2. These
precautions are presented for user safety.

26. Press the STOP/START key to start the memory control
mode.

WARNING
Memory location 3 contains a lethal poten­tial. Do not come into contact with the live
output. Personal injury or death may occur.

After step 26, the Model 228 continuously cycles through the
programmed memory locations. Since the OPERATE LED is
on, the source values are present at the output terminals.

The single step memory control mode allows the user to step
through the programmed memory locations one at a time.
Each time it is desired to advance to the next programmed
memory location, the user need only press the START/STOP
button. The START/STOP LED turns on for the duration of
the programmed dwell time and then turns off. When the last
programmed memory location is selected (memory location
3, in this example), pressing the START/STOP key reverts the
instrument to memory location 1. This is true for the last pro­grammed location as long as the next location has a zero
dwell time.

The single cycle memory control mode allows the user to
cycle through all the programmed memory locations one
time. To start the single cycle mode, press the START/STOP
key. Once the single cycle mode is activated, the Model 228
starts from the next programmed memory location and
advances to each programmed memory location. The instru­ment remains at each memory location for the programmed
dwell time and then advances to the next location. After the
dwell time of the last programmed memory location, the
START/STOP LED turns off and the single cycle mode is
ended.

The continuous memory control mode allows the user to
cycle through all of the programmed memory locations con­tinuously. To start the continuous memory control mode,
press the START/STOP key. To stop the continuous memory
control mode, press the START/STOP key a second time.
When the START/STOP key is pressed the second time, the
continuous mode stopped at the present memory location.
Once the continuous memory control mode is activated, the
Model 228 advances to the next memory location. The instru­ment remains at this location for the programmed dwell time
(dwell time can vary for each location) and then advances to
the next memory location. The cycle continues up to and
including the last programmed memory location (or memory
location with a zero dwell time) and then reverts to memory
location 1. At this point, the cycle starts over again and keeps
repeating until the START/STOP key is pressed and the
instrument is turned off or another memory control mode is
activated.

3-32

Memory Control Mode Notes

1. The START/STOP key has three functions:
A. Start the memory control mode.

B. Stop the memory control mode.
C. Advance to the next memory location in the single

step mode.

2. The single step mode allows the user to step through the

programmed memory locations one at a time.

3. The single cycle mode allows the user to cycle through

the programmed memory locations one at a time.

4. The continuous mode allows the user to cycle through

the programmed memory locations continuously.

5. Dwell time is the time spent on one memory location.

6. An entry of zero for the dwell time for any memory loca-

tion reverts the instrument to memory location 1. (20msec
to 1000sec in 1msec steps. (1sec steps in 1000sec range).

7. Each memory location contains five distinct parameters:
A. Voltage

B. Current
C. Dwell Time

D. Modulate V or I

E. Source or Sink

8. There is a total of 100 memory locations.

9. The memory control mode may be started by one of

three methods.

A. Pressing the START/STOP key.

B. Applying proper external trigger.
C. Sending the proper command over the IEEE-488

bus. This means that the PROGRAM command (P0,
P1 or P2) is selected and the appropriate trigger
command is implemented. For example, if the T0
(Start on TALK) mode is selected, and the instru­ment is addressed to talk, the selected memory con­trol mode is initiated.

10. When the continuous or single cycle memory control
modes are running, stopping the sequence halts the
instrument at the present memory location. Continuing
the sequence starts at the next memory location.

Examples 1, 2 and 3 all deal with the Model 228 programmed
as a source. This means that the Model 228 outputs voltage
and current. Observe the front panel COMPLIANCE graph
and notice that the Model 228 is operating in the source mode
(+V and +I LEDs are turned on one at a time). The source
mode is depicted by the voltage and current having the same
polarity. The polarity could be either positive or negative, it
does not matter as long as the polarity is the same for the
voltage and the current, the instrument is operating in the
source mode.

3.13.4 Example 4: Model 228 as an Active

Load (Current Sink)

This next example deals with the Model 228 operating in the
sink mode. In the sink mode of operation, power is delivered

to the Model 228 by an external source. As can be seen by the
graph and/or Figure 3-12, when voltage and current both
have the same sign (positive or negative), the Model 228 is in
the source mode.

If the voltage or current have different polarity, then the
Model 228 is in the sink mode. In the sink mode, the Model
228 accepts power (dissipates) instead of providing the
power. Operating the Model 228 as an active load dissipates
power up to the limits shown in Figure 3-12. Of course, the
limits shown in Figure 3-12 must not be exceeded.

CAUTION
When the Model 228 is used in the sink
mode, that is, power is delivered to the
Model 228 by an external power source.
Care should be taken to limit the power
delivered to the Model 228 as shown in
Figure 3-12. If power dissipated within the
Model 228 exceeds these limitations, over­heating and damage to the instrument may
occur. For example, if the external power
source is capable of delivering greater
than 1A, then the voltage across the Model
228 output terminals must be less than
100V (100V x 1A = 100W).

WARNING
During the sink mode of operation, the
Model 228 and the external source must
have the same voltage polarity in order for
the current limiting to operate. Otherwise,
the output fuse (20A) is the current limit.

The COMPLIANCE graph on the front panel provides the
user with the location of where the Model 228 is operating.
By noting the front panel COMPLIANCE LEDs, four parame­ters concerning the output are known:

1. The polarity of the voltage.

2. The polarity of the current.

3. The controlling function (voltage or current).

4. The operating mode (sink or source).

For example: If the LED just above the +I (+I
is turned on, then:

1. The polarity of the voltage is positive because it is in the
+V half.

2. The polarity of the current is positive because it is in the
+I half.

3. The controlling function is current because the line for
that LED goes through the +I axis, the current is constant
and the voltage is the parameter that varies. For lines
intersecting the voltage axis, the voltage is constant and
the current is the parameter that varies.

SOURCE

) symbol

3-33

4. The instrument is operating as a source because the voltage
and the current both have the same polarity (positive).

(The LED is in a “source” quadrant,)

+v

+V LIMIT OF RANGE

RECOMMENDED

ENABLING SINK

PROGRAM

ABOVE 5A

-I
OF RANGE

-I LIMIT

AND 5V

+ I LIMIT

RECOMMENDED
ENABLING SINK

PROGRAM
ABOVE 5A

AND 5V

-V LIMIT OF RANGE

OF RANGE

+I

-v

Figure 3-12. Model 228 Recommended Operating

Limits

Figure 3-13. Model 228 as an Active Load

NOTE

The external source connected to the Model 228
output determines whether the Model 228
operates as an active load. In other words, the
Model 228 operates as an active load whenever
its output is connected to a voltage source that
exceeds the programmed output voltage of the
instrument.

The following procedure programs the Model

25V, 1OOmA = (2.5W).

228

to sink

In

this example,

the Model 228A accepts (dissipates)
power from the battery voltage. In the sink mode, the
Model 228A is an active load that is both constant and ac­curate. The configuration is shown in Figure 3-13. Make
sure the polarity of the connections are correct before plac­ing the Model 228A in the operate mode.

Using the SINK program (front panel Program 2)

reduces

the internal power dissipation within the Model 228A. The

sink only mode activates automatically if the internal
temperature of the instrument reaches 90°C. Normally,
this only occurs at high ambient temperatures and high
power sink operation.

NOTE

The sink only mode is only useful on the

range, between 5V and 1OV. The sink only pro­gram limits sourcing capability to approximately

1.5A

and also limits sink capability when

voltages are less than three volts.

1OA

1. Turn on the Model 228 and allow ten minutes for warm
up*

NOTE

Upon power up, memory location 1 is selected.

2. Program the desired voltage value. In this example, the

voltage must be positive.
A. Press the VOLTS/MEMORY key. This step displays

the present voltage value on the left display.

B. Press the SELECT key. This step selects the left display

for modification.

C. Press 2, 5, ., 0, 0, ENTER.

3.

Program the desired current value. In this example, the

current is programmed as positive. The external source
determines whether the Model
active load. Refer to Figure

228

acts as a source or an

3-12

and/or the front panel

COMPLIANCE graph.
A. Press the AMPS/DWELL TIME key. This step displays

the present current value on the right display.

3-34

3.13.5 Example 5: Operation as Source and
Sink

To help illustrate the Model 228 source and sink
characteristics, this example shows how the Model 228 can
source a current to charge a capacitor and then when the
capacitor is fully charged, the Model 228 will be programmed
as an active load to accept the charge.

The voltage values of this example were chosen on the same
range (lOOV, lOOmA). The current values were chosen

the capacitor would charge and discharge at a somewhat slow
rate. In this way, the user could watch the display and see

what was going on in the circuit. The dwell time was chosen

so the Model 228 would remain at the memory locations long
enough to see the capacitor charge and discharge.

Even though modulation is a parameter of memory location,
it was not used in this example. Memory location 2 turned on
the sink mode. This is not required for less than 50W dissipa­tion. Also, note that while Program 2 is active, sourcing
capabilities is reduced.

1. Connect a

lO,OOO~F, 50V

capacitor on the output terminals
of the Model 228. Observe proper polarity when connec­ting the capacitor.

2, Charging the Capacitor (Operating as a Source). Program

memory location 1 for the following parameters:
A. 50V
B.

25d

C. 60 second Dwell Time
D. Turn off modulation.
E. Turn off sink mode.

3. Discharging the Capacitor (Operating as an Active Load).
Program memory location 2 for the following parameters:

A. 20V

B.

25d

C. 60 second Dwell Time
D. Turn off modulation.
E. Turn on sink mode.

4. Program the dwell time of memory location 3 to zero.

5. Set the Model 228 to the continuous program mode.

6.

Set the Model

228

to the operate mode.

7. Press the START/STOP key.

8. Watch the front panel displays.

SO

that

+I is on). The capacitor is charging at the rate programmed.
When the capacitor is charged to 5OV, the amps display
shows approximately zero current flowing (capacitor charg­ed). The LED to the right and left of the +V symbol are on
indicating that the capacitor is at the voltage level program­med.

When the Model 228 is in memory location 2, the capacitor is
discharging. Note the voltage on the left display. It decreases
as the capacitor discharges. As the capacitor discharges, the
compliance graph shows the Model

228

in current limit (LED
above the -1 is on). When the capacitor is discharged to the
20V programmed level, the LED to the right and left of the

+V symbol are on indicating that the capacitor is at the level

programmed.

This simple example illustrates several operating modes of the

Model 228. The following features and functions of the

Model 228 are used in this example.

1. Programming a voltage value.

2. Programming a current value.

3. Programming memory control mode (continuous).

4. Programming the five parameters of a memory location:
Voltage, Current, Dwell Time, Modulation, Source or
Sink.

5. Operation as a source (memory location 1).

6. Operation as an active load (memory location 2).

3.13.6 Example 6: Fabricating Output

Waveforms

The Model 228 is capable of fabricating output waveforms.

With the 100 available memory locations, the Model 228 can
fabricate waveforms with up to 100 individual steps.
steps of a waveform may not be necessary. A less com­plicated waveform could consist of just two memory loca­tions. A square wave is an example of a two memory location
waveform. The following is an example of programming the
Model 228 to output a squarewave of + 5V to OV at 20Hz. To
keep the example simple the current parameter for each of the

two memory locations will be set to 1OOd.

NOTE

To avoid confusion in this example, set all the
parameters of memory location 3 to zero.

100

When the Model 228 is in memory location 1, the capacitor is
charging. Note the voltage on the left display. It increases as

the charge on the capacitor charges. The compliance graph
shows the Model 228 is in current limit (LED just above the

1.

Turn on the Model 228 and allow ten minutes for warm
up.

2.

Press VOLTS/MEMORY STEP, SELECT. (Selects volts

display and sets the left display for modification).

3-35

3. Press 5, .,
voltage for 5V).

4. Press AMPS/DWELL TIME, SELECT. (Selects amps
display and sets the right display for modification).

5. Press .,
current for lOOmA).

6. Press AMPS/DWELL TIME, SELECT. (Selects dwell time
display and sets the display for modification).

7. Press ., 0,2,5, ENTER. (Programs memory location 1 for
25msec dwell time).

8. Press VOLTS/MEMORY STEP, SELECT. (Selects
memory step display and sets the display for modifica-

tion).

9. Press 2, ENTER. (Selects memory location 2).

10. Press VOLTS/MEMORY STEP, SELECT. (Selects volts
display and sets the display for modification).

11. PressO, .,
O.OV)

12. Press AMPS/DWELL TIME, SELECT. (Selects amps
display and sets the display for modification).

13. Press ., 1, 0, 0, ENTER. (Programs memory location 2
current for lOOmA).

14. Press AMPS/DWELL TIME, SELECT. (Selects the dwell

time display and sets the display for modification).

15. Press ., 0, 2, 5, ENTER. (Program memory location 2
dwell time to 25msec).

16. Connect load.

17. Press CONTINUOUS, OPERATE, START/STOP.

(Selects the continuous memory control mode, enables
the output and starts the continuous mode).

Upon completion of step 17, the Model 228 outputs a SV to

OV, 2OHz square wave. Refer to Figure 3-14.

-+5V-7

ov

0, 0, ENTER. (Programs memory location 1

1, 0, 0, ENTER. (Programs memory location 1

0, 0, ENTER. (Programs memory location 2 for

25msec

\

\

i, 1

J

\

3.13.7 Example 7: Using the External Trigger
(Input and Output)

A TTL level negative going pulse of greater than 1Opsec ap­plied at the rear panel external TRIGGER connector initiates

the selected memory control mode (Single Step, Single Cycle
or Continuous). The pulse starts the memory control mode in
the same manner as the front panel START/STOP key. To
output any programmed values, the memory control mode

must be selected, the OPERATE key enabled and the proper

external trigger pulse must be applied to the rear panel exter­nal TRIGGER input connector.

The external trigger output is a TTL level negative going
greater than 10psec pulse that signifies the completion of a
programmed dwell time. The pulse appears at the rear panel
external trigger output connector at the end of the progam­med dwell time in all three memory control modes (Single
Step, Single Cycle and Continuous). For the single cycle and
continuous memory control mode, there is an output pulse at
the end of every programmed dwell time. For the single step
mode, there is an output pulse at the end of the programmed
dwell time for the one memory location. To go on to the next
step, (memory location); and therefore output another pulse,
another external trigger input pulse is required. Refer to
paragraph 3.7 Memory Control Group.

As an example of using external input and output triggering,
assume the Model 228 is to be used in conjuction with the
Model 195A System DMM. The Model 228 can be program­med to output up to 100 voltage/current levels for given
periods of time. As each output voltage/current is applied,
the Model 228 triggers the Model 195A to take a reading.
When the Model 195A completes its reading, it triggers the
Model 228 to output the next programmed voltage/current
value. The sequence repeats itself until all readings have been
taken.

To use the Model 195A with the Model 228 perform the
following steps:

1. Connect the Model 228 and the Model 195A as shown in
Figure 3-15. Use suitable shielded cables with BNC connec-

tors. The Model 195A voltmeter complete output should
be connected to the Model 228 external trigger input. The
Model l95A external trigger input should be connected to

the Model 228 external trigger output.

3-36

Figure 3-14. Output Waveform

2. Place the Model 195A in the external trigger mode.

3. Connect both the Model 228 and the Model 195A to the
circuit under test.

4. Program the Model 228 with the desired output voltage,
current and dwell time values (refer to paragraph 3.10,
Examples 1, 2 and 3). Set the Model 195A to the ap-

propriate function and range. If desired, enable the Model
195A data buffer for reading storage.

5. Select the Model 228 memory control mode. To illustrate
this example, select the single step mode.

6. Place the Model 228 in the operate mode.

7. Press the START/STOP key on the Model 228 to output
the first voltage/current value.

8. Press the Model 195A front panel trigger button. This

starts the measurement cycle on the Model 195A.

9. After the Model 195A completes the reading, it triggers

the Model 228 into the next memory location; and
therefore, output the next voltage/current value.

10. Each instrument will trigger the other until the trigger cy­cle is stopped.

CAUTION

Do

not exceed 30V between the external

trigger connectors (outer ring) and chassis

ground or instrument damage may occur.

1 SOURCE 1

1OOV MAX

IF THE EXTERNAL VOLTAGE SOURCE IS NOT A MODEL 228, THE
DIODES SHOWN (DJ a D2) SHOULD BE USED TO PROTECT THE EX­TERNAL SOURCE FROM SUCH ERRORS AS:

1. INCORRECT MODEL 228 PROGRAMMED POLARITY.

2. IMPROPER POWER ON SEQUENCE.

3. EXCESSIVE MODEL 228 PROGRAMMED VOLTAGE.

I< leOlAMP 1OV MAX TO 1.01~ I< lO.lA

& GROUND

CASE

-

Figure 3-16. Connection for Floating Operation

MODEL 195

REAR PANEL

EXTERNAL

TRIGGER

I

Figure 3-15. External Trigger Connections

3.13.8 Example 8: Floating Operation

(Extended Compliance)

The Model 228 may be floated up to 1OlV off of chassis
ground (earth ground). Floating the Model 228 off of earth
ground increases the compliance voltage by that level. The
maximum float voltage is 101V and the maximum compliance
voltage is 1OOV. This increases the compliance level to 201V.
This does not mean that the Model 228 will deliver 2OlV of
compliance. 1OOV is from the Model 228 and 101V from the
external supply. A second Model 228 is a good choice to use
for the external supply. Before floating the Model 228 above
earth ground with an external supply, always check for the

proper circuit connections. Figure 3-16 shows the proper con-

nections when floating the Model 228 above earth ground.

CAUTION

When an external voltage source is con­nected in series with the Model 228 output

(as shown in Figure 3-161, care should be

taken to observe the power limits specified

in Figure 3-12. Also, the current MONITOR

and MODULATION connectors are held

within a few volts of the OUT - terminal by

the Model 228.

3.14 APPLICATIONS

The following applications allow the Model 228 to be used in
several situations including: source current and an active load
(current sink).

3.14.1 Low Resistance Measurements

Connectors, switch and relay contacts, printed circuit boards
and other devices with @ resistances can be measured with
current, source and sensitive voltmeters, For example: Using

1OA and ImV range gives 1OO~Q resolution (lmV/lOA) =
XX&Q . This resolution is obtainable without using an addi­tional digital multimeter.

3-37

µΩ

NOTE

For this example remote sensing should be used.

The four terminal measurement eliminates the effects of test
lead resistances. The Model 228 could be used to supply a
current (I) through the device under test (DUT). This devel­ops a voltage (IR

) which could be read by the sensitive

DUT

voltmeter. Using a 100mA current, the 10nV resolution of the
Keithley Model 181 Nanovoltmeter corresponds to 0.1
Thermal EMFs, electrochemical and other effects add an
extraneous DC voltage (V

) to the voltage developed by

OFFSET

the current source. This offset may be eliminated by applying
first a positive and then a negative current, both of the same
magnitude (I).

For positive current: V
For negative

current: V

+ = IR

X

- = -IR

X

DUT

DUT

+ V

+ V

OFFSET

OFFSET

The difference of these voltages is as follows:

(V

-V

X+

X-

)=(IR

DUT

+V

OFFSET

)-(-IR

DUT

+V

OFFSET

)=2IR

DUT

or

=

R

DUT

(V

X+

-V

)

X-

2I

The DUT can be installed in the Model 8003 Low Resistance
Test Box, which employs Kelvin sensing and includes all
interconnecting cables to Models 181 and 228.

The same measurement techniques can be applied to materi­als testing, where a metal under stress eventually microfrac­tures, causing an increase in resistance. Small laboratory
samples or even large airplane wings can be tested in this
manner. Refer to Figure 3-17 for an example configuration.

V

OFFSET

228

CURRENT

SOURCE

R

DUT

181

NANOVOLT

METER

Figure 3-17. Low Resistance Measurements

3.14.2 Battery Tests

The Model 228 is capable of acting as a source or as a accurate
and stable load. Testing the life of a battery requires such a
load. The Model 228 could be set to dissipate power from the
battery. The load conditions could be programmed over the
IEEE-488 bus or from the front panel.

Figure 3-18 shows the configuration of the Model 228 sinking

.

power from the battery. The battery in the figure is rated at
10V therefore the Model 228 should be programmed for a
voltage less than 10V in order to operate in the sink mode.
When the voltage of the Model 228 is less than the voltage of
the battery, current is drawn from the battery into the Model

228. The COMPLIANCE graph shows that the instrument is
operating in the sink mode. The voltage is positive but cur­rent is being drawn from the battery which shows up on the
COMPLIANCE graph as negative current.

CAUTION
NEVER change polarity on the Model 228A
to discharge an electrochemical cell.
Doing so will cause a large current surge
that will damage the power supply of the
Model 228A. ALWAYS allow the cell to dis­charge to 0V before changing polarity to
charge the cell in the opposite direction.
See paragraph 3.12.7 for details.

The battery could be discharged in this manner. A data log­ger would be useful to log the decline in battery voltage over
a long period of time. The Keithley Model 197 DMM has a
built-in 100 point data logger that would be ideal for this
application. The data logger of the Model 197 has six select­able rates at which the data may be logged automatically. It
also has a numerical trigger for manual data logging. The
automatic rates range from three readings per second to one
reading per hour. The Model 197 and the Model 228 would
work in conjunction with each other to accomplish the bat­tery test. Figure 3-19 shows the configuration of the Model
228, Model 197 and the battery for the test.

When using the Model 228 to test power supplies; most
power supplies would be damaged if external voltages or
currents are forced upon them. Figure 3-20 is a suggested
protection circuit. The two diodes in Figure 3-20 protect most
supplies in the event of the following errors.

3-38

1. Incorrect Model 228 polarity.

2. Improper power on sequence.

3. The Model 228 is programmed for excessive voltage.

3.14.3 External Modulation

The output of the Model 228 may be externally modulated.
This means the user supplies a low frequency (DC to 6OOHz)
low voltage (+ 1OV) signal that is superimposed on the output
signal of the Model 228. This external AC signal is applied to
the external modulation terminals on the quick disconnect
board and therefore the output signal, The polarity of the
modulation is determined by the programmed polarity of the

IJ BATTERY

-I

1

-

-

1ov

l-

output signal. The input resistance to the external modulate

terminal is 6.8kn. The maximum modulation with the output

programmed to zero is +O.OV to -1OV. The maximum

modulation with the output programmed to full scale is

+1ov to -o.ov.

Figure 3-18. Battery Life Test

HI

Z BATTERY

1

Figure 3-19. Data Logging Configuration

INPUT

I

MODEL 197 DMM

LO a

The front panel MODULATE I and MODULATE V LEDs in­dicate which function is selected.

The external modulation feature could be used to add low fre­quency signals to the Model 228 output. An example could be
performing power supply rejection tests without the burden
of large transformer or additional power amplifiers. Figure

3-21 shows the configuration for using the external modula­tion feature. Figure 3-22 shows a typical modulated output.

where:

PSRR = loglo -

+

Use shielded cables when externally modulating
the output of the Model 228. The shield should
be connected to output LO. Shield cables help in
reducing extraneous noise.

Vi

vo

NOTE

PROTECTION FOR USEkS SUPPLY

Figure 3-20. Power Supply Protection Circuit

3-39

QUICK

DISCONNECT

BOARD

MODEL 228

*EXTERNAL

MODULATION CONNECTkR- - -

L

EITHER VOLTAGE OR CURRENT

MAY BE MODULATED.

‘ROGRAMMED

LEVEL +

I- -o;T-+-‘l
I

OUTPUT

AC MODULATION SUPERIMPOSED

ON PROGRAMMED LEVEL

POWER

SUPPLY .

UNDER

TEST

AC DIGITAL

VOLTMETER (Vj)

I

OUT

I

OUT - ‘,

I

_ IN

I _

SHIELD

CAUTION

DO NOT EXCEED RATED SPECIFICATIONS FOR

MODULATION VOLTAGE OR MODULATION CURRENT.

INSTRUMENT DAMAGE MAY OCCUR.

CAUTION: MOD IS NOT ISOLATED FROM OUTPUT.

Figure 3-21. Connections for External Modulation

/ MODEL 228 OUTPUT;h

AC DIGITAL

VOLTMETER (Vo)

PSRR = 20 log10 3

vo

OV

Figure

I
I

T-

3-22. Typical Modulated Output

3.14.4 Ramp Generation

A very accurate ramp may be generated by charging a
capacitor with the Model 228. The Model 228 charges the
capacitor with a constant current up to the compliance limit
of the Model 228 or the working voltage of the capacitor.
Figure 3-23 shows the Model 228 connected to a capacitor.
Figure 3-24 shows the ramp that is generated by the constant
current being applied to the capacitor.

II

j 1 LOAD CAPACITOF

II

- vc
P.

Figure 3-23. Ramp Generation

3-40

228 has a built-in IEEE-488 interface that allows the test cir­cuit to be incorporated into the measurement system. Figure
3-27 shows the configuration with the Model 228s connected

to the computer over the bus.

With the system configuration, the computer may be pro-

grammed to control the testing automatically. The Model 228
responds to IEEE-488 protocol concerning commands and
data. With the Keithley Model 8573 IEEE-488 interface the
Model 228 may be controlled with the IBM PC or XT. The
Model 8573 IEEE-488 is supplied with its own software boot
disk and instruction manual. The instruction manual pro­vides clear instructions for operating the Model 8573 with the
IBM PC or XT.

Figure 3-24. Ramp Characteristics

The ramp is generated as the capacitor charges. When the
compliance limit of the Model 228 is reached or the capacitor
is fully charged, the ramp levels out to the voltage level on the
capacitor. The ramp could be used with a data logger (e.g.
Keithley Model 197 DMM in data logger mode). The data
logger could be used to store up to 100 data points of the

ramp to verify the accuracy of the ramp.

3.14.5 Power Semiconductor Testing

The Model
such as VMOS FETs, diodes, power Bipolar transistors, etc.
Typical curves for the transistors may be obtained using one
or two Model 228s. The Model 228 supplies up to 1OOW for

these applications. Obtaining the curves for bipolar tran­sistors involves two Model 228s. One Model 228 is connected
between the base and emitter and another Model 228 is con­nected between the collector and the emitter. Figure 3-25

shows the configuration for obtaining the family of curves for

a power transistor. The curves shown are the collector-

emitter voltage versus collector current (VCE, 1~ curves).

228

is suitable for testing power semiconductors

Other transistor tests may be performed using the Model 228
and the configuration shown in Figure 3-25. Examples of
these tests include:

1. DC Current Gain-The graph of DC current gain shows
collector current (1~) versus hfe.

2. “ON” Voltages-The graph of “ON” voltages shows the

collector current (1~) versus the “ON” voltage of the tran­sistor.

3. Collector Saturation Region-The collector saturation
region graph shows base current (1~) versus collector emit­ter voltage (V&.

MODEL 228 MODEL 228

I

I

Most VCE/IC curves illustrated in data manuals show the
maximum safe forward bias area. This area is self ex-

planatory and should not be exceeded. Figure 3-26 shows
typical a structure of VCE,IC curves. Also shown in Figure
3-26 is the maximum safe forward bias area.

For incoming inspection testing, manual testing may not be

cost efficient. The configuration shown in Figure 3-25 may be
connected to the IEEE-488 bus and a computer. The Model

Figure 3-25. Power Transistor Test Set Up

3-41

COLLECTOR

CURRENT

(ICI

MAXIMUM

SAFE FORWARD

bipolar transistor. Figure 3-28 shows the configuration using
a FET instead of a bipolar transistor. Figure 3-29 shows the
family of curves for a FET instead of a bipolar transistor.
Figure 3-30 shows the automated test set up with a FE?’ in­stead of a bipolar transistor.

f

F

Y

Figure 3-26. Power Transistor Ic/VcE

CONTROLLER IEEE-488 BUS

MODEL 228

IB BASE CURRENT

COLLECTOR-EMITTER VOLTAGE (VCE)

I

Curves

VDS

1

MODEL 228

c

Figure 3-26, FET Test Set Up

Using the bipolar capability of the Model 228,
both polarity transistors can be tested without
rewiring.

DRAIN

CURRENT

(ID)

MAXIMUM

SAFE FORWARD

BIAS AREA

L

NOTE

4

f

MODEL 228

1

/

/

id

Figure 3-27. Automated Test Set Up

The test set up is shown in Figure 3-25, the curves shown in
Figure 3-26 and the automated set up shown in Figure 3-27
could all apply to FETs as well as bipolar transistors. In Figure
3-25 the set up would be slightly different for a FET than for a

3-42

/

DRAIN-SOURCE VOLTAGE (VDS)

I

Figure 3-29. FET Curves

-T-

I-T-

Figure 330. Automated Test Set Up for FETs

3.14.6 Compensation for Noise

OUTPUT NOISE
For most applications, electrical noise coming from the

Model 228 is negligible. However, some Model 228 users

may have some output noise questions when operating this
instrument in extremely sensitive applications. The follow­ing information will help you determine possible sources
of the noise, which noise frequency range your test applica­tion is sensitive to, and what you can do to isolate or reduce
the noise.

To check the circuit’s noise sensitivity, try the following:
COMMON MODE-Connect a sine wave generator be-

tween the “earth” ground and circuit ground. Monitor any
changes in the circuit’s performance as frequency is swept
to determine its noise sensitivity.

NORMAL MODE-Connect a sine wave generator in series
with “safe” level (<3OV) signal lines. Be careful not to
violate grounding through the function generator (since
many function generators connect one output terminal to

“earth” ground). Isolate the function generator from high
level ( > 30V) signals with a transformer. Check circuit per­formance as in common mode testing to determine noise
sensitivity.

NOISE SOURCES
There are many possible sources of electrical noise both

from the Model 228 and from external sources. The follow­ing characterizes noise sources within the Model 228:

l

The Model 228’s microprocessor is isolated from the out-

put circuitry by opto-isolators. However, some
microprocessor hash in the 25400MI-I~ range may appear
on the output due to capacitive coupling within the
Model 228. When viewed with a wideband oscilloscope,
the noise may look much greater than low frequency
noise. However, this is usually not a problem in ex­periments since it is mostly common mode and not seen
across the load. The low common mode rejection ratio
of most scopes at these frequencies impairs their ability
to make accurate normal mode (across the load) noise
measurements.

l

There may be low level noise at the Model 228 power line
frequency.

l

There may also be some noise generated at 5OkHz and
harmonics of 5OkHz due to the switching power supply.

Before you can isolate or reduce electrical noise effects in
your application, you must determine what frequencies
your test is most sensitive to.

l

A good source of information is the specification sheet
from the device under test.

l

Add a “known” controlled noise source (such as a func-

tion generator) to the circuit and measure the circuit’s sen­sitivity to it.

l

Set up a “noise free” environment, then add one noise
source at a time to determine which noise sources affect
the test.

Some noise sources in typical laboratory environments
include:

l

Equipment with Microprocessors and/or Digital Circuitry:
This includes personal computers, peripherals, and test

equipment. Noise from these sources is coupled through
cables. Frequency components of this type of noise in­clude multiples and subharmonics of internal clocks and
hash from signal edges.

l

Computer Terminals: Terminals may generate noise at
l5kI-I~ and harmonics of l5kI-I~. In addition, some
lMHz400MHz microprocessor hash may be generated.

3-43

l

Fluorescent Lighting: Noise can be generated at the har­monics of the power line frequency.

l

DC motors: All frequencies can produce some amount
of noise (white noise source).

l

Broadcast Stations and Commercial Transmitters: Again,
a continuous spectrum of noise is generated, most usually
around lMHz and above 50MHz.

l

Bypass the power supply at the circuit under test. Use
polystyrene, mylar or ceramic capacitors.

l

Shield the circuit. (A ground plane connected at only one

point will do.)

l

All wires over 6” long (including power supply line)

should be shielded or of the “twisted-pair” type. Note--

large diameter wire is usually less inductive than small

diameter wire of the same length.
CHECKING FOR NOISE SOURCES
When characterizing electrical noise, a spectrum analyzer

or an oscilloscope would be very helpful.

A spectrum analyzer is very useful when used with an
antenna and “sniffer” probe. The analyzer provides relative
amplitude and frequency information. Multiply the relative
amplitude information with the circuit sensitivity at par­ticular frequencies to determine the most significant
problems.

If your oscilloscope has an adjustable bandwidth control,
it may be used like a spectrum analyzer. Unfortunately,
many oscilloscopes have a greater sensitivity-bandwidth
product than most circuits. Note that spikes have less
energy than a continuous waveform of the same peak
amplitude.

NOISE REDUCTION TECHNIQUES
The following suggestions are “rules of thumb” which may

solve many commonly encountered problems.

Low Frequency Noise Reduction Techniques (to 300Hz)

Remember--two pieces of equipment may not be at the

same “ground” potential even if they are plugged into the

same power outlet box.

High Frequency Noise Reduction Techniques (300kHz­2OMHz)

To reduce high frequency noise, try the following:

l

Put the circuit under test in a conductive box (for full
shielding effects).

l

Make sure the leads on bypass capacitors are VI” or less
in length. This requires bringing conductors to capacitors,
not vice versa.

l

Use mica, glass, low-loss ceramic or polystyrene
capacitors.

l

Bypass all wires going in to or out of the circuit under test.

-Ferrite beads are most useful when the DC and peak
AC current does not exceed about 1OmA.

-Wire wrapped around a 10Q or 1OOQ carbon composi­tion resistor and soldered to its leads makes a good low
Q inductor capable of handling higher currents.

-Capacitors that short noise to protective shields should
have leads as short as possible (VI”). Feedthrough type
capacitors are preferred.

Low frequency noise is often the result of less than optimal
shielding, grounding or circuit layout. Try these solutions:

l

Run power lines and grounds for control circuitry

separately from noise-selection circuitry.

l

If you must ground one of the Model 228’s leads, do it
at the circuit under test. Only one “earth” connection is
allowed for a system to avoid ground loops.

l

Employ the “remote sense” capability of the Model 228.

l

Use twisted-pair wire for the Model 228’s output and
sense leads.

Medium Frequency Noise Reduction Techniques (3OOHz-

3OOkHz)
Lead inductance and capacitor equivalent series resistance

become significant at medium frequencies. Try the

following:

3-44

. Use bulkhead connectors bolted to the shield for coaxial

cables if possible.

l

Line filters (electromagnetic interference suppressors) in
a metal case work well at higher frequencies if bolted to
the circuit shield. Be sure to use the proper current rating.

l

Use twisted-pair wire for proper supply and sense lines.
Noise coupled into the Model 228 through sense lines
will appear on the output and degrade specified perfor­mance.

l

Avoid using a large value capacitor in parallel with a small
value capacitor since this can form a parallel resonant cir­cuit? Otherwise, isolate the two capacitors with a dam­ping resistor (lOtI carbon composition is a good starting
value).

* Large value capacitors appear inductive at high frequen-

cies while the small value capacitor may still appear

capacitive. The parallel combination will then have a
higher impedance at some frequencies than either
capacitor by itself.

3.14.7 Voltage/Current Transients

Under certain circumstances, the Model 228 will output vol­tage or current transients approximately lmsec in duration.
It is important to be aware of these transients and be
familiar with techniques to avoid them in situations where

their presence is damaging, or at the very least, a nuisance.

The possibility of a transient occurring only exists when

the Model 228 switches from current control to voltage con­trol (voltage transient) or from voltage control to current
control (current transient). In addition to obvious control
changes caused by programmed voltage and current para­meters in memory steps, control changes may also occur
when going from standby to operate, changing polarity or
changing ranges.

When the Model 228 is in standby, it is actually pro­grammed to output 0.4% of the range it is on. For example,
on the lOOV, lA range (R8), the instrument will be set to

0.4V and 4mA. The following table lists the standby settings
for each range. The controlling function (voltage or current)
in standby is determined by the load connected to the out­put. The table below shows the controlling function on each
range for the various load conditions. For example, with
a 5OQ load resistor and the lOOV, 1V range (R8) selected,

standby would put the output in current control.

ranges. When changing polarity, the instrument first goes
into standby and then goes into the programmed settings.
Thus, two steps have to be considered to see if a control
change occurs when switching polarity.

Amplitude of the transient is determined by the pro­grammed parameters of the memory step that caused the
control change. If the control change is going from current
to voltage control, maximum possible peak of the the tran­sient is the programmed current times the load resistor
(Ohms law). If the control change is going from voltage to
current control, the transient wilI approach the value of the
programmed voltage setting.

Example-Assume a current to voltage control change will
generate a transient. The settings at the voltage control step
are 1OV and lA. The load is a resistor of 25Q.

Maximum Peak Transient = lA x 25Q = 25V

In this example, the transient will exceed the 1OV pro­grammed voltage level by up to l5V Note that if the voltage
control step is programmed for 25V (or more), the transient
will not occur. At 24V, the transient will be minimal (not
more than 1V higher than the programmed voltage).

Controlling Function in Standby

Controlling

Standby

Range
Rl; IV, lOOmA

R2; IV, IA
R3; IV, 1OA
R4; lOV, lOOti 4OmV, 400@
R5; lOV, 24
R6; lOV, 1OA
R7; lOOV, lOOmA 4OOmV 4OOfi
R8; lOOV, lA 4OOmV, 4mA > loon

Being aware of the controlling function (voltage or current)
in standby is important because the Model 228 internally
goes into standby when changing polarity or ranges. When
changing ranges, the instrument will first go into standby
on the range it :is presently at, then go into standby on the
next programmed range, and finally go to the programmed
settings of that range. Thus, three steps have to be con­sidered to see if control changes occur when changing

Settings

4mV, 4006 > 1os-l
4mV 4mA
4mV, 40mA >O.lQ <O.ltl

4OmV, 4rn4 >lOQ < 1oi-l
4OmV, 40mA >lMl

Function

Voltage

>1n

> 1OOQ < 1000

> 10Q

Current

< 10Q

<lQ

<lkQ
< 109

<loon

Controlling Transients

Not all control changes will generate a transient. With
voltage in control, a transient will not occur in the next
memory step if the voltage settings are the same. For ex-

ample, going from a voltage controlled step set for 1OV to
a current controlled step also set for 1OV will not result in
a transient. With current in control, a transient will not oc­cur in the next step if the current settings are the same.
For example, going from a current controlled step set for

0.5A to a voltage controlled step also set for 0.5A will not
result in a transient. Careful programming using these
techniques should prevent most transients from occurring.

When a transient-generating control change cannot be

avoided, an interim step can be added between the two
steps to eliminate or at least minimize the transient.

Interim Step Programming
The purpose of the interim step is to induce the control

change at settings that wilI generate a momentary transient
at a level that will equal or approximate the acual voltage
level of the preceding or following memory step.

3-45

Voltage-b-Current Control Change-In this situation, the

momentary transient will approximate the programmed

voltage setting of the current controlled step. The interim

step should be programmed to a voltage setting that is iden­tical to the voltage setting of the voltage control step or very

close to the actual output voltage of the current control step.
The interim step must control current and output the same
voltage as the current control step. Thus, the current set-

ting of the interim step must be identical to the current set-

ting of the current control step.

Example-Assumptions: 1OfI load; NW, 1OA range for all

steps; Model 228 programmed as follows:

The interim step (step 2) is programmed for a current set­ting identical to the current setting of step 3. The voltage
setting of step 2 is high enough to put the step in current
control, yet low enough to make the transient insignificant.
The 2.01V transient is very close to the desired 2V output
of step 3 (see the following waveform).

Standby:

Memory

Step 1: output)

Memory

Step 2:

This simple, single step test sequence is intended to out-

put 1V at step 1 and 2V at step 2. However, a transient of

up to 1OV will be seen on the leading edge of step 2 (see

the following waveform).

40mV 4Orn.A 1OQ (Voltage controlled)

1V

1OV 024 lOs2 (Current controlled;

lA 1Odt (Voltage controlled; 1V

2v output)

IOV

2v

1v

To effectively reduce the transient, the following interim

step can be added between the two steps.

Current-to-Voltage Control Change-In this situation, the
transient will approximate the product of the current set­ting of the voltage control step times the load resistance.
The interim step should therefore be programmed to a cur­rent setting that is identical to the current setting of the cur­rent control step, or to a setting whose value times the load
resistor will calculate very closely to the output voltage of
the voltage control step. The interim step must control
voltage and output the same voltage as the voltage control
step. Thus, the voltage setting of the interim step must be
identical to the voltage setting of the voltage control step.

Example-Assumptions: 0.5Q load; lOV, 1OA range for all
steps; Programmed as follows:

Standby: 40mV 40mA 0.5Q (Current controlled)
Memory 2v

Step 1: 1.5v output)
Memory 3v 1OA 0.5Q (Voltage controlled; 3V

Step 2: output)

This single step test sequence is intended to output 2V at
step 1 and 3V at step 2. However, a transient of up to 5V
will be seen at the leading edge of step 2 (see the follow­ing waveform).

3A 0.5Q (Current controlled;

Standby:
Memory

Step 1:
Memory

Step 2:
Memory

Step 3:

3-46

40mV 40mA 1OQ (Voltage controlled)

1V

2.01V 0.2A 100 (Current controlled;
1OV 024 1On (Current controlled;

lA 1OQ (Voltage controlled;

1v output)
2v output)
2v output)

5v

3v

1.5v

J-

To effectively reduce the transient, the following interim
step can be added between the two steps.

Use the following general rules to avoid, eliminate or
minimize transients:

Standby:
Memory

Step 1:
Memory

Step 2:

Memory 3v

Step 3:

The interim step (step 2) is programmed for a voltage set-

ting identical to the output voltage of step 3. The current
setting of step 2 is high enough to put the step in voltage
control, yet low enough to make the transient insignificant.
The 3.005V transient is very close to the desired 3V output
of step 3 (see the following waveform).

4OmV 4OmA 0.5Q (Current controlled)

2v 3A 0.50 (Current controlled;

1.5v output)

3V 6.OlA 0.5Q (Voltage controlled; 3V

output)

1OA 0.53 (Voltage controlled; 3V

output)

IL- .

1. Avoid range changes in a test sequence. Use a range that
will accomodate all step programming of the test

sequence.

2. When progr amming, be aware of control changes. When
in voltage control, programming the next step at the same
voltage setting will prevent a transient from occurring.
When in current control, programming the next step at

the same current setting will prevent a transient from
occurring.

3. Use interim programming between transient-generating

test sequence steps.

4. A possible external solution to a transient is to install a

zener diode across the load to clamp the voltage at an
appropriate level.

3-4713-48

SECTION 4

IEEE BUS OPERATION

4.1 INTRODUCTION

This section contains information necessary to operate the
Model 228 over the IEEE-488
ard IEEE interface that allows the user to give commands and
read data via an external device. Front panel Programs 2,4, 5
and 6 may be activated over the bus.

A typical set up for controlled operation is shown in Figure

4-l.

Generally, a system will contain one controller and a

number of other instruments to which the commands are

given. Device operation is categorized

controller, talker and listener. The controller does what its
name implies; it controls the instruments on the bus. The

talker sends data while a listener receives data. Depending on
the type of instrument, any particular device can be a talker

only, a listener only or both a talker and a listener.

Any given system can have only one active controller, but
any number of talkers or listeners may be present up to the
hardware limitations of the bus. Generally, the bus is limited

to 15 devices, but this number may be reduced if higher than
normal transfer rates are required or if longer than normal
cables are used.

bus. The Model

into three operators:

228 has a stand-

4.1.1 Software Considerations

The most sophisticated computer in the world would be
useless without the necessary software. This basic require­ment is also true of the IEEE-488 bus, which requires the use
of handler routines as described in this section.

Before a controller can be used with the IEEE-488 interface,
the user must make certain that the appropriate handler soft­ware is present within the controller. With the HP-85 com­puter, for example, the HP-85 interface card must be used
with an additional I/O ROM, which contains the necessary
handler software. As another example, the IBM PC (use the
Keithley Model 8573 IEEE-488 interface) also requires handler
software. This handler software is on the disk that is provided
with the Keithley Model 8573.

Other small computers that can be used as controllers have
limited IEEE capability. The PET/CBM computer, for exam­ple, is incapable of sending multiline commands from BASIC,
although these commands can be sent through machine
language routines. The capabilities of other small computers
depends on the particular interface being used. Often, little
software “tricks” are required to achieve the desired results.

Only one device on the bus may be a talker at any given time
while several devices can be commanded to listen. Before a
device can be commanded to talk or listen it must be ap­propriately addressed. Devices are selected by their primary
address. Usually, each device on the bus has its own primary
address so that each device may be addressed individually.
The primary address of the Model 228 is set at the factory to

11. The primary address may be changed by front panel Pro­gram 3. For more information concerning front panel pro­grams refer to paragraph 3-11.

Once a device is addressed to talk or listen, the appropriate
bus transactions take place. For example: if the Model 228 is
addressed to talk, it places its data string on the bus one byte
at a time. The controller reads the information and the ap­propriate software can be used to direct the information to
the desired location.

From the preceding discussion, the message is clear, make
sure the proper software is being used with the interface.
Often, the user may incorrectly suspect that a hardware prob­lem is causing fault when it was the software that was causing
the problem all along.

4.1.2 Interface BASIC Programming
Statements

Many of the programming instructions covered in this section

use examples written in Hewlett-Packard Model 85 BASIC
and Keithley Model 8573 interface statements. These com­puters and interfaces were chosen for these examples because
of their versatility in controlling the IEEE-488 bus. This sec­tion covers those HP-85 and Model 8573 statements that are
essential to Model 228 operation.

4-I

A complete list of HP-85 BASIC and Model 8573 interface
statements is shown in Table 4-1. HP-85 statements have
one or three digit argument that must be specified as part of
the statement. The first digit is the interface select code, which
is set to 7 at the factory. The last two digits of those
statements with a d-digit argument specify primary address.

Those statements with a d-digit argument listed in the table
show a primary address of 11 (the default primary address of
the Model 228). For a different address the last two digits need
to be changed to the required value. For example, to send a
GTL command to a device using a primary address of 11 the
following statement would be used:

LOCAL 711.

Some of the statements have two forms; the exact configura­tion depends on the command to be sent over the bus. For ex­ample, CLEAR 7 sends a DCL command, while CLEAR 711
sends the DC command to device with a primary address of

11.

figuration file called CONFIG.SYS must be present on the
DOS boot disk (see the Model 8573 Instruction Manual).

1. Boot up the system in the usual manner and enter BASICA.

2. Place the Model 8573 software disk into the default drive
and load the program called “DECL.BAS”. Modify the
program by changing the XXXXX values in lines 1 and 2 to

16000.

3. Add the following lines to the declaration file:
7 NA$=“GPIBO”:CALL IBFIND(NA!$,BRDO%)
8 NA$=“DEVO”:CALL IBFIND(NA$,M228%)
9 V% =ll:CALL IBPAD(M228%,V%)

4. Now save the modified declaration file for future use.
Remember that you must load and run this short program

before using the Model 8573 programming examples

throughout this section, Also, do not use the BASIC

CLEAR or NEW commands after running this program.

4.1.3 Interface Function Codes

The Model 8573 statements, which are also listed in Table
4-1, are different than the HP-85 statements. Each of these
statements use the IBM BASIC CALL statement, with a dif­ferent variable passed as shown in the table. The command
words, such as IBCLR (Interface Bus Clear) and IBSRE (Inter­face Bus Send Remote Enable), are BASIC variables. These
variables must be initialized at the start of each BASIC pro­gram. These keywords should not be used for any other pur­pose in your BASIC program.

Before using the Model 8573 examples, the software must be
configured with the following procedure. Note that the
binary handler file called GPIB.COM and the system con-

Table 4-l. HP-85 and IBM BASIC Statements

HP-85

Action

Transmit string to device 11. OUTPUT 711;AS CALL IBWRT(M228%,CMDS)
Obtain string from device 11.
Send GTL to device 11. CALL LOCAL 711 CALL IBLOC(M228%)
Send SIX to device 11. CLEAR 11
Send DCL to all devices. CLEAR 7

Send remote enable.
Serial poll device 11.
Send local lockout.

7

Send GTL to device 11.
Send IFC.

TRIGGER 711
ABORT10 7

Statement Model 8573 Statement

ENTER 71 l;A$

REMOTE 7
SPOLL(711) CALL IBRSP(M228%,SB%)
LOCAL LOCKOUT

The interface codes are part of the IEEE-488-1978
standards. These codes define an instrument’s ability to sup­port various functions and should not be confused with pro­gramming commands found elsewhere in this section.

Table 4-2 lists the codes for the Model 228. These codes are

also listed on the rear panel of the Model 228. The codes are

located near the IEEE connector. The numeric value following

each one or two letter codes defines the Model 228 capabilities
as follows:

SH (Source Handshake Function)-The ability for the Model

228 to initiate the transfer of message/data on the data bus is

CALL IBRD (M228%,CMDS)

CALL IBCLR(M228%)
CMDS= CHRS(&H14):CALL IBCMD

(BRDO%,CMD$)

V% = l:CALL IBSRE(BRDO%,V%)

CMDS = CHR$(&Hll ):CALL IBCMD

(BRDO%,CMDS)
CALL IBTRG(M228%)
CALL IBSIC(BRDO%)

4-2

provided by the SH function.
AH (Acceptor Handshake Function)-The ability for the

Model 228 to guarantee proper reception of message data on
the data bus is provided by the AH function.

T (Talker Function)-The ability for the Model 228 to send
device-dependent data over the bus (to other devices) is pro­vided by the T function. Model 228 talker capabilities exist
only after it has been addressed to talk.

L (Listener Function)-The ability for the Model 228 to
receive device-dependent data over the bus (from another
device) is provided by the L functions. Listener function
capabilities exist only after the Model 228 has been addressed
to listen.

SR (Service Request Function)-The ability for the Model 228
to request service from the controller is provided by the SR
function.

Table 4-2. Model 228 Interface Function Codes

Code Interface Function
SHl Source Handshake Capability

AH1 Acceptor Handshake Capability
T6

Talker (Basic Talker, Serial Poll, Unaddressed
To Talk On LAG)

L4

Listener (Basic Listener, Unaddressed To

Listen On TAG)
SRI Service Request Capability
RLI Remote/Local Capability
PPO No Parallel Poll Capability
DC1 Device Clear Capability
DTI Device Trigger Capability
co
El

TEO No Extended Talker Capabilities

LEO No Extended Listener Capabilities

No Controller Capability

Open Collector Bus Drivers

RL (Remote-Local Function)-The ability for the Model 228
to be placed in the remote or local mode is provided by the RL
function.

PP (Parallel Poll Function)-The Model 228 does not have
parallel polling capabilities.

DC (Device Clear Function)-The ability for the Model 228
to be cleared (initialized) is provided by the DC function.

DT (Device Trigger Function)-The ability for the Model 228
to have its basic operation is provided by the DT function.

C (Controller Function)-The Model 228 does not have con-

troller capabilities.

TE (Extended Talker Capabilities)-The Model 228 does not

have extended talker capabilities.

LE (Extended Listener Capabilities)-The Model 228 does not

have extended listener capabilities.

4.1.4 Model 228 Interface Commands

Interface commands controlling Model 228 operation are
listed in Table 4-3. Not included in the table are device-

dependent commands, which are covered in detail in

paragraph 4-5.

Table 4-3. IEEE Command Groups

HANDSHAKE COMMAND GROUP

DAC = DATA ACCEPTED
RFD = READY FOR DATA
DAV = DATA VALID

UNIVERSAL COMMAND GROUP

ATN = ATTENTION
DCL = DEVICE CLEAR
IFC = INTERFACE CLEAR
REN

= REMOTE ENABLE
SPD = SERIAL POLL DISABLE
SPE = SERIAL POLL ENABLE

ADDRESS COMMAND GROUP
LISTEN:

TALK:

ADDRESSED COMMAND GROUP

STATUS COMMAND GROUP

LAG = LISTEN ADDRESS GROUP
MLA = MY LISTEN ADDRESS
UNL = UNLISTEN

TAG

= TALK ADDRESS GROUP
MTA = MY TALK ADDRESS
UNT = UNTALK
OTA = OTHER TALK ADDRESS

ACG = ADDRESSED COMMAND GROUP
GET = GROUP EXECUTE TRIGGER
GTL = GO TO LOCAL
SDC = SELECTIVE DEVICE CLEAR

RQS = REQUEST SERVICE
SRC2 = SERIAL POLL REQUEST
STB = STATUS BYTE
EOI = END

4-3

4.2 IEEE-488 BUS LINES

As shown in Figure 4-1, the signal lines on the IEEE-488 bus
are divided into three groups; management, handshake and
data lines. The management and handshake lines ensure that

proper data transfer and bus operation take place while the

data lines handle bus information. Each of the bus lines are

low true with approximately zero volts as a logic 1.

ATN (Attention)-The state of the ATN line determines
whether information placed in the data bus by the controller
is to be considered data or a command.

REN (Remote Enable)-Setting the REN line low (true) sends
the REN command and sets up the instrument on the bus for
remote operation. If REN is followed by the primary address
of the Model 228, then it will be the only instrument to be
placed in the remote mode.

TO OTHER DEVICES

MANAGEMENT

LINES)

HP-85 Programming Example-The REN line is set low
(true) by the HP-85 when the following line is entered into the
HI’-85.

REMOTE 711 (END LINE)

When the END LINE key is pressed, the Model 228 is placed
in the remote mode and the front panel REMOTE LED turns

on.

Model 8573 Programming Example-The REN line is set
low (true) by the IBM PC through the Model 8573 interface
when the following is entered into the IBM PC.

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“X”:CALL IBWRT(M228%,CMD$) (return)

When the return key is pressed the second time, the Model
228 is placed in the remote mode and front panel REMOTE
LED turns on.

IFC (Interface Clear)-The IFC command is sent by the con­troller to set the Model 228 to the talk and listen idle states.

The instrument responds to the IFC command by turning off

the front panel TALK or LISTEN LEDs if the instrument was

previously in one of those modes. To send the IFC command,

the controller only has to set the IFC line true.

BUS MANAGEMENT

Figure 4-l. Bus Structure

4.2.1 Bus Management Lines

The bus management group consist of five signal lines that
send certain single line bus commands and ensure an orderly

transfer of data. The five signal lines are:

44

HP-85 Programming Example-Before demonstrating the

IFC command, turn on the front panel REMOTE and TALK
LEDs by entering the following statement into the I-P-85:

REMOTE 711 (END LINE)

ENTER 7ll;A!$ (END LINE)

The front panel TALK and REMOTE LEDs should now be

on. The IFC command may now be sent by entering the

following statements into the HP-85:

ABORT10 7 (END LINE)

CLEAR 7 (END LINE)

After the END LINE key is pressed the second time, the TALK
LED turns off, indicating the Model 228 is in the talk idle
state. Note that the remote mode is not cancelled.

have accepted the data. Each device releases the NDAC line
at its own rate, but the NDAC line will not go high until the
slowest device on the bus has accepted the data.

Model 8573 Programming Example

ing the IFC command, turn on the front panel

and TALK LEDs

by entering the following statements into

-Before demonstrat-

REMOTE

the IBM PC.

V%

-1:CALL IBSRE(BRDO%,V%) (return)

CMD$=CHR$(&HA):CALL IBCMD(BRDO%,CMD$)

(return)

The front panel TALK and REMOTE LEDs should now be

on. The IFC command may now be sent by entering the

following statement into the IBM PC:

CALL IBSIC(BRDO%) (return)

After the return key is pressed, the TALK LED turns off, in­dicating the Model 228 is in the talk idle state. Note that the
remote mode is not cancelled.

EOI (End Or Identify)-The EOI is used to identify the last
byte of multibyte transfer sequence.

SRQ (Service Request)-The SRQ line is set low (true) by a
device when it requires service. SRQ may be identified by

reading the status word.

4.2.2 Handshake Lines

The handshake group consists of three handshake lines which

operate in an interlocked sequence. The interlocked sequence

ensures reliable data transfer regardless of the transfer se­quence. The rate of transfer is usually determined by the
slowest device on the bus. The three handshake lines are:

1. DAV (Data Valid)

2. NRFD (Not Ready For Data)

3. NDAC (Not Data Accepted)

After the NDAC line goes high, the source sets the DAV line

high indicating that the data is no longer valid. At this point,

the NDAC line goes low. The NRFD line is released by each
device on the bus, but does not go high until the slowest
device on the bus has released the line. The bus is now set to
repeat the sequence with the next data byte.

The sequence just described is used to transfer both data and
multiline commands. The state of the ATN line determines
whether the data bus contains data or commands.

DAV’

NRFD

NDAC

VALID

I
I
I

I

I

DATA

TRANSFER

BEGIN END

TRANSFER

I
I

I
I

DATA

SOURCE

ACCEPTOR

I

ACCEPTOR

Figure 4-2. Handshake Sequence

4.2.3 Data Lines

The DAV line is controlled by the source. The NRFD and
NDAC lines are controlled by the accepting devices. The
complete sequence is shown in Figure 4-2. This sequence
handles information one byte at a time.

Once the data is on the bus, the source checks to see that
NRFD is high. At the same time NDAC should be low from
the previous transfer. Once the NRFD

and NDAC lines are

properly set, the source sets the DAV line low. The NRFD
line goes low; the NDAC line goes high once all the devices

The IEEE-488 bus uses eight data lines that transfer data one
byte at a time. DIOl through DIOS (Data Input/Output) are

the eight data lines used transmit both data and multiline
commands and are bidirectional. The data lines operate with
low true logic.

4.3 SYSTEM SET UP PROCEDURE

There are two primary set up steps that prepare the system
for operation. The two steps are as follows:

4-5

1. Bus Connections-The Model 228 is connected to the bus
via the rear panel connector. It is a standard IEEE bus con­nector. Maximum cable length for any device on the bus is
20 meters. The Keithley Models 7008-3 and 7008-6 are
ideal for connecting instruments to the bus. Figures 4-3 and
4-4 show the connector pin assignments and the IEEE bus
connector. The connector contact designations are listed in
Table 4-4.

CONTACT 12

/

CONTACT 1

/

4.4 BUS COMMANDS

The Model 228 may be given a number of special bus com­mands through the IEEE-488 interface. This section briefly
describes the purpose of the bus commands which are

grouped into the following three categories:

Uniline Commands-Sent by setting the associated bus line
low.

Multiline Commands-General commands that are sent with
the ATN line low.

Device-Dependent Commands-Special commands that de-

pend on device configuration; sent with ATN high.

CONTiCT 24

CONTACT 13

Figure 4-3. Contact Assignments

2. Primary Address Selection-The primary address of the
Model 228 must be set to the appropriate value when using

the Model 228 in the addressable mode. The primary ad­dress is selected by using front panel Program 3. For more
information concerning the front panel programs refer to
paragraph 3.11.

Table 4-4. IEEE Contact Designations

Contact
Number

1
:

4

5
6

7

:
10
11
12
13
14
15
16
17
18

:“o
21
22

2

IEEE-488
Designation

0101
Dl02
Dl03
D104
EOI (24)”
DAV

NRFD
NDAC
IFC
SRQ
ATN
SHIELD””
Dl05
Dl06
D107
D108
REN (24)”
Gnd, (6)”
Gnd, (7)”
Gnd, (8)”
Gnd, (9)”
Gnd, (IO)”
Gnd, (I 1)”
Gnd, LOGIC

Type

Data
Data
Data
Data
Management
Handshake
Handshake
Handshake
Management
Management
Management

Ground

Data
Data
Data

Data
Management
Ground
Ground
Ground
Ground
Ground
Ground
Ground

4-6

Figure 4-4. Typical Bus Connector

*Number in parentheses refer to signal ground return of

referenced contact number. EOI and REN signal lines
return on contact 24.

**The cable shield is normally connected to contact 12. This

shield should be connected to ground only at the controller
end to avoid ground loop problems.

4.4.1 Uniline Commands

As state previously, uniline commands are sent by setting the
associated bus line low (true). The five uniline (single line)
commands are:

ATN (Attention) – The ATN are sent when the information on
the data bus is an universal or addressed command. Univer­sal and addressed commands are described in paragraphs

4.4.2 and 4.4.3. When the ATN line is high, the byte on the
bus is considered to be data. The Model 228 responds to the
appropriate universal and addressed commands when the
ATN line is low and to the device-dependent commands
when the ATN line is high, assuming it is properly
addressed.

REN (Remote Enable) – The controller sends the command to
all devices on the bus when remote operation is desired. The
Model 228 responds by setting itself up for remote operation
as indicated by the front panel REMOTE LED.

EOI (End Or Identify) – EOI is sent during the last byte of a
multilane transfer by setting the EOI line low. In this way, the
last byte is identified allowing variable length data words to
be transmitted. The Model 228 implements this command
when in the appropriate bus response mode as stated in para­graph 4.5.5.

IFC (Interface Clear) – The IFC command sets the bus to a
known state by setting the IFC line low (true).

SRQ (Service Request) – The SRQ line is pulled low (true) by
an external device thereby informing the controller the
device requires service. The Model 228 implements this com­mand in the appropriate bus response mode as stated in
paragraph 4.5.5.

When the END LINE key is pressed after the CLEAR 7 state­ment, the Model 228 reverts to the power up default condi­tions which are listed in Table 4-5. This means that all the
parameters of memory location 1 were set to the default con­ditions listed in Table 4-5. All the parameters in each memory
location are battery backed up. Therefore, the programmed
parameters are unchanged.

Model 8573 Programming Example

controls, program a voltage of 5.00V, a current of 100.0mA
and a dwell time of 3.00 seconds into memory location one.
Now enter the following statement into the IBM PC:

CMD$=CHR$(&HA):CALL IBCMD(BRD0%,CMD$)

(return)

When the return key is pressed, the Model 228 reverts to the
power up default conditions listed in Table 4-5. All the
parameters in each memory location are battery backed up.
Therefore, the programmed parameters are unchanged.

SPE (Serial Poll Enable) – The serial poll enable sequence is
used to obtain the Model 228 status byte. Usually, the serial
polling sequence is used to determine which of several
devices has requested service over the SRQ line. The serial
polling sequence is conducted as follows:

1. The controller sets the ATN line true.

2. The SPE command is placed on the bus by the controller.

3. The Model 228 is addressed to talk.

4. The controller sets the ATN line false.

5. The instrument then places its status byte on the bus to
be read by the controller.

6. The controller then sets the ATN line low and places SPD
on the bus to end the serial polling sequence.

– Using front panel

4.4.2 Universal Commands

The universal commands are sent when the ATN line is low
(true). There are six universal commands and their effect on
Model 228 operation is described as follows:

DCL (Device Clear) – The DCL command is used to clear the
Model 228, thereby setting it to a known state. This buffer is
set to location one.

HP-85 Programming Example

program a voltage of 5.00V, current of 100.0mA and a dwell
time is 3.00 seconds into memory location 1. Now enter the
following statements into the HP-85:

REMOTE 711 (END LINE)

CLEAR 7 (END LINE)

– Using front panel controls,

HP-85 Programming Example

ment automatically performs the serial polling sequence. To
demonstrate serial polling, turn the instrument off then on
and then enter the following statements into the HP-85:

REMOTE 711 (END LINE)

S=SPOLL (711) (END LINE)

DISP S (END LINE)

When the END LINE key is pressed after the S=SPOLL state­ment, the controller performs the serial polling sequence.
When the END LINE key is pressed after the DISP S state­ment the status byte value is shown on the CRT. The status
byte has a value of zero (0) with this example because all the
bits are set to zero (0).

– The HP-85 SPOLL state-

4-7

Table 4-5. DCL and SDC Default Conditions

Mode Value Status

Display
Function
Data Format
EOI
SRQ
Program Mode
Range
External Modulation
Trigger
Terminator
Sink Mode
Memory Location
Voltage
Current
Dwell Time
Program 1
Program 2
Program 3
Program 4
Program 5
Program 6
Program 9

Model 8573 Programming Example

a serial poll when the following statements are entered. To
demonstrate serial polling, turn the instrument off then on
and then enter the following statements into the IBM PC.

V%=1:CALL IBSRE(BRD0%, V%) (return)

CALL IBSRP (M228%, SB%) (return)

PRINT SB% (return)

When the return key is pressed after the CALL IBSRP
(M228%, SB%) statement, the controller performs the serial
polling sequence. When the return key is pressed after the
PRINT statement the status byte value shown on the CRT.
The status byte has a value of zero (0) with this example
because all the bits are set to zero (0).

SPD (Serial Poll Disable) – The controller automatically sends
the SPD command on the bus to end the serial polling
sequence in SPE.

UNT (Untalk) – The controller sends the UNT command to
clear the bus of any talkers.

D0

F0

G0

K0

M0

P0

R0

A & C

T6

CR LF

S
B
V

I

W

Copy

Sink

IEEE

Mod V

Mod I

Test

Reset

Left display = Volts, Right display = Amps, Left display ready for edit.
Standby. Output set to +4 counts on present range. Refer to paragraph 2.3.
Prefix of buffer location contents.
Send EOI
SRQ Disabled
Single Step Mode
Autorange
Dependent on previously programmed values of present memory location.
Stop on X
Carriage Return Line Feed
Dependent on previously programmed values of present memory location.
Present memory location.
Dependent on previously programmed values of present memory location.
Dependent on previously programmed values of present memory location.
Dependent on previously programmed values of present memory location.
Disabled
Dependent on previously programmed values of present memory location.
Not affected
Dependent on previously programmed values of present memory location.
Dependent on previously programmed values of present memory location.
Disabled
Disabled

– The IBM PC conducts

4.4.3 Addressed Commands

Each of the addressed commands are sent to a specific device
on the bus. Each device is selected on the basis of its primary
address. The Model 228 responds to these commands only if
the primary address of the command is the same as the pri­mary address of the Model 228. All of the following com­mands are implemented by addressing the Model 228 to
listen.

SDC (Selective Device Clear) – The SDC command performs
the same function as the DCL command except that only the
addressed device responds. The instrument returns to the set
conditions listed in Table 4-5 when responding to an SDC
command. In addition, the buffer and the display pointers
are set to memory location 1.

HP-85 Programming Example

trols program a voltage of 7V, a current of 1.5A and a dwell
time of 250msec for memory location 1. Now enter the fol­lowing statements into the HP-85:

– Using the front panel con-

UNL (Unlisten) – The controller sends the UNL command to
clear the bus of any talkers.

4-8

REMOTE 7l.l (END LINE)

CLEAR 716 (END LINE)

Notice that when the END LINE key is pressed after the

CLEAR 7ll statement that the Model 228 did not respond to

the SDC because the command was sent with the wrong
primary address (16). Now enter the following statement into
the HP-85:

CLEAR 711 (END LINE)

Where Pl is the command to set the instrument into the con­tinuous mode and T2 is the command to set the instrument to
the start on GET mode. Now the instrument may be triggered
to start with the following statement:

TRIGGER 7l1 (END LINE)

After this statement is entered, the front panel START/STOP
LED turns on indicating the instrument has been triggered. To
stop the continuous mode, enter the following statements into
the HP-85.

When the END LINE key is pressed after the CLEAR 711

statement, notice that the instrument returns to the power up

default conditions listed in Table 4-5. Note that the program
memory is cleared of previously stored data.

Model 8573 Programming Example-Using front panel
controls program a voltage of TV, a current of 1.5A and a
dwell time of 250msec for memory location 1. Now enter the
following statements into the IBM PC:

CALL IBCLR(M2288) (return)

When the return key is pressed, notice that the instrument
returns to the power up default conditions listed in Table 4-5.
Note also that the program memory is cleared of previously
stored data.

GET (Group Execute Trigger)-The GET command is used to
trigger devices to perform a specific action that depends on
device configuration. Although GET is considered to be an
addressed command, many devices respond to GET without
being addressed. Using the GET command is only one of
several methods that can be used to start or stop the Model
228 program operation.

HP-85 Programming Example-To help illustrate this ex­ample, first set the Model 228 to a known state, such as the
default conditions. As in the previous example, to do this use
the SDC command as follows:

OUTPUT 7ll;“T3X” (END LINE)

TRIGGER nl (END LINE)

Where T3 is the command to set the instrument into the stop
on GET mode. When the END LINE key is pressed after the
OUTPUT 711;“T3X” statement, the continuous mode is stop­ped. When the END LINE key is pressed after the TRIGGER
7l.l statement the START/STOP LED turns off indicating the
instrument has received the trigger.

The Model 228 also responds to the GET command without
addressing. This command is sent with the following HP-85
statement:

TRIGGER 7

Model 8573 Programming Example-To help illustrate
this example, first enter the following statements into the IBM

PC.

V%=l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“T2P2X”:CALL IBWRT(M228%,CMD$) (return)

When the return key is pressed the first time the Model 228
reverts to the conditions listed in Table 4-5. When the return
key is pressed the second time the Model 228 is placed in the
start on get trigger mode and the continuous mode.

REMOTE 711 (END LINE)

CLEAR 711 (END LINE)

When the END LINE key is pressed after the CLEAR 7ll
statement, the Model 228 reverts to the default conditions
listed in Table 4-5. Now enter the following statement into
the HI-85 to place the instrument in the single cycle
memory control mode (Pl) and start on GET trigger mode.

OUTPUT 711;“PlT2x” (END LINE)

P2 is the command to set the instrument into the continuous
mode and T2 is the command to set the instrument into the

start on GET mode. Now the instrument may be triggered

with the following statement:

CALL IBTRG(M228 % 1 (return)

After this statement is entered, the front panel START/STOP
LED turns on indicating the instrument has been triggered. To
stop the continuous mode enter the following statement into

the IBM PC:

CMD$ = “T3X”:CALL IBWRT(M228 % , CMD$)

(return)

4-8

T3 is the command to set the instrument into the stop on GET
mode. The next line provides the trigger required to stop the
continuous mode. After the trigger has been received the
front panel START/STOP LED turns off.

CALL IBTRG(M228 % ) (return)

GTL (Go To Local)-The GTL command is used to remove
the instrument from the remote mode. The REN line MUST
BE SET HI (FALSE) in order for the GTL command to restore
operation of the locked out Model 228 front panel controls.

HP-85 Programming Example-To illustrate this example
the Model 228 must first be placed in the remote and lockout
modes. To place the instrument in these modes enter the
following statements into the HP-85:

REMOTE 711 (END LINE)

LOCAL LOCKOUT 7 (END LINE)

When the END LINE key is pressed after the LOCAL

LOCKOUT statement, the Model 228 is in the remote mode
(REMOTE LED on) and the front panel controls are locked
out (except ON/OFF and LOCAL). The GTL command se­quence is automatically sent by the HP-85 with the following
statement:

LOCAL 711 (END LINE)

Note that the REMOTE LED on the front panel control is
restored. Setting the REN line false with the LOCAL 7 state­ment also takes instrument out of the remote mode.

Model 8573 Programming Example-To illustrate this ex­ample the Model 228 must, first be placed in the remote and
local lockout modes. To place the instrument in these modes
enter the following statements into the IBM PC:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“X”:CALL IBWRT(M228%,CMD$) (return)

NOTE
The Model 228 may be placed in the local mode
by pressing the LOCAL button on the front
panel.

4.5 DEVICE-DEPENDENT COMMANDS

The device-dependent commands allow the user to send com­mands to the Model 228 that perform the same operations as
the front panel controls (except for POWER ON/OFF). There
are a number of commands that control parameters which are
not available from the front panel and they are listed in Table
4-6. Each command is entered as an ASCII character followed
by a specific parameter that is sent over the bus by the con­troller. The bus treats these commands as data in that the
ATN line is high (false) when the commands are transmitted.

Several commands may be grouped together. Before a com­mand or command string is executed, the ASCII character X
must be sent. Commands sent without an X (execute) are re­tained within the command buffer until the execute character
is received.

The condition of the status word with the Model 228 is af­fected by the device-dependent commands. The status word
may be obtained from the unit by using commands covered in
this section. Refer to paragraph 4.5.13 for status word infor­mation. Illegal commands do not change the mode of the
Model 228, but the status byte condition changes as described
in paragraph 4.5.5. Normal Model 228 commands are
covered in the following paragraphs. All the device­dependent commands for the Model 228 are listed in Table
4-6. Table 4-7 lists the device- dependent commands that are
not available to the front panel.

The Model 228 executes the programmed commands in the
order listed in Table 4-8. This means that if a statement is
entered into the HP-85 as follows:

OUTPUT 7ll;“PlW3.5D1X” (END LINE)

When the return key is pressed after the CALL IBLOC(BD %)

statement, the Model 228 is in the remote mode (REMOTE
LED on). The GTL command sequence is automatically sent
by the IBM PC with the following statement:

CALL IBLOC(M228 8 ) (return)

After return key is pressed, the RMT indicator turns off and
the instrument is returned to local operation.

4-10

The Model 228 executes the commands in the following order
according to Table 4-8.

1. Displays memory step (Dl).

2. Selects the single cycle mode (PI).

3. Programs the dwell time to 3.5 seconds (W3.5).

With the Model 8573, the instrument executes the commands
in the same order as did the HP-85.

There are two types of commands that make up the device­dependent commands listed in Table 4-8. They are as follows:

Independent Commands-Commands that do not interact

Table 4-6. Device-Dependent Commands

with each other.

Timer Commands-Commands that control the time and
date.

Mode
Display

Program

Prefix

SRQ

Trigger

ommand

DO

Dl
D2
D3
D4

PO
2

Lit
M2

M4

M8

TO
Tl
T2
T3
T4
T5

T6
T7

Notes
Left Display

VOLTS
MEM STEP
VOLTS
MEM STEP
Display Message Mode

Single Step Mode
Single Cycle Mode
Continuous Mode

Buffer location contents with prefix.
Buffer location contents without prefix.
Full buffer contents with prefix.
Full buffer contents without prefix.
Volts, amps readings with prefix.
Volts, amps readings without prefix.

Disabled
Error (IDDC, IDDCO or No Remote)
Ready
End of Buffer
End of Dwell Time

Start on TALK
Stop on TALK
Start on GET

Stop on GET
Start on X
Stop on X

Start on External Trigger
Stop on External Trigger

Right Display
AMPS
AMPS

DWELL TIME

DWELL TIME

Terminator

inputs

Function

Y(ASCII)

Ym

Y mn

Y(DEL)

v

A

B
Fo
Fl

Any ASCII except capitals, numbers, + - / . or e

One Terminator

Two Terminator

None
Voltage

Current
Dwell Time
Memory Location

Standby (output set to +4 counts on present range). Refer to
paragraph 2.3 for details concerning the standby mode.
Operate (output is present on terminals).

4-11

Table 4-6. Device-Dependent Commands (Cont.1

Mode

Range

External Mod

Sink

status

Self Test

Command Notes

RO
Rl
R2
R3
R4
R5

R6
R7
R8

A0
Al

Autorange
lV, 100mA
IV, IA
lV, 10A
lOV, lOOmA
lOV, 1A
lOV, 1OA
lOOV, 100mA
lOOV, 1A

Turn off Voltage Modulation
Turn on Voltage Modulation

Turn off Current Modulation

EY
so

Sl
uo

Ul

JO

Turn on Current Modulation
Turn off sink mode.

Turn on sink mode.
Send Status Word

Send Error Status word
hadive 0; in statys byte.

Passed 2; in status byte.

Failed 1; in states byte.

EOI

Execute

KO

Kl

E

X

Send EOI, hold off bus until commands processed on X.

Send no EOI, hold off bus until commands processed on X.
Send EOI, do not hold off on X.
Send no EOI, do not hold off on X.

Execute other device-dependent commands.

I

4-12

Table 4-7. Device-Dependent Commands Not Available to the Front Panel

Mode
Display

Prefix

EOI

SRQ

Trigger

Command

04

KO
z

K3

MO
Ml
M2
M4
M8

TO
Tl
T2
T3
T4
T5
T6

-I7

Notes
Display Message Mode

Buffer location contents with prefix.
Buffer location contents without prefix.
Full buffer contents with prefix.
Full buffer contents without prefix.
Volts, amps readings with prefix.
Volts, amps readings without prefix.

Send EOI, hold off bus until commands processed on X.
Send no EOI, hold off bus until commands processed on X.
Send EOI, do not hold off on X.
Send no EOI, do not hold off on X.

Disabled
Error (IDDC, IDDCO or No Remote)
Ready
End of Buffer
End of Dwell Time

Start on TALK
Stop on TALK
Start on GET
Stop on GET
Start on X
Stop on X
Start on External Trigger
Stop in External Trigger

Terminator

Status

Execute
Range

Y(ASCII)

Yn

Ymn

Y(DEL)

uo
Ul

X
RO
::

R3
R4
R5
R6
R7
R8

Any ASCII except capitals, numbers, + - / . or e
One terminator
Two terminator
None

Send status word
Send error word

Execute other device-dependent commands.
Autorange

lV, 100mA
lV, IA
w, 1ov
lOV, 100mA
lOV, 1A
IOV, 10A
lOOV, 100mA
lOOV, 1A

4-13

Table 4-8. Hierarchy of Command Execution

Mode Command

*Display DO, Dl, D2, D3 and D4
*Function FO and Fl

*Prefix GO, Gl, G2, G3, G4 and G5
*EOI
“SRQ MO, Ml, M2, M4 and M8

*Program PO, PI and P2

*External Modulation
‘Trigger TO, Tl, T2, T3, T4, T5, T8 and 17
*Terminator Y(ASCII), Y(m), Y(mn) and Y(DEL1
*Status
*Execute X
*Self Test JO

**Range RO, Rl, R2, R3, R4, R5, R6, R7 and R8

***Inputs V, I, W and B

*Executed first

**Executed second

***Executed last

KO ,Kl, K2 and K3

AO, Al, CO and Cl

UO and Ul

4.5.1 Display Mode (D)

The following five commands set the display for the volts,
memory step, amps, dwell time or display message mode.

DO=T’he DO command sets the Model 228 for the volts
display and amps display mode. Volts is shown on the left
display. Amps is shown on the right display. Refer to

paragraph 3.7.

Dl=The D1 command sets the Model 228 for the memory
step and amps mode. The memory step is shown on the left
display. Amps is shown on the right display. Refer to
paragraph 3.7.

D2 = The D2 command sets the Model 228 for the dwell time
and volts display mode. Dwell time is shown on the right
display. Volts is shown on the left display. Refer to paragraph

3.7.
D3 = The D3 command sets the Model 228 for the dwell time

display mode. The dwell time is shown on the right display.
Refer to paragraph 3.7.

D4=The D4 command sets the Model 228 for the display
message mode. The display message mode allows the user to
display a customized message on the Model 228 front panel
display.

HP-85 Programming Example-To display and transmit
the present memory location with a prefix and display the
data on the HP-85 CRT, enter the following statement into
the I-P-85:

PROGRAM

5 DIM A$[501

10 REMOTE 711

(END LINE)
20 CLEAR 7 (END LINE) Clear the Model 228.
30 OUTPUT 711;“GODlX” Display present memory loca-

(END LINE)

40 ENTER 7ll;A$

(END LINE)
50 DISP A$

60 END

After typing in the program, press the RUN key on the HP-85

to run the program. After the RUN key is pressed the present

memory location with the prefix is displayed on the HP-85

CRT as follows:

NDCV+l.OOOE-2, ODCI+O.OOOE+O, W+3.500E+O,

COMMENTS
Dimension A$.

Set the Model 228 to the
remote mode.

tion on the Model 228 display
and send memory location
with Drefix.
Obtain data string.

Display data string.

B+l.OOOE+O

4-14

where:
DCV = O.OlV
Amps = .OOOOA
Memory Step = 1
Dwell Time = 3.5 seconds

N = function in control
0 = function not in control

This program can be used for any of the prefix (G) com­mands .

Model 8573 Programming Example-To display and

transmit the present memory location with a prefix and
display the data on the IBM PC CRT, enter the following
statements into the IBM PC.

V% -1:CALL IBSRE(BRDO%,V%) (return)

CMD$=“GODlX”:CALL IBWRT(M228%,CMD$) (return)

RD$ = SPACE$(W):CALL IBRD(M228 % ,RD$) (return)

PRINT RD$ (return)

12 3 4 12345

Notes

1. The first character on both displays must be a plus (+ ),
minus (-1, decimal point or the number 1. Otherwise it
will be ignored.

2. Characters 2, 3 and 4 on the left display and 2, 3, 4 and 5
on the right display will accept any displayable ASCII
character. Any character not displayed will appear as a “d”
segment. A “d” segment is shown as follows:

f3

d segment
1

3. The maximum number of characters for the displays that
can be sent is nine. The first four characters are shown on
the left display. The last five characters are shown on the
right display.

4. Depending on the program more than one message may be
displayed.

After the second statement, the Model 228 displays the pre­sent memory location on its front panel display and transmits
the data string to the computer. After the fourth statement,
the present memory location with the prefix is displayed on
the computer CRT.

As another example we will illustrate the

D4

(display
message) mode. Read the following paragraphs and do the
programming example.

The ASCII message is, of course, limited to the display of the
seven segment LEDs on the front panels of the Model 228.
Both front panel displays may be used to display the message.

The message may be controlled with the following com­mands:

D4aaaaaaaX=The command is D4 while the letter “a”
represents an ASCII character (up to seven characters may be
sent).

DO, Dl, D2 or D3=Takes the Model 228 out of the message
display mode (D4) and into the display mode that is program­med.

NOTE
For the following notes, refer to the display
numbering sequence shown.

HP-85 Programming Example-To display the message
“For self test send JO,” enter the following program into the
HP-85:

PROGRAM

10 REMOTE 711
20 OUTPUT 7ll;“D4 FORSELFX”
30 WAIT1000
40 OUTPUT nl; “D4 TEST X”

50

WAIT1000

60

OUTPUT 7l.l; “D4 SENDX”

70

WAITlOo

80

OUTPUT

90

WAIT5000

100 GOT0

110

END

7ll; "D4

20

JOX”

COMMENTS
Set for remote.

Display FORSELF.
Wait on second.
Display TEST.
Wait one second.
Display SEND.
Wait one second.
Display JO.
Wait 5 seconds.
Repeat.

NOTE
Make sure there is a space in the program be­tween D4 and the message. Otherwise an erratic
display will result.

When RUN key on the HP-85 is pressed the Model 228 dis­plays the following message:

Display operation may be restored by entering the following
statement into the HP-85:

OUTPUT T11;“DOX” (END LINE)

4-15

Model 8573 Programming Example-To display the mes-

sage “HELLO,” enter the following program into the IBM PC:

PROGRAM COMMENTS

10 V% =l:CALL IBSRE

(BRDO%,V%)

20 CMDS = ‘D4 HELLo”:CALL DisoIav HELLO.

After the return key is pressed the second time the Model 228
displays HELLO. Display operation may be restored by
entering the following statement into the IBM PC.

CMD$=“DOX”:CALL IBWRT(M228% ,CMD!§)

Set up for remote
operation.

4.5.2 Memory Control Mode (PI

The following three commands set the Model 228 to single
step cycle or continuous memory control mode.

PO=The PO command sets the Model 228 to the single step
memory control mode. The single step memory control mode
allows the user to step through the programmed memory lo­cations one at a time upon sending the PO command. One lo­cation per P2 command.

Pl=The Pl command sets the Model 228 to the single cycle
memory control mode. The single cycle mode allows one
complete cycle through the programmed channels.

P2=The P2 command sets the Model 228 to the continuous
memory control mode. The continuous mode allows a con­tinuous cycle through the programmed memory location.

HP-55 Programming Example-The following example il­lustrates the Pl (single cycle) memory control mode.

PROGRAM

10

DIM A!§ bO1

20

REMOTE 711

30

OUTPUT 7ll;“BlX”

(END LINE)

40

OUTPUT 711;“V511W1X” Set SV, 1A and 1 second

(END LINE)

50

OUTPUT nl;“B2X”
(END LINE)

60

OUTPUT 711;“V1OIW2X” Set lOV, 1A and 2
(END LINE)

70

OUTPUT 711;“B3X”
(END LINE)

80

OUTPUT 711;“V25IlW3X” Set 25V, 1A and 3
(END LINE)

90

OUTPUT 711;“PlX’
(END LINE)

100

OUTPUT 711;“DOGOX”
(END LINE) buffer location with

OUTPUT 7ll;‘TOx”

110

(END LINE)

120

ENTER 7ll;A$ (END LINE) Obtain start on talk.

130

DISP A$

140

END

After entering the program, press the HP-85 RUN key to run

the program. After the RUN key is pressed, the Model 228
steps through memory locations 1,2 and 3. The Model 228 al­so displays the programmed voltage for each of the memory

locations. Since the program specifies the single cycle mode,

the memory locations are stepped through only once. To do
so continuously, program P2 in line 90 instead of PI. The
HP-85 screen displays the full buffer contents for memory lo-

cation 3. This is because the TALK statement (Line 120) tells
the instrument to send its data string. Since the Model 228 is
presently on memory location 3, that data is sent over the
bus.

COMMENTS

Set up for remote opera­tion.
Set memory location

001.
dwell time in memory

location 001.
Set memory location

002.
second dwell time in

memory location 002.
Set memory location

003.
second dwell time in

memory location 003.
Set single cycle mode.

Set for volts display and
prefix sent.

Set for start on talk.

Display data string.

4-18

Memory f-

Modulation on or off, Sink on or off.
Memory ocation 2 =

ModuIatio
Memory Location 3

~.OOOE+O,W+~.OOOE+O,B+~.OOOE+O.

ocation 1 = Voltage, Current, Dwell Time,

on or off, Sink on or off.

“.

Voltage, Current, Dwell Time,

= b.JDcv + 2.5OOE + 1, ODCI +

To run the program press the F2 function key. After placing

the instrument in remote (line 40), the program sets memory
locations 1,2 and 3 for various parameters. Lines 110 and 120
set the instrument for buffer location output, single cycle
mode, start on talk trigger mode and volts display mode.
Lines 130 and 140 obtain the data string and displays it on the
IBM CRT. Lines 150 and 160 close the board and instrument
file.

Model 8573 Programming Example-The following pro-

gram illustrates the single cycle memory control mode (Pl)

over the bus using the IBM PC and the Model 8573 IEEE-488
interface. Load the modified DECL.BAS file into the IBM
computer (see Model 8573 Instruction Manual) and add the
following lines.

PROGRAM

10 NA$= “GPIBO” :CALL IBFIND

(NA!$, BRDO%)

NA$ = “DEVO” :CALL IBFIND

20

(NA!J,M228%)

30 V% =ll:CALL IBPAD

(M228%,V%)

40 V% -1:CALL IBSRE

(BRDO%,V%)r

50 CMDS=“BlX”:CALL IBWRT

(M228%,CMD!$)

60 CMD$=“V511W1X”:CALL

IBWRT(M228 % , CMD$)

70 CMD$=“B2X”:CALL IBWRT

(M228%,CMD$)

80 CMD$=‘VSIlW2X”:CALL

642280/a, CMD!§)

90 CMDfi=“B3X”:CALL IBWRT

(M228%,CMD$)

100 CMD!$=“V25IlW3X”:CALL

(M228%,CMD!§)

110 CMD$=“POGOX”:CALL IBWRT

(M228%,CMD$)

,J.20 CMD$=“TODOX”:CALL IBWRT

(M228%,CMD$)

130 RD!§= SPACE(6O):CALL IBRD

w28%,RD$)

140 PRINT RD$

150 V% =O:CALL IBONL

(BRDO%,V%)

160 CALL IBONL(M228%,V%)

COMMENTS

Find the board des­criptor.
Find the instrument
descriptor.
Set primary address
ro 11
Set remote enable.

Select memory
location 1.
Set SV, 1A and 1
second dwell time.
Select memory
location 2
Set lOV, 1A and 2

second dwell time.

Select memory
location 3
Set 25V, 1A and 3
second dwell time.
Selects buffer loca­output and single
cycle mode.
Select start on talk
and volts display
mode.
Obtain data string.

Display data string.
Close the board
file.

Close the instru­ment file.

4.5.3 Prefix IGI

When addressed to talk, the instrument will send a data string
containing information about the programmed current,

voltage, dwell time and memory location. This data string

can be sent with or without a p&ii. The prefix (G) com-

mands and their format are described as follows:
GO=Present Buffer Location Output. Sending the GO com-

mand allows the data to be sent with a prefix as follows:
NDCVfn.nnnE+n, I-Ln.nnnE+n, W+n.nnnE+n,

B+n.nnnEfn
Voltage, Current, Dwell Time, Memory Location

Gl=Present Buffer Location Output. Sending the Gl com-

mand allows the data to be sent without a prefix as follows:

+n.nnnEfn, fn.nnnE&n, +n.nnnE+n, +n.nnnEfn

G2 = Full Buffer Output. Sending the G2 command allows all
of the data in all 100 buffer locations to be sent with a prefix.
The format is as follows:

NDCV+n.nnnEfn, I+n.nnnEfn, Wfn.nnnEfn,
B+l.OOOE+2

. . . . . . . .

NDCVfn.nnnE+n, I+n.nnnE+n, Wfn.nnnE-t-n,
B+l.OOE+2

G3=Full Buffer Output. Sending the G3 command allows all
of the data in all 100 buffer locations to be sent without a
prefix. The format is as follows:

*n.nnnEfn, fn.nnnE+n, &n.nnnE+n, fn.nnnE+n

. . . . . . .

fn.n&~+~, &&nnEz!zn, -tn.nnnE_+n, +l.OOE+2

4-17

G4 =Present Voltage and Current Buffer Output, Sending the
G4 command allows the voltage and current data that is pres­ent on the output to be sent with a prefix. The format is as
follows:

prefix is desired in the data string, change line 60 to read as
follows:

60 OlJTPUT 7ll;“GlDOX”

NDCV+n.nnnE+n, I+n.nnnEfn, Wfn.nnnEfn,

B+n.nnnEfn
GS = Present Voltage and Current Buffer Output. Sending the

G5 command allows the voltage and current that is present
on the output to be sent without a prefix. Also, present out­put mode values are sent (operate or standby). The format is
as follows:

fn.nnnE&n, +n.nnnEfn, +n.nnnEfn, +n.nnnEfn

HP-85 Programming Example-The following program
sends the data string over the IEEE bus. In order to obtain the
data string from the instrument, the controller must perform

the following sequence:

1. Set ATN true.

2. Address the Model 228 to talk.

3. Set ATN false.

4. Input the data string one byte at a time.

NOTE
Press the END LINE key after each line is
entered.

PROGRAM

10 DIM A!$ [lO0]

COMMENTS

Dimensions A!$ for 100
characters.

20 REMOTE 711

Set instrument up for
remote operation.

30 CLEAR 7
40 OUTPUT nl;“BlX”

Clear the instrument.
Selects memory location

1.

50 OUTPUT 7ll;‘V1oI1w1ox”

Set lOV, 1A and 10
second dwell time.

60 OUTPUT 7U;“GODOX”

Programs the volts
display mode and the
Buffer location with

prefix mode.
70 ENTER nl; A$
80 DISP A!§

Obtain data string.

Display data string.
90 END

Once the program is entered, press the HP-85 RUN key to
start the program. The data string appears on the HP-85
CRT. The Model 228 is programmed for lOV, 1A 10 second
dwell time the prefix mode and the volts display mode. If no

The Gl command programs the instrument to drop the prefix
from the data string.

Model 8573 Programming Example-The following pro­gram sends the data string over the IEEE bus. In order to ob­tain the data string from the instrument, the controller must
perform the following sequence.

1. Set ATN true.

2. Address the Model 228 to talk.

3. Set ATN false.

4. Input the data string one byte at a time.

NOTE
Load the modified DECL.BAS file into the IBM
computer (see the Model 8573 Instruction
Manual) and add the following lines. Press the
return key after each line is entered.

PROGRAM

NAS = “GPIBO”: CALL IBFIND

10

(NAS,BRDO%)
NA$= “DEVO” :CALL IBFIND

20

(NA!$,IvI228%)
V % = 11:CALL IBPAD

30

(M228%,V%)
V% =l:CALL IBSRE

40

(BRDO%,V%)

CMD$ = “BlX”: CALL IBWRT

50

(M228%,CMD$)
CMD$=“VlOIlWlOX”:CALL

60

IBWRT(h4228% ,CMD$)

COMMENTS

Find the board de­scriptor.
Find the instru-

ment descriptor.
Set primary ad­dress to 11.
Send remote
enable
Select memory lo­cation 1.
Set lOV, 1A and
10 second dwell
time.

CMD$ = “GODOX” :CALL IBWRT

70

M228%,CMD$)

Set volts display
mode and buffer

output with prefix

mode.

RD$=SPACES(SO):CALL

80

Obtain data string.
(M228 % ,CMD$)
PRINT RD$

90

Display data

string.

V% =O:CALL IBONL

100

Close board file.

(BRDO%,V%)

CALL IBONL(M228 % ,V% )

110

Close instrument
file.

4-18

Once the program is entered, press the F2 function key to run
the program. The Model 228 is programmed for
second dwell time volts display mode and the buffer location
output with prefix mode. If the prefix is not desired, change
line 70 to:

70 CMD$=“GlDOX”:CALL

IBWRT(M228%,CMD$)

The G1 command programs the instrument to drop the prefix
from the data string.

lOV,

lA, 10

4.5.4 SRQ Response Mode (M)

The bus response mode determines whether or not the Model
228 requests service from the controller through the SRQ line,

Table 4-9 lists the conditions that cause an SRQ. Note that
the instrument can be programmed for one or more condi­tions simultaneously.

SRQ may be programmed by sending the
followed by a decimal number to set the appropriate bits in
the mask. Note that the instrument may be programmed for
more than one set of conditions simultaneously. To do so,
simply add up the decimal bit values for the required SRQ
conditions. For example, to enable SRQ under illegal device­dependent command option, send

send MOX. This command clears all bits in the SRQ mask.

END OF DWELL TIME -i

END OF BUFFER

ASCII

MlX. To

letter “M”

disable SRQ,

L

ERROR

READY

Table 4-9. SRQ Mask Commands

IDDC,

SRQ

c

iommand

i!
EZ

M4
M5

E
M8

IO
Ml1
Ml2
Ml3
Ml4
Ml5

*MO Disables SRQ.

SRQ Mask-The Model 228 uses an internal mask to deter­mine which conditions cause an SRQ to be generated. Figure
4-S shows the general format of this mask, which is made up
of eight bits.

End of

Iwell Time

Ind of
3uffer Ieady

IDDCO

Jo

Remote

X
X

X
X
X
X
X
X

Figure 4-5. Format of SRQ Mask

Figure 4-6 shows the format of the SRQ mask byte. Bits
within the mask can be controlled by sending the ASCII
character “M” followed by a decimal number from 0 to 15.

1 -SRQBY228--J

1 = ERROR

L I= END OF BUFFER

1 = END OF DWELL TIME

Figure 4-6. Format of SRQ Status Byte

Status Byte Format-The status byte format byte contains in­formation relating to data and error conditions within the in­strument. The general format of the status byte (which is ob-

tained by the serial poll@ sequence)
4-6. Note that

SRQ

mask.

Bit 6 provides a means to determine if an SRQ was asserted
by the Model 228. If this bit is set, service was requested by

the various bits correspond to the bits in the

the instrument. Bit 5 flags a Model 228 error condition. If
this

bit was set, an illegal device-dependent command

is shown in Figure

4-19

(IDDC) or illegal device-dependent
DCO) was set, or the instrument was not in remote when

programmed.

Bit 4 is set when the Model 228 is ready for operation. Bit 3 is
set when the end of the present programmed dwell time is
reached during program execution. Bit 2 is set if the end of
the buffer (program memory) is encountered when nm­ning a program.

Note that the status byte should be read to clear the SRQ line
once the instrument has generated an SRQ. All bits in the

status byte are latched when the SRQ is generated. Bits are

cleared when the status byte is read. Even with SRQ disabled,

the status byte can be read to determine appropriate instru-

ment conditions. In this case, bits 2, 3, 4 and 5 are con-

tinuously updated to reflect current instrument status;
however, bit 5 (the error bit) latches and remains latched until
the status byte is read, even if no SRQ occurs.

HP-55 Programming Example-Enter the following pro­gram into the l-P-85:

NOTE

After each line is entered press the END LINE

key.

PROGRAM

REMOTE 711

10

OUTPUT 711;“MlX”

20

command

COMMENTS

option (ID-

Set up for remote

operation.

I$ogram for SRQ on

error

OUTPUT 711;“RgX”

30
40

s = SPOLL(711)

DISP”B7 B6 B5 B4 B3 B2

50

Attempt to program

illegal option.

CoEduci serial poll.

Identify the bits.

Bl BO”
FOR I=7 TO 0 STEP -1

60

DISP

70

BIT (S,I);

Loop eight times.

Display each bit

position.

NEXT I

80

DISP

90

END

100

After the program is entered, press the HP-85 RUN key to run

the program. The computer places the instrument in remote
and then programs the SRQ mode of the instrument. Line 30
attempts to program an illegal option (R9), at which point the
instrument generates an SRQ and sets the bus error bits in its

status byte. The computer serial polls the instrument and
displays the status byte bits in proper order on the CRT. In

this example, the SRQ (B6) bit is set because of the attempt
to program an illegal command option. Other bits may be
set depending on instrument status.

Model 8573 Programming Example-

NOTE
Load the modified DECL.BAS file into the IBM
computer (see the Model 8573 Instruction

Manual) and add the following lines. Press the

return key after each line is entered.

PROGRAM

10 NA!$=“GPIBO”:CALL IBFIND

(NA$,BRDO%)

20 NA$ = “DEVO” :CALL IBFIND

(NA!$,M228 % )

30 V% =ll:CALL IBPAD

(M228%,V%)

40 V% =l:CALL IBSRE

(BRDO%,V%)

50 CMD$= “MlX”:CALL IBWRT

(M228%,CMD$)

60 CMD$ = “R9X”: CALL IBWRT

(M228 % ,CMD$)

70 l’RINT”B7 B6 B5 B4 B3 B2 Bl

BO”

80 MASK % = 128

90 CALL IBRSP(M228%,SB%)

100 FOR1 =lto8
110 IF (SB% AND MASK%) =0

THEN PRINT “0”; ELSE PRINT

“1 ”
120 MASK% =MASK%/2
130 NEXT I
140 PRINT
150 V% =O:CALL IBONL

(BRDO%,V%)

160 CALL IBONL(M228%,V%)

After the program is entered, press the

the program. After placing the instrument in remote and set­ting SRQ (line 50), line 60 attempts to program the instm-

ment into a range that does not exist (R9). At which point the

instrument generates an SRQ and sets the error and SRQ bits

in its status byte. Other bits may also be set depending on in­strument status. Lines 70, 80 and 90 display the bit positions,
set the
the instrument. Since the status byte is in decimal form, lines
100, 110, 120 and 130 are used to generate the binary
equivalent of the status byte value.

mask value to

the

most significant bit and serial poll

COMMENTS

Find the board de-

scriptor.
Find the instrument
descrptor.
Set primary address

11.
Send remote

enable.
Program for SRQ
on error.

Attempt to pro-

gram illegal com­mand option.
Identify the bits

Defind bit mask.

Conduct serial poll.

Loop eight times.

Mask off

and display them.

Close the board
file.
Close the instru­ment file.

F2

function key to run

the

bits

4-20

4.5.5 Trigger Modes (Tl

Triggering is used to tell the Model 228 to intitiate the
memory control mode sequence (single step, single cycle or
continuous). The trigger stimulus may come from commands
sent over the bus, through the external trigger input or by the
front panel START/STOP key. Triggering may be used to
either start the memory control mode sequence or stop the se­quence. The trigger modes are as follows:

TO=Start on Talk. In the TO mode, talk commands initiate
the memory control mode sequence.

228 steps through the programmed memory locations. To
send a GET command, enter the following statement into the
HP-85:

TRIGGER nl (END LINE)

Model 8573 Programming Example-Set the Model 228
to the default conditions by entering the following statements
into the IBM computer:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CALL IBCLR(M228%) (return)

Tl=Stop on Talk. In the Tl mode, talk commands stop the
memory control mode sequence.

T2 = Start on GET. In the T2 mode, a GET command (Group
Execute Trigger) initiates the memory control mode sequence.

T3=Stop on GET. In the T3 mode, a GET command stops
the memory control mode sequence.

T4= Start on X. In the T4 mode, an execute command in­itiates the memory control mode sequence.

T5=Stop on X. in the T5 mode, an execute command stops

the memory control mode sequence.

T6=Start on External Trigger-In the T6 mode, an external

trigger pulse initiates the memory control mode sequence.

T7=Stop on External Trigger-In the T7 mode, and external

trigger pulse stops the memory control mode sequence.

HP-85 Programming Example-Set the instrument to its
default conditions by entering the following statements into
the HP-85:

REMOTE 711 (END LINE)

CLEAR 7 (END LINE)

The default conditions include the trigger mode to be set for
the T6 mode. Enter the following statement to set the Model
228 to the T2 trigger mode.

OUTPUT;“T2X” (END LINE)

After the END LINE key is pressed, the Model 228 is placed in

the T2 mode (Start on GET). When a GET command is sent

by the controller to the Model 228, the instrument goes into

the selected memory control mode. For example; if memory
locations 1 through 25 are programmed for various values of

voltage current and dwell time and the single cycle mode is

selected, then when the GET command is received, the Model

The default conditions include the Model 228 set to the T6
trigger mode. To set the Model 228 to the T2 mode enter the
following statement into the IBM computer:

CMD!§=‘T2X”:CALL IBWRT(M228%,CMD$) (return)

After the return key is pressed, the Model 228 is set to the T2

trigger mode (Start on GET). When a GET command is sent
by the controller to the Model 228, the selected memory con­trol mode is initiated. For example, if memory locations 1
through 25 are programmed for various values of voltage,
current and dwell time and the single cycle memory control
mode is selected, then when GET is received the Model 228
steps through the programmed memory locations. To send
GET, enter the following statement into the IBM computer:

CALL IBTRG(M228%) (return)

4.5.6 Programmable Terminator (Y)

The Model 228 uses special terminator characters to mark the
end of its data string. To allow a wide variety of controllers to
be used, the terminator can be changed by sending the ap­propriate command over the bus. The default value is the
commonly used carriage return, line feed (CR LF) sequence.
The terminator assumes this default value upon power up,
receiving DCL or SDC command.

The terminator may be programmed by sending the ASCII

character Y followed by the desired terminator character.
Any ASCII character except one of the following may be us­ed:

1. All capital letters

2. All numbers

3. Blank

4.+-/,.ande.

4-n

Special command characters will program the instrument for
special terminator sequences as follows:

1. Y(ASCII) any ASCII except preceding list.

2. Ymn = Two terminator characters.

3. Yn = One terminator character.

4. Y(DEL) = No terminator character.

NOTE

Most controllers use the CR or LF character to
terminate their input sequences. Using a non­standard terminator may cause the controller to
hang up unless special programming is used.

HP-85 Programming Example

ments into the HP-85. To reverse the default CR LF termina­tor sequence, type the following lines into the HP-85:

REMOTE 711(END LINE)

OUTPUT 711; “Y”;CHR$(10);CHR$(13);”X”(END LINE)

When the END LINE key is pressed the second time, the nor­mal terminator sequence is reversed. The instrument termi­nates each data string or status word with a LF CR sequence.

Model 8573 Programming Example

statements to reverse the default terminator sequence.

V%=1:CALL IBSRE(BRD0%,V%) (return)

CMD$=”Y”=CHR$(10)+CHR$(13)+”X”:CALL IBWRT

(M228%,CMD$) (return)

The terminator sequence will be reversed when the second
statement is executed.

– Enter the following state-

– Use the following

W = stores the dwell time (W) value into the present memory

location.

B = selects the memory location.

A complete summary of input commands along with the for­mat of each is shown in Table 4-10. The parameter of each
command (except memory location) may be entered in direct
or scientific notation as long as the allowable range for each
command is not exceeded. Some examples of the various
command formats are as follows:

Desired Result Command Variations

1.5A Current
25V Voltage
250msec Dwell Time

Notes:

1. An IDDCO (Illegal Device-Dependent Command
Option) error occurs if the input command parameter is
outside of the legal range. A front panel error message
indicates this error. The instrument may also be
programmed to generate an SRQ if such an error occurs,
as described in paragraph 4.5.4.

2. Dwell time accuracy is valid only if the IEEE bus is idle.

3. The input command for memory location truncates any
valid variation. For example, if the command is B1.9,
then the Model 228 truncates anything to the right of the
decimal point. This means that the Model 228 selects
memory location 1.

4. To clear the memory over the bus, set the dwell time for
the first memory location to 0 (zero), for example:

I1.5; I15E-1; I.15E+1
V25; V2.5E+1; V250E-1
W250E-3; W.25; W25E-2

4.5.7 Inputs (I, V, W and B)

The input commands control the current (I), voltage (V),
dwell time (W) and the memory location (B). The input com­mands that affect Model 228 operation are as follows:

I = stores the current (I) value into the present memory

location.

V = stores the voltage (V) value into the present memory

location.

OUTPUT 711; “B1W0”

Table 4-10. Input Command Summary

Command Controls Allowable Range

Innnn
Vnnn
Wnnn
Bnnn

Current (I) Value
Voltage (V) Value
Dwell Time (W) Value
Memory Location (B)

.0001A to 10.10A
.001V to 101.0V
.02sec to 1000sec
1 to 101

4-22

HP-85 Programming Example-The following program
sets up the Model 228 output according to the values entered
from the HP-85 keyboard. Press the END LINE key after each
line is entered.

PROGRAM

10 REMOTE 711

COMMENTS

Set for remote operation.

20 DISYENTER MEM

STEP”

30 INPUT B$

Enter desired memory
location (Example: loca­tion l=Bl)

40 DISP” ENTER I”

50 INPUT I$

Enter desired current.

(Example: 2.5A = 12.5)
60 DISI”‘ENTER V”
70 INPUT V$

Enter desired voltage.

(Example: 2.5V = V2.5)
80 DISl?“ENTER W”
85 INPUT W$

Enter desired dwell

time. (Example: 250msec

= w 25)
90 OUTPUT 711;“ROFOX”, Output to IEEE bus,

“B”,B$,“I”,I$,“V”,V$ address 11.
*I~I,w$,IIy

100 GO TO 20

Repeat.

110 END

After entering the program, press the I-P-85 RUN key to start
the program. The program prompts the operator for inputs at
the appropriate points in the program. Each parameter of a
memory location is entered. To stop the program press the
PAUSE key.

PROGRAM

10 NA$ = “GPIBO” :CALL IBFIND

(NAS,BRDO%)

20 NAS = “DEVO” :CALL IBFIND

(NA!$,M228%)

30 V% =ll:CALL IBPAD

(hd228%,V%)

40 V% = l:CALL IBSRE

(BRDO%,V%)

50 1NPUT”COMMAND”; CMD$
60 IF CMD$= “EXIT” THEN 140
70 IF CMD$=” ” THEN 50

80 CALL IBWRT

(M228%,RD$)

90 RD$= Sl’ACE$(SO)

100 CALL IBRD

M228%,RD$)

110 RD$- LEFTS

(RD$,IBCNT % )

120 PRINT RD$
130 GOT0 50

140 V% =O:CALL IBONL

(BRDO%,V%)

150 CALL IBONL (M228%,V%)
160 END

COMMENTS

Find the board de­scriptor.
Find the instrument
descriptor.
Set primary address

to 11.

Send remote
enable.
Prompt for com­mand string.

See if program is to
be stopped.

If null command

string go back and

get another.
Address Model 228

to listen and send

command string.
Assign reading in-

put buffer.

Address Model 228

to listen and input

data string.
Trim string to

proper size.

Display reading on

CRT.

Repeat.

Close the board
file.
Close the instrument

file.

Model 8573 Programming Example-The following pro­gram sends a command string to the Model 228 and displays
the instrument data string on the IBM CRT.

NOTE
Load the modified DECL.BAS file into the IBM
computer (see the Model 8573 Instruction
Manual) and add the following lines.

After entering the program press the F2 function key to run
the program. The CRT prompts the operator for the desired
commands and then displays the data string on the CRT.

4-23

4.5.8 Function (F)

The function commands control the actual output of the
Model 228. These commands perform the same operation as

the front panel OPERATE/STANDBY key. The output may

be controlled by bus commands as follows:

death. Always turn the instrument to stand­by, let it cool down and then turn it off
before coming into contact with the output

terminals of the Model 228.

4.5.9 Range (RI

FO (Standby) =The output terminals are programmed to +4

counts on the present range. Refer to paragraph 2.2.1 for
details concerning the standby mode.

Fl (Operate)=The output terminals are programmed to the
present value of voltage and current.

HP-85 Programming Example-Using the front panel
OPERATE/STANDBY key, place the instrument in the
standby mode and enter the following statements into the
HP-85 :

REMOTE 711 (END LINE)

OUTPUT T11;“FlX” (END LINE)

When the END LINE key is pressed the second time, the front
panel OPERATE LED turns on and the instrument is placed in

the operate mode. Do not leave the instrument in the operate
mode unattended. Always place the instrument in standby

after the measurement or test is completed.

WARNING

Do not come into contact with any live cir-

cuit that could cause personal injury or

The range commands set the maximum allowable current that
may be programmed into the instrument. Table 4-11 shows

the range commands. Upon power up, or after a DCL or

SDC, the RO (AUTO) mode is enabled.

1. On a given range, the source parameter can be no larger
than the range will allow.

2. If an under range command is given, a zero source value is

stored.

3. If an overrange command is given, the instrument

responds with a front panel IDDCO (Illegal Device­Dependent Command Option) error as described in
paragraph 4.5.4.

HP-85 Programming Example-The following program
sets the Model 228 to the IV, 1OA range and then gives an in­put command of 758mV. The program stops at this point and
prompts the user to continue the program. Once the program
is running again the controller sends an illegal device­dependent command option (W) to the instrument. Then the
program displays an IDDCO on the instrument as well as on
the HP-85 CRT.

NOTE

After entering each line press the END LINE key.

424

Range

Command

RO
Rl
R2
R3
R4
R5
R6
R7
R8

Table 4-11. Range Commands

Maximum

Ranae
Auto

lV, 100mA
lV, 1A
lV, 10A
IOV, 100mA
lOV, 1A
lOV, 1OA
lOOV, IOOmA
lOOV, 1A

output

lV, 100mA
lV, 1A
IV, 1OA
IOV, lOOmA
lOV, IA
lOV, 10A
lOOV, IOOmA
lOOV, 1A

Minimum

Step

lmV, IOjiA
lmV, lOOpA
ImV, 1mA
IOmV, 1Ofl
lOmV, 1OOfi
IOmV, 1mA
1 OOmV, 10,uA
lOOmV, lOOpA

PROGRAM COMMENTS

PROGRAM

COMMENTS

10 REMOTE 711 @ CLEAR Set up for remote operation

and clear the screen.

20 CLEAR nl

Return to the default condi­tions

30 0uTRlT 711; Set the Model 228 to the

“R3MlDOX”

lV, 1OA range turn on SRQ
and display Volts, Amps.

40 OUTPUT 7ll;‘Y.75X

Program the Model 228 to

750mv.
50 DISP” PRESS CONT”
60 PAUSE
70 OUTPUT 7ll;‘V5X’ Attempt to program illegal

voltage on this range.
80 S=SPOLL (7ll) Conduct serial poll.
90 IF BIT(S,S) AND BIT(S,l) Check for IDDCO.

=1 THEN DISI”‘ILLE­GAL COMMAND OP­TION“

100 OUTPUT nl;“ROX” Set to autorange.
110 END

After entering the program, press the RUN key. The program

sets the Model 228 to the lV, 1OA range and programs for a
voltage of 75OmV. Press the CONT key and observe that the
instrument displays IDDCO. The IDDCO is also displayed
on the CRT because the status byte was checked by the com­puter when the error IDDCO bits were set.

10 NA$=“GPIBO”:CALL IBFIND

(NA!$,BRDO%)

20 NAS= “DEWYCALL IBFIND

(NA$,ht228%)

30 V% =ll:CALL IBPAD

(Ivf228%,V%)

40 V% =l:CALL IBSRE

(BRDO%,V%)

50 CALL IBCLR(M228%)
60 CMD$ = “R3MlXDO”:CALL

IBWRT(M228 % ,CMD$)

70 CMD$ = “V.75X”:CALL IBWRT

(M228%,CMD$)

80 CMD$ = “V5X”: CALL IBWRT

@4228%,CMD$)

90 CALL IBSRI’

(M228%,SB%)

100 PRINT SB%

110 CMD$ = “ROX”: CALL IBWRT

(h&28% ,CMD$)

120 V% = :CALL IBONL

(BRDO%,V%)

130 CALL IBONL

(M228%.V%)

Find the board de­scriptor.
Find the instrument
descriptor.
Set primary address
to 11.
Set remote enable.

Set to default condi­tions.
Set to lV, 1OA
range turn on SRQ

and display Volts,

Amps.
Program the

750mv.
Attempt to program
illegal voltage on
this range.
Conduct serial poll.

Display data.

Set to autorange.
Close board file.
Close instrument

file.

It is important to note that the commands in line 70 would be
valid if the instrument were set to the proper range. This is
taken care of automatically in the RO mode, since the instru­ment changes to the appropriate range, depending on the
commanded value. To demonstrate this point, change line 30

to OUTPUT 7ll; ‘ROMW and run the program again. This
time the commands in line 70 are accepted by the insrument

since it remains in the autorange mode.

Model 8573 Programming Example-The following pro­gram sets the Model 228 to the lV, lOA range and then gives
an input command of 750mV. The program stops at this
point and prompts the user to continue the program. Once
the program is running again the controller sends an illegal
command option (SV) to the instrument. Then the program
displays an IDDCO on the instrument as well as on the CRT.

NOTE
Load the modified DECL.BAS file into the IBM
computer (see the Model 8573 Instruction
Manual) and add the following lines. After each
line is entered press the return key.

After entering the program, press the F2 function key to run

the program. The program sets the Model 228 to the lV, 1OA
range and sets 750mV. Then the program attempts to set the
instrument to 5V. This value is outside of the selected range

and causes the IDDCO message to be displayed on the instru­ment. A serial poll is conducted and an SRQ reveals the
IDDCO. The computer also displays the data.

It is important to note that the commands in line 80 would be

valid if the instrument were set to the proper range. This is

taken care of automatically in the RO mode, since the instru-

ment changes to the appropriate range depending on the com-

manded value. To demonstrate this point, change line 60 to:

60 CMD$=“R3MlX”:CALL

Run program.

IBWRT(M228 % ,CMD$)

This time the commands in line 80 are accepted by the instru-

ment since it remains in the autorange mode.

4.5.10 External Modulation (A, C)

HP-85 Programming Example-To enable the sink mode
over the bus, enter the following statements into the HP-85:

The external modulation mode may be enabled or disabled

over the bus. In external modulation, an external AC signal is
applied to the external modulation connector and therfore the
output. Current or voltage may be modulated as can be seen
by the front panel LEDs (MODULATE V and MODULATE
I). The commands for external modulation are as follows:

AO-Turn off voltage modulation.
Al-Modulate voltage.

CO-Turn off current modulation.
Cl-Modulate current.

HP-85 Programming Example-To turn on the modulate
current function enter the following lines into the I-II’-85:

REMOTE nl (END LINE)

OUTPUT 7ll;“AlX” (END LINE)

After the END LINE key is pressed the second time, the
Model 228 is placed in the modulate current mode.

Model 8573 Programming Example-To turn on the
modulate current function enter the following lines into the
IBM computer.

REMOTE 7H (END LINE)

OUTPUT 7Il;“SlX” (END LINE)

After the END LINE key is pressed the second time, the
Model 228 is placed in the sink mode. The front panel SINK
ONLY LED turns on. The Model 228 high power supply is
decreased and the instrument can dissipate full power con­tinuously at 50°C with no derating.

Model 8573 Programming Example-To enable the sink
mode over the bus, enter the following statements into the
IBM computer:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$= “SlX”:CALL IBWRT(M228%,CMD$) (return)

After the return key is pressed the second time, the Model 228
is placed in the sink mode. The front panel SINK ONLY LED
turns on. The Model 228 high power supply is decreased and
the instrument can dissipate full power continuously at 50°C
with no derating.

4.5.12 Status Word NJ)

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$=“AlX”:CALL IBWRT(M228%,CND$) (return)

After the return key is pressed the second time, the Model 228

is placed in the modulate current mode.

4.5.11 Sink Mode (S)

The Model 228 may be operated in the sink mode. That is,

power is delivered to the Model 228. The sink program allows

the instrument to decrease the high power supply and still

operate as an active load. With the supply reduced, the
Model 228 can dissipate full power continuously at SO’C with

no derating. Refer to paragraph 3.13.4 for details concerning

the sink mode. The commands to enable the sink mode are as

follows:

SO=Disable sink mode.

Sl = Enable sink mode.

The status word command allows access to information con­cerning various operating modes of the instrument. When the
UO command is given, the instrument outputs the status word

the next time it is addressed to talk. The status word is sent in-

stead of the normal data string. The status word is sent only

once each time the UO command is given. The command for
the status word to be sent is as follows:

UO=Send Status Word. The format is the Model number

(228) followed by five bytes representing the modes and func­tions of the Model 228. Information concerning all modes ex­cept for SRQ are one byte in length.

Ul=Send Error Status Word. The format is the model

number (228) followed by five bytes representing the various
errors.

Figure 4-7 shows the general format of the error status word.
The figure shows the errors of the word. Figure 4-8 shows the
general format of the status word. The figure shows the
default values. The letters correspond to modes programmed
by the respective device-dependent commands.

4-26

Note that all returned values except for those associated with
the terminator correspond to the programmed numeric

values. For example, if the instrument is presently in the R3
range, the R byte in the status word will correspond to an
ASCII 3.

NOTE

After each line is entered, press the END LINE
key.

PROGRAM COMMENTS

Notes

1. The status word should not be confused with the SRQ
status byte. The status word contains a number of bytes
pertaining to the various operating modes of the instru­ment. The status byte is a single byte that is read by using
the serial polling sequence and contains information on
SRQ status and error or data conditions.

2. To make sure proper status is returned, the status word
should be read immediately after sending the command.
Otherwise, instrument status may change, resulting in er­roenous status information.

3. The status word is sent only once each time the status com­mand is given. Once the status is read, the instrument
sends the normal data string the next time it addressed to
talk.

4. The SRQ status information contains several bytes. These
bytes assume the decimal value previously set by the SRQ
mode command.

HP-85 Programming Example-To

output the status word

enter the following program into the I-P-85:

- 1 SINK (OFF)

10 REMOTE nl Set up for remote operation.
20 CLEAR 7

Clear the Model 228.
30 OUTPUT 711;“UOX” Output status word.
40 ENTER nl;A$ Obtain data string.
50 DISP A$ Display data string.
60 END End of program.

After the program is entered into the computer, press the

HP-85 RUN key to run the program. After pressing the RUN
key, the Model 228 outputs the status word. In this case, the
status is transmitted to the controller with a prefix.

I

228000000

Calibration Error

High Temperature Warning

Overflow Reading

Not in remote

IDDCO

IDDC

Figure 4-7. Error Status Word

PREFIX

DISPLAY (D=O) VOLTS/AMPS

FUNCTION (F=O) STANDBY

PREFIX (&O) BUFFER

BUFFER LOCATION CUTPUT

SELF lEST

(DEPENDENT ON TEST)

SEND EOI

SINGLE CYCLE MODE

(K=O) ­(P=O)

-v SOURCE (OFF)

+ ‘SINK (OFF)

228DFGJKPRTACSMMOOOOO

SRQ DISABLED (k&O)

PREVIOUSLY
PROGRAMMED

VALUES OF MEMORY

-

-1

LOCATION #I

STARTON EXTERNAL TRIGGER
AUTORANGE (R=O)

Figure 4-8. Status Word Format

TRIGGER (T=6)

4-27

Model 8573 Programming Example--To output the status

word enter the following program into the IBM computer.

NOTE
Load the modified DECL.BAS file into the IBM
computer (see the Model 8573 Instruction
Manual) and add the following lines. After each
line is entered press the return key.

PROGRAM

10 NA$=“GPIBO”:CALL IBFIND Find the board de-

(NA!§,BRDO%)

20 NA$ = “DEVO”: CALL IBFIND

(NA!Ji,M228%)

30 V% =ll:CALL IBPAD

(M228%,V%)

40 V% =l:CALL IBSRE

(BRDO%,V%)

50 CMD$ = “UOX”: CALL IBWRT

(M228%,CMD!§)

60 RD$=SPACE(SO):CALL IBRD Obtain data string.

(M228%,RD$)
70 PRINT RD$
80 V% =O:CALL IBONL

(BRDO%,V%)
90 CALL IBONL

(M228%,V%)

COMMENTS

scriptor.
Find the instrument
descriptor.
Set primary address
to 11.
Send remote enable.

Output status word.

Display data string.
Close the board file.

Close the instrument
file.

3. After steps 1 and 2, the Model 228 displays the present
software level.

4. After step 3, the Model 228 displays the present primary
address.

5. After step 4, the Model 228 goes through the autocalibra­tion cycle and displays the CAL message.

6. After step 6, the Model 228 is ready for operation.

NOTE

The self test (J) over the bus, performs the exact

same sequence as Program 6. The messages are
also the same. Refer to paragraph 3.11.6.

4.514 EOI and Bus Hold-Off Modes (KI

The K command controls whether the instrument sends the
EOI command at the end of its data string; and whether busy
activity is held off (through the NRFD line) until all com­mands sent to the instrument are internally processed once
the instrument receives the X character. K command options
include:

KO=Send EOI with last byte; hold off bus on X.

Kl=Do not send EOI with last byte; hold off bus on X.
K2 = Send EOI with last byte; do not hold off bus on X.

After the program is entered, press the F2 function key to run
the program. After pressing the F2 key the Model 228 outputs
the status word and it is displayed on the CRT.

Upon power up, or after the instrument receives a DCL or
SDC command, the KO mode is enabled.

4.5.13 Self Test (J)

The letter J is the command that programs the Model 228 to
go through many of the testing routines that are automatical­ly performed upon power up. When the J command is sent
the following routines are performed:

1. All of the front panel LEDs turn on. This is a display test.
The user can note inoperative display segments or in­dividual LEDs by observing the front panel.

2. During the display test, the Model 228 performs a check on
the RAM circuitry and a cyclic redundancy check (CRC)
on the ROM circuitry. If a problem is found with either of
these two tests, then the appropriate messages are
displayed and the J byte in the status word is set.

K3=Send no EOI with last byte; do not hold off bus on X.

The EOI line on the IEEE-488 bus provides a method to
positively identify the last byte in a multi-byte tranfer se-

quence. Keep in mind that some controllers rely on EOI to
terminate their input sequences. In this case, suppressing EOI
with the K command may cause the controller’s input se-

quence to hang up unless other terminator sequences are
used.

The bus hold off mode allows the instrument to temporarily

hold up bus operation when it receives the X character until
it processes all commands sent in the command string. Keep

in mind that all bus operation will cease, not just activity
associated with the Model 228. The advantage of this mode is
that no bus commands will be missed while the instrument is
processing commands previously received.

The hold off period depends on the commands being process-

ed. Table 4-12 lists hold off times for a number of different
commands. Since a NRFD hold off is employed, the hand­shake sequence for the X character is completed, and no bus

hang up occurs under these conditions.

4-28

HP-85 Programming Example-To program the instru­ment for the K2 mode, enter the following statements into the
HP-85:

Device-dependent commands are sent as a string of several
ASCII characters. Some examples of valid command strings
include:

REMOTE nl (END LINE)

OUTPUT nl;“KW (END LINE)

When the second statement is executed, the instrument will be
placed in the K2 mode. In this mode, EOI will still be

transmitted at the end of the data string, but the bus hold-off

mode will be disabled.

Model 8573 Programming Example-To place the instru-

ment in the K2 mode, enter the following statements into the

IBM computer:

V% =l:CALL IBSRE(BRDO%,V%) (return)

CMD$ = “K2X”:CALL IBWRT(M228 % ,CMD$) (return)

The Model 228 will be placed in the K2 mode when the se­cond statement is executed. The EOI mode will be enabled,
but the bus hold off will be disabled.

Table 4-12. Hold Off Times

Command
V, I, B, W

X Hold Off

46msec

FOX = Single command string.
FOM2POR4X=Multiple command string.
R7 X = Space is ignored.

Some examples of invalid command strings are:
@OX=Invalid command; @ is not a command.

D6X=Invalid command option; 6 is not an option of the D
command.

The numbers after the command are each interpreted as a
decimal integer. For example:

TOlOX is interpreted as TlX

Figure 4-9 shows the front panel error messages used by the
Model 228. The message in Figure 4-9A results from an illegal
device-dependent command (IDDC), while the message in
Figure 4-9B results from an illegal device-dependent com­mand option (IDDCO). The no remote message in Figure
4-9C results from attempting to program the instrument when
it is not in the remote mode.

All other device-dependent commands
(A, C, D, etc.)

43msec

4.6 FRONT PANEL ERROR MESSAGES

The process of programming the Model 228 involves the pro­per use of syntax. Syntax is defined as the orderly systematic
arrangement of programming commands or languages. The
Model 228 must receive value commands with the proper
syntax or the instrument goes through the following se­quence.

1. Ignore the entire command string in which the invalid com­mand appears.

2. Set appropriate bits in the status byte.

3. Generate an SRQ if programmed to do so.

4. Display an appropriate front panel error message.

C

Figure 4-9. IEEE Display Error Message

4-29