Keithley 230, 220 User Manual

Model 220,230

Programming Manual

Contains IEEE Programming Information

WARRANTY

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

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1 o/99

Model 220 Programmable Current Source Model 230 Programmable Current Source

Programming Manual

01982, Keithley Instruments, Inc.

Cleveland, Ohio, U.S.A.

Third Printing, May 2000

Document Number: 220-900-01 Rev. C

SPECIFICATIONS

IEEE-488 BUS IMPLEMENTATION:

Multiline Commands: DCL, LLO, SDC, GET, GTL, UNT, UNL, SPE, SPD. Uniline Commands: IFC, REN, EOI, SRQ, ATN. Interface Functions: SHl, AHl, T6, TE6, L4, LH), SRl, RLl, PW, DCl, DTl, CO, El. Internal Programmable Parameters: DISPLAY MODE, OUTPUT, Prefix (Data Format), EOl, SRQ (including mask for over limit), PROGRAM MODE,

Range, Trigger Mode, Terminator Character, Inputs (SOURCE, LIMIT, DWELL TIME, 106Point Memory Locations), Output Status, Digital Self Test. Digital l/O Port: A separate I/O port consisting of four input and four output lines as well as common (IEEE4881 and + 5VDC. Outputs will drive one

TTL load. Inputs represent one TTL load. The 220/230 can be programmed to generate a “SRQ” upon any change in the four bit input data.

Mating connector supplied.

IEEE COMMAND GROUPS

ADDRESS COMMAND GROUP

LISTEN: LAG = LISTEN ADDRESS GROUP

MLA = MY LISTEN ADDRESS UNL= UNLISTEN

TALK: TAG =TALK ADDRESS GROUP

MTA = MY TALK ADDRESS UNT = UNTALK OTA=OTHER TALK ADDRESS

ADDRESSED COMMAND GROUP

ACG = ADDRESSED COMMAND GROUP GET= GROUP EXECUTE TRIGGER GTL = GO TO LOCAL SDC = SELECTIVE DEVICE CLEAR

STATUS COMMAND GROUP

RQS = REQUEST SERVICE SRQ= SERIAL POLL REQUEST STB = STATUS BYTE

HANDSHAKE COMMAND GROUP

DAC = DATA ACCEPTED RFD=READY FOR DATA DAV = DATA VALID

UNIVERSAL COMMAND GROUP

ATN = ATTENTION DCL= DEVICE CLEAR IFC = INTERFACE CLEAR LLO = LOCAL LOCKOUT REN = REMOTE ENABLE SPD = SERIAL POLL DISABLE SPE = SERIAL POLL ENABLE

END = EOI

Display:

Function:

Prefix:

(Data Format)

EOI:

SRQ:

Program:

Range:

DO Dl D2 D3

Fo Fl

GO Gl

G3 G4 G5

M(O-31)

PO Pl P2

RO Rl R2

I?3 R4 R5 R6

DEVICE DEPENDENT COMMAND GROUP

Source Limit Dwell Time Memory Location

Standby Operate

Location With Prefix Location Without Prefix Buffer Address With Prefix Buffer Address Without Prefix Full Buffer With Prefix Full Buffer Without Prefix

Send EOI Send No EOI

Disabled: IDDC or IDDCO: Over Limit: End of

Buffer;‘End of Dwell Time; No Remote; Input Port Change

Single Continuous Step

Auto 1nA (220); 100mV (230)

1OnA (220): 1V (230) 100nA (220); 1OV (230)

14 (220); 1OOV (230) 1ofi f220) 100&A (220)

Trigger:

Terminator:

Inputs:

I/O Port:

status:

Digital Self Test:

Execute:

R7 R8 R9

TO Tl

T4 T5 T6 3-7

YIASCII)

YILF)

YfCR)

Y(DEL)

0015) uo

Ul JO

1mA (220) 1OmS (220) lOOmA (220)

Start On Talk Stop On Talk Start On GET Stop On GET StartOnX Stop On X Start On External Trigger Stop On External Trigger

Any ASCII except capitals, numbers, + - /,.e CR LF LF CR None

Current Source (220); Current Limit (230) Vottage Limit (220); Voltage Source (230) Dwell Time Buffer Address Memory Location

Set Output Control Bits Status Word

I/O Port status

Execute Command

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 the operating information carefully before using the product.

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, 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.

Users of this product must bc protcctcd from electric shock at all times. The responsible body must ensure that users arc prevented access and/or insulated from every connection point. In some cases, connections must be exposed to potential human contact. Product users in these circumstances must bc trained to protect thcmsclves from the risk of electric shock. If the circuit is capable ofopcrating at or above 1000 volts. no conductive part of the circuit may be

exposed.

As described in the Intcmational Electrotechnical Commission (IEC) Standard IEC 664, digital multimctcr measuring circuits (e.g., Keithley Models I75A, 199,2000,2001, 2002. and 2010) arc Installation Category II. All other instruments’ signal terminals arc Installation Category I and must not bc connected to mains.

Do not connect switching cards directly to unlimited power circuits. They are intended to bc 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 connccted to a properly grounded power receptacle. Inspect the connecting cables, test leads, and jumpers for possible wear. cracks, or breaks before each use.

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 cntirc 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.

Exercise extreme caution when a shock hazard is present. Lethal

voltage may be present on cable connectorjacks 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.

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.

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.

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 fat measuring circuits, NOT as safety earth ground connections.

If you are using a test fixture, keep the lid closed while power is ap-

plied to the device under test. Safe operation requires the use of a

lid interlock.

Ifa@

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 re-

fer to the operating instructions located in the manual.

The

symbol on an instrument shows that it can source or mea-

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

Instrumentation and accessories shall not bc conncctcd 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 Icads. and input jacks, must be purchased from Keithlcy 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 bc purchased from other suppliers as long as they are equivalent to the original component. (Note that se-

lectcd parts should be purchased only through Keithley Instruments to maintain accuracy and functionality of the product.) If you arc 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 in-

structions. If the board becomes contaminated and operation is af-

fected, the board should be returned to the factory for proper

cleaning/servicing.

Rev. IO/99

TABLE OF CONTENTS

Paragraph

1 .I

1.2

1.3

1.4

1.5

1.6

1.7

2.1

2.2

2.3

2.3.1

2.3.2

2.3.3

2.4

2.4.1

2.4.2

2.4.3

2.4.4

2.4.5

2.5

2.6

2.6.1

2.6.2

2.6.3

3.1

3.2

3.2.1

3.2.2

3.2.3

3.2.4

3.3

3.3.1

3.3.2

3.3.3

3.3.4

4.1

4.2

4.2.1

4.2.2

4.2.3

4.2.4

4.2.5

4.2.6

4.2.7

4.2.8

4.3

4.3.1

4.3.2

4.3.3

4.3.4

4.3.5

4.3.6

4.3.7

SECTION 1 - GENERAL INFORMATlON

introduction Model 220 and 230 IEEE Interface Features..

Warranty Information.. ...................................................................................................................................................................................

Manual Addenda.. .........................................................................................................................................................................................

Safety Symbols and Terms ...........................................................................................................................................................................

Using the Model 220/230 Programming Manual. ..........................................................................................................................................

IEEE Specifications

SECTION 2 - AN OVERVIEW OF THE IEEE-488 BUS

Introduction

Bus Description.. ...........................................................................................................................................................................................

IEEE-488 Bus Lines.. ....................................................................................................................................................................................

Bus Commands.. ...........................................................................................................................................................................................

Command Codes Command Sequences

SECTION 3 - SYSTEM CONFIGURATION

Introduction ...................................................................................................................................................................................................

Hardware Considerations.. ............................................................................................................................................................................

Software Considerations.. .............................................................................................................................................................................

SECTION 4 - OPERATION

General Bus Commands.. .............................................................................................................................................................................

Device-Dependent Command Programming ................................................................................................................................................

Title Page

...................................................................................................................................................................................................

..............................................................................................................................................

.......................................................................................................................................................................................

............................................................................................

Bus Management Lines

Handshake Lines ..................................................................................................................................................................................

Data Lines

Uniline Commands.. Universal Commands.. Addressed Commands

Unaddressed Commands .....................................................................................................................................................................

Device-Dependent Commands.. ...........................................................................................................................................................

Addressed Command Sequence.. ........................................................................................................................................................

Universal Command Sequence ............................................................................................................................................................

Device-Dependent Command Sequence

Typical Systems

Bus Connections ..................................................................................................................................................................................

Primary Address Selection

Digital I/O Port.. .....................................................................................................................................................................................

Controller Interface Routines ................................................................................................................................................................

HP-85 BASIC Statements..

Interface Function Codes ......................................................................................................................................................................

Model 220/230 Interface Commands. ...................................................................................................................................................

REN (Remote Enable) ..........................................................................................................................................................................

IFC (Interface Clear). .............................................................................................................................................................................

LLO (Local Lockout). .............................................................................................................................................................................

GTL (Go To Local). ................................................................................................................................................................................

DCL (Device Clear). ..............................................................................................................................................................................

SDC (Selective Device Clear). ..............................................................................................................................................................

GET (Group Execute Trigger) ...............................................................................................................................................................

Serial Polling (SPE, SPD) .....................................................................................................................................................................

Execute (X)

Display Mode (D) ..................................................................................................................................................................................

Inputs (I, V, W, L, B). ..............................................................................................................................................................................

I/O Port (0) ...........................................................................................................................................................................................

Function (F). ..........................................................................................................................................................................................

Data Format (G). ...................................................................................................................................................................................

EOI Programming (K) ...........................................................................................................................................................................

.............................................................................................................................................................................................

..........................................................................................................................................................................................

...........................................................................................................................................................................................

........................................................................................................................................................................

..............................................................................................................................................................................

.........................................................................................................................................................................

..................................................................................................................................................................................

.............................................................................................................................................

....................................................................................................................................................................................

...................................................................................................................................................................

. ......................................................................................................

1-l l-l l-l l-l l-1 l-l 1-l

2-l 2-l 2-l 2-l 2-2 2-2 2-3 2-3 2-3 2-3 2-3 2-3 2-4 2-4 2-6 2-6 2-6

3-1 3-1 3-l 3-l 3-3 3-4 3-4 3-4 3-5 3-5 3-6

4-l 4-l 4-l 4-l 4-2 4-2 4-2 4-3 4-3 4-3 4-4 4-6 4-6 4-6 4-8 4-8

4-8

4-10

TABLE OF CONTENTS (CONT.)

Paragraph

4.3.8

4.3.9

4.3.10

4.3.11

4.3.12

4.3.13

4.3.14

4.4

4.4.1

4.4.2

4.4.3

4.5

4.5.1

4.5.2

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

5.10

5.11

Front Panel

Waveform

SECTION 5 - IEEE COMMAND FLOW CHARTS

DCL (Device Clear).

IFC (Interface Clear) REN

Serial

UNL UNT (Untalk)

GET

GTL SPC (Selective Device Clear)

Device-Dependent Commands..

Title

SRQ Mode (M) and Status Byte Format.. Program Mode (P)

Range (R) .............................................................................................................................................................................................

Trigger Mode (T) ...................................................................................................................................................................................

Programmable Terminator (Y). ..............................................................................................................................................................

Status Word (U) ....................................................................................................................................................................................

Digital Self-Test (J). ...............................................................................................................................................................................

Error Messages .........................................................................................................................................................................

IDDC Error.. ..........................................................................................................................................................................................

IDDCO Error .........................................................................................................................................................................................

No Remote Error..

Programs

Sine Wave Approximation .....................................................................................................................................................................

Ramp Simulation.. .................................................................................................................................................................................

(Remote Enable) ..................................................................................................................................................................................

Polling (SPE, SPD)

(Unlisten). ..............................................................................................................................................................................................

.................................................................................................................................................................................................

(Group Execute Trigger).

(Go To Local). ........................................................................................................................................................................................

................................................................................................................................................................................

.................................................................................................................................................................................

......................................................................................................................................................................................

.....................................................................................................................................................................................

.............................................................................................................................................................................

.......................................................................................................................................................................

...................................................................................................................................................................

.............................................................................................................................................

Page

4-10 4-13 4-13 4-14 4-15 4-15 4-17 4-17 4-18 4-18 4-18 4-18 4-18 4-19

5-1 5-1 5-1 5-1 5-2 5-2 5-3 5-3 5-4 5-4 5-4

LIST OF TABLES

Table

2-l 2-2 2-3 2-4

3-l 3-2 3-3 3-4 3-5 3-6 4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10

Figure

Title Page

IEEE-488 Bus Command Hexadecimal and

Typical Addressed Command Sequence ...................................................................................................................................................... 2-6

Typical Device-Dependent Command Sequence.. IEEE Contact Designations..

Primary Address Switch Positions ................................................................................................................................................................ 3-3

Digital I/O Port Pin Assignments

HP-85 IEEE-488 Basic Statements .............................................................................................................................................................. 3-5

Model 220/230 Interface Function Codes .....................................................................................................................................................

IEEE Command General Bus Command..

Default Values (Status on

Device-Dependent Command Summary

Model 220 and 230 Display Mode Commands .............................................................................................................................................

Input Command Summary

l/O Port Command Parameters

SRQ Commands and Conditions

Status Byte Data and Error Conditions. ........................................................................................................................................................

Range Commands

I/O Port Status Values..

Groups ...............................................................................................................................................................................

Summary

Decimal Command

...............................................................................................................................................................................

Power Up and After SDC or DCL) .......................................................................................................................

............................................................................................................................................................................

........................................................................................................................................................................................

.................................................................................................................................................................................

............................................................................................................................................................. 2-4

.........................................................................................................................................................................

...................................................................................................................................................................

.....................................................................................................................................................................

..................................................................................................................................................................

...............................................................................................................................................

Codes

........................................................................................................................................

......................................................................................................................................................

2-4

2-6 3-2

3-4

3-6 3-6 4-l 4-3 4-5 4-6 4-7

4-8 4-11 4-12 4-13 4-16

LIST OF FIGURES

Title Page

2-l 2-2 2-3 3-1

3.2 3-3 3-4 3-5 3-6 3-7

3-8 4-1 4-2 4-3

4-4

4-5 4-6 5-1 5-2 5-3 5-4 5-5 5-6 5-7 5-8 5-9 5-10

IEEE Bus Configuration

IEEE Handshake Sequence.. ........................................................................................................................................................................

Command Codes System Types IEEE-488 Connector.. IEEE-488 Connections.. Rear Panel of Model 220 or 230 Showing IEEE Connectors and Switches Contact Assignments..

Typical IEEE-488 Bus Driver (One of 16). .....................................................................................................................................................

Primary Address Switches (Address = 12 Shown)

Digital I/O Port Pin Assignments.. .................................................................................................................................................................

Model 220 and

SRQ Mask Format ........................................................................................................................................................................................

Status Byte Format Status Word Format (Default Values Shown) I/O Status Format (Default Values Front Panel Error Messages DCL Command Flow Chart IFC Command

REN Command Flow Chart ..........................................................................................................................................................................

Serial Poll Flow Chart.. UNL Command Flow Chart..

UNT Command GET Command Flow Chart. GTL Command

SDC Command

Device-Dependent Command Flow Chart ....................................................................................................................................................

................................................................................................................................................................................................

230 Data

Flow Chart

................................................................................................................................................................................

.........................................................................................................................................................................................

...................................................................................................................................................................................

................................................................................................................................................................................

..................................................................................................................................................................................

.......................................................................................................................................

Formats.. ...............................................................................................................................................................

.......................................................................................................................................................................................

Shown).

.........................................................................................................................................................................

...........................................................................................................................................................................

............................................................................................................................................................................

..................................................................................................................................................................................

.........................................................................................................................................................................

Flow Chart.. .........................................................................................................................................................................

Flow Chart..

Flow Chart

..........................................................................................................................................................................

.........................................................................................................................................................................

..........................................................................................................................................................................

................................................................................................................................................

...................................................................................................................................................

.................................................................................................

2-2 2-2 2-5 3-l 3-l 3-2 3-2

3-2 3-3 3-3 3-4

4-9

4-12 4-12

4-l 6 4-16 4-l 8

5-l 5-l 5-2 5-2 5-3 5-3 5-4

5-4 5-5 5-5

iii/iv

SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

The Model 220 programmable current source, and the Model 230 programmable voltage source are each supplied with a standard IEEE-488 interface. This interface adds an extra measure of versatility by allowing the transmission of data and commands over the IEEE-488 bus. The built-in IEEE interface provides all the logic necessary to interface the Models 220 and 230 to the bus using standard IEEE-488-1978 protocol. Additionally, the interface board incorporates a separate digital I/O port that may be used to interface the Models 220 and 230 to other digital instrumentation.

1.2 MODEL 220 AND 230 IEEE INTERFACE FEATURES

Important IEEE-488 interface features include:

1. IEEE-4881978 Standard. The Model 220 or 230 communicates with other instrumentation using the same IEEE488-1978 standards.

2. Standard IEEE Connector. A standard IEEE-488 connector is available on the rear panel of the instrument for easy connection to the IEEE bus.

3. Simple Primary Address Selection. The primary address of the Model 220 or 230 may be easily changed by using the five address switches on the rear panel of the instrument.

4. Digital I/O port. The interface also includes a digital I/O port which has separate 4-bit input and output connections. Port status may be read and controlled through commands given over the IEEE bus.

5. Programming Versatility. All Model 220/230 operation is supported by IEEE programming. In addition, numerous other IEEE commands add operating features not available from the front panel.

1.3 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 proper course of action.

Keithley Instruments, Inc. maintains service facilities in the

United States, United Kingdom, and throughout Europe. Addresses for 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 applications engineer at any of these locations.

1.4 MANUAL ADDENDA

Information concerning improvements or changes to the instrument which occur after the printing of this manual

may be found on an addendum included with this manual. Be sure to review these changes before attempting to program the instrument.

1.5 SAFETY SYMBOLS AND TERMS

The following safety symbols and terms are used in this

manual and may be found on the Model 220 and 230:

The symbol ’ user should refer to the operating instructions.

The symbol potential of 1OOOV or more may be present on the terminal(s). Standard safety precautions should be observed when such dangerous voltages are encountered.

information associated with the WARNING heading explains dangers that could result in personal injury or death.

Information following the CAUTION heading explains hazards that could damage the instrument.

1.6 USING THE MODEL 220/230 PROGRAMMING MANUAL

This manual contains all the information necessary to con-

nect the Model 220 or 230 to the IEEE488 bus and program the instrument from a separate bus controller. Not included in this manual is information concerning front panel operation, servicing, or maintenance of the instrument {including the interface board itself). For those aspects, refer to the Model 220 or 230 Instruction Manual.

This programming manual is divided into the following sections:

1. Section 2 contains a general description of the IEEE-488

bus and its commands.

2. information necessary to connect the instrument to the

bus and set the primary address is contained in Section 3. Also, digital I/O port information can be found in this section.

3. The bulk of the programming information may be found in Section 4. General bus commands as well as commands unique to the Models 220 and 230 are covered in detail.

4. Section 5 contains IEEE command flow charts, which could be helpful in some applications.

1.7 IEEE SPECIFICATIONS

A complete list of IEEE specifications is presented immediately preceding this section.

on the instrument indicates that the

on the instrument indicates that a

l-1/1-2

SECTION 2

AN OVERVIEW OF THE IEEE-488 BUS

2.1 INTRODUCTDON

The IEEE-488 bus is an instrumentation data bus adopted by the IEEE WWitute of Electrical and Electronic Engineers) in 1975 and given the IEEE488 designation. The most recent revision of bus standards was made in 1978; hence the complete description for current bus standards is the IEEE-488-1978 designation.

This section gives a brief description of the general bus structure along with an outline of bus commands. The information presented here is not intended to be an in-depth description of what is truly a very complex set of standards. More complete information on the IEEE-488 bus, which is also frequently referred to as the GPIB (General Purpose Interface Bus), is available from the IEEE and a variety of other sources.

2.2 BUS DESCRIPTION

The IEEE-488 bus was designed as a parallel data transfer medium to optimize data transfer without using an excessive number of bus lines. In keeping with this goal, the bus has only eight data lines that are used for both data and some commands. Five bus management lines and three handshake lines round out the complement of signal lines. Since the bus is of parallel design, all devices connected to the bus have the same information available simultaneously.

Exactly what is done with the information by each device

depends on many factors, including device capabilities.

A typical bus configuration for controlled operation is shown in Figure 2-1. The typical system will have one controller and one or more instruments to which commands are given and, in most cases, from which data is received. Generally, there are three categories that describe device

operation. These designations include: controller; talker: listener.

The controller does what its name implies: it controls other devices on the bus. A talker sends data, while a listener

receives data. Depending on the instrument, a particular device may be a talker only, a listener only, or both a talker and a listener.

Any given system can have only one controller (control may be passed to an appropriate device through a special com-

mand), but any number of talkers or listeners may be present up to the hardware constraints of the bus. Generally, the bus is limited to 15 devices, but this number may be

reduced if higher than normal data transfer rates are

required or if longer than normal cables are used.

Several devices may be commanded to listen at once, but only one device may be a talker at any given time. Otherwise, communications would be scrambled much like an individual’s trying to pick out a single conversation out of a large crowd.

Before a device can talk or listen, it must be appropriately addressed. Devices are selected on the basis of their primary

address; the addressed device is sent a talk or listen com-

mand derived from its primary address. Normally, each device on the bus has a unique primary address so that each may be addressed individually.

Once the device is addressed to talk or listen, appropriate

bus transactions are set to take place. For example, if an instrument is addressed to talk, it will usually place its data on the bus one byte at a time. The listening device will then

read this information, and the appropriate software can then

be used to channel the information to the desired location.

2.3 IEEE-488 BUS LINES

The signal lines on the IEEE-488 bus are grouped into three general categories. The data lines handle bus information, while the handshake and bus management lines ensure that proper data transfer and bus operation takes place. Each of the bus lines is active low so that approximately zero volts is a logic one. The following paragraphs describe the purpose of these lines, which are shown in Figure 2-l.

2.3.1 Bus Management Lines

The bus management group is made up of five signal-lines that help ensure an orderly transfer of data. These lines are

used to send the uniline commands described in paragraph

2.4.

1. ATN (Attention)-The ATN line is one of the more important management lines. The state of the ATN line determines whether controller information on the data bus is to be considered data or a multiline command as described in paragraph 2.4.

2. IFC (Interface Clear)-Setting the IFC line true (low) causes the bus to go to a known state by sending the IFC command.

3. REN (Remote Enable)-Setting the REN line low sends the REN command. This sets up instruments on the bus for remote operation.

4. EOI (End Or Identify)-The EOI line is used to send the EOI command that usually terminates a multi-byte transfer sequence.

5. SRQ (Service Request)-The SRQ line is set low by a device when it requires service from the controller.

2-1

TALK.LISTEN.

AN0 dt5NTR0~

(COMPUTER) E

DEVICE 2 ABLE TO

TALK AND E

DEVICE 3

DEVICE 4

ONLY AELti

TO TALK

TO OTHER DEVICES

The complete handshake sequence for one data byte is shown in Figure 2-2. Once data is on the bus, the source checks to see that NRFD is high, indicating that all devices on the bus are ready for data. At the same time NDAC should be low from the previous byte transfer. If these conditions are not met, the source must then wait until the

NRFD and NDAC lines have the correct status. If the source

is a controller, NRFD and NDAC must remain stable for at

DATA BUS

)

least 100ns after ATN is set low. Because of the possibility of bus hang up, some controllers have time-out routines to display error messages if the handshake sequence stops for any reason.

lllll

Once the NRFD and NDAC lines are properly set, the source sets the DAV line low, indicating that data on the bus is now

DATA BYTE TRANSFER CONTROL

valid. The NRFD line then goes low; the NDAC line goes

high once all devices on the bus have accepted the data. Each device will release the NDAC line at its own rate, but the NDAC line will not go high until the slowest device has

accepted the data byte. After the NDAC line goes high, the source then sets the

GENERAL INTERFACE MANAGEMENT

DAV line high to indicate that the data on the bus is no longer valid. At this point, the NDAC line returns to its low state. Finally, the NFRD line is released by each of the devices at their own rates, until the NFRD line finally goes high when the slowest device is ready, and the bus is 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 as described in paragraph 2.4.

1 =E) BUS MANAGEMENT I

EOI 1

1.220/230

Figure 2-1. IEEE Bus Configuration

2.3.2 Handshake Lines

The bus uses three handshake lines that operate in an interlocked sequence. This method ensures reliable data transfer

regardless of the transfer rate. Generally, data transfer will occur at a rate determined by the slowest active device on the bus.

One of the handshake lines is controlled by the data source, while the remaining two lines are controlled by accepting devices. The three bus handshake lines are:

1. DAV (Data Valid)-The source controls the state of the DAV line.

2. NRFD (Not Ready For Data)-The acceptor controls the state of the NRFD line.

3. NDAC (Not Data Accepted)-The acceptor also controls the NDAC line.

2.3.3 Data Lines

The IEEE-488 bus uses the eight data lines that allow data to

be transmitted and received in a bit-parallel, byte-serial manner. These eight lines use the convention DIOI through D108 instead of the more common DO through D7 binary

terminology, The data lines are bidirectional and, as with the

remaining bus signal lines, low is true.

OAV

NRFO

NoAC

VALID

I I

/ ’ j/j ’ ACCEPTOR

DATA DATA

TRANSFER

BEGIN

---

I I

TRANSFER

END

SOURCE

ACCEPTOR

2.210~233

Figure 2-2. IEEE Handshake Sequence

2-2

2.4 BUS COMMANDS

While the hardware aspects of bus is essential, the interface would be essentially worthless without appropriate com-

mands to control communications between the various

instruments on the bus. This section briefly describes the purpose of the bus commands, which are grouped into the following three general catagories:

1. Uniline commands: Sent by setting the associated bus line low.

2. Multiline commands: General bus commands which are sent over the data lines with the ATN line low.

3. Device-dependent commands: Special commands that

depend on device configuration; sent over the data lines with ATN high.

These commands are summarized in Table 2-l.

2.4.1 Uniline Commands

Uniline commands are sent by setting the associated bus

line low. The ATN, IFC, and REN commands are asserted only by the system controller. The SRQ command is sent by an external device. The EOI command may be sent by either the controller or an’external device depending on the direction of data transfer. The following is a brief description of each command.

1. REN (Remote Enable)-When the controller sends the REN command,the instrument will be set up for remote

operation. Generally, the REN command should be sent before attempting to program instruments over the bus.

2. EOI (End Or Identify)-The EOI command is used to positively identify the last byte in a multi-byte transfer sequence. This allows variable length data words to be transmitted easily.

3. IFC (Interface Clear)-The IFC command is sent to clear the bus and set devices to a known state. Although device configurations differ, the IFC command usually places instruments in the talk and listen idle states.

4. ATN (Attention)-The controller sends ATN while transmitting addresses or multiline commands. Devicedependent commands are sent with the ATN line high (false).

5. SRQ (Service Request)-The SRQ command is asserted by an external device when it requires service from the controller. If more than one device is present, a serial polling sequence, as described in Section 4, must be used to determine which device has requested service.

2.4.2 Universal Commands

Universal commands are multiline commands that require no addressing. All instrumentation equipped to implement

the command will do so simultaneously when the command

is transmitted over the bus. As with all multiline commands, the universal commands are sent over the data lines with ATN low.

1. LLO (Local Lockout)-The LLO command is used to lock out front panel controls on devices so equipped.

2. DCL (Device Clear)-After a DCL is sent, instrumentation equipped to implement the command will revert to a known state. Usually, instruments return to their powerup conditions.

3. SPE (Serial Poll Enable)-The SPE command is the first

step in the serial polling sequence, which is used to determine which instrument has requested service with the SRQ command.

4. SPD (Serial Poll Disable)-The SPD command is sent by

the controller to remove all instrumentation on the bus from the serial poll mode.

2.4.3 Addressed Commands

Addressed commands are multiline commands that must be preceded by a listen command derived from the device’s primary address before the instrument will respond. Only the addressed device will respond to each of these commands:

1. SDC (Selective Device Clear)-The SDC command performs essentially the same function as the DCL command except that only the addressed device will respond. Instruments usually return to their default conditions

when the SDC command is sent.

2. GTL(Go To Local)-The GTL command is used to remove instruments from the remote mode of operation. Also, front panel control operation will usually be restored if the LLO command was previously sent.

3. 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.

2.4.4 Unaddressed Commands

The two unaddressed commands are used by the controller to remove all talkers and listeners from the bus simultaneously. ATN is low when these multiline commands are asserted.

1. UNL (Unlistenj-All listeners are removed from the bus at once when the UNL command is placed on the bus.

2. UNT (Untalkj-The controller sends the UNT command to clear the bus of any talkers.

2.4.5 Device-Dependent Commands

The meaning of the device-dependent commands is determined by instrument configuration. Generally, these commands are sent as one or more ASCII characters that tell the device to perform a specific function. For example, FO is sent to the Model 220 or 230 to place the instrument in the standby mode. For complete information on using these commands with the Model 220 or 230, refer to Section 4. The IEEE-488 bus treats device-dependent commands as data in that ATN is high (false) when the commands are transmitted.

2-3

Table 2-1. IEEE488 Bus Command Summary

Command Tvoe Jniline

Aultiline

Universal

Addressed

Unaddress

Device-dependent**

- _ -- .

‘t Some devices respond to GET without addressing. *X = Don’t Care

**See Section 4 for complete description.

2.5 COMMAND CODES

Each multiline command is given a unique code that is

transmitted over the bus as 7-bit ASCII data. This section

briefly explains the code groups which are summarized in Figure 2-3. Every command is sent with ATN low.

1. Addressed Command Group (ACGI-Addressed commands are listed in column ,0(B) in Figure 2-3. Column O(A) lists the corresponding ASCII codes.

2. Universal Command Group WCGI-Columns l(A) and 1 (BI list the Universal commands and the corresponding

ASCII codes.

3. Listen Address Group (LAGKolumns 2(A) and 3(A) list

the ASCII codes corresponding to the primary addresses listed in columns 2(B) and 3(B). For example, if the primary address of the instrument is set to 12, the LAG byte will correspond to an ASCII comma.

4. Talk Address Group (TAG)-TAG primary address values

and the corresponding ASCII characters are listed in columns 4(A) through 5(B).

The preceding address groups are combined together to form the Primary Command Group (PCG). The bus also has another group of commands, called the Secondary Com-

mand Group (SCG). These are listed in Figure 2-3 for informational purposes only; the Models 220 and 230 do not respond to these commands, but other devices may have

secondary addressing capability.

Commands are normally transmitted with the 7-bit code listed in Figure 2-3. For most devices, the condition of 07 (Dl08) is unimpor-

1 Command

REN (Remote Enable) EOI

IFC (Interface Clear) ATN (Attention) SRQ (Service Request)

LLO (Local Lockout) DCL (Device Clear) SPE’ (Serial Poll Enable) SPD (Serial Poll Disable) SDC (Selective Device Clear) GTL (Go to Local) GET (Group Execute TriggerIt UNL KInlisten) UNT (Untalk)

NOTE

1 State of ATN Line

X X X

Low

tant, as shown by the “Don’t Care” indication in the table. Some devices, however, may require that 07 assumes a specific logic state before the commands are recognized.

Hexadecimal and decimal values for each of the commands or command groups are listed in Table 2-2. Each value in the table assumes that D7 is set to 0.

Table 2-2. Hexadecimal and Decimal Command Codes

Command

GTL

SDC

GET

LLO DCL SPE

SPD

LAG

TAG

UNL UNT

*Values shown with D, = 0.

2.6 COMMAND SEQUENCES

The proper command sequence must be sent by the con-

troller before an instrument will respond as intended. The universal commands, such as LLO and DCL, require only that ATN be set low before the command is sent. Other

commands require that the device be addressed to listen first. This section briefly describes the bus sequence for several types of commands.

Comments Set up for remote operation.

Sent by setting EOI low. Clears Interface Defines data bus contents.

Controlled bv external device.

/Locks out front panel controls. ‘Returns device to default conditions.

Enables serial polling. Disables serial polling. Returns unit to default conditions.

Returns to local control. Triggers device. Removes all listeners from bus.

Removes any talkers from bus. Programs Model 220 or 230 for various

modes.

Hex Value*

01 04 08

11 14 18

19 20-3F 40-5F

3F 5F

Decimal Value

1 4 8

17 20 24 25

32-63 64-95

63 95

a”

2-5

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