Keithley 776 Service manual

Model 776 Programmable Counter/Timer

Instruction Manual

A GREATER MEASURE OF CONFIDENCE

W ARRANTY

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.

LIMIT A TION OF W ARRANTY

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. • 28775 Aurora Road • Cleveland, OH 44139 • 440-248-0400 • Fax: [phone] • http://www.keithle y.com

BELGIUM: Keithley Instruments B.V.
CHINA: Keithley Instruments China Y uan Chen Xin Building, Room 705 • 12 Yumin Road, Dew ai, Madian • Beijing 100029 • 8610-62022886 • Fax: [phone]
FRANCE: Keithley Instruments Sarl 3, allée des Garays • 91127 Palaiseau Cedex • 01-64 53 20 20 • Fax: [phone]
GERMANY: Keithley Instruments GmbH Landsberger Strasse 65 • 82110 Germering • 089/84 93 07-40 • Fax: [phone]
GREAT BRITAIN: Keithley Instruments Ltd
INDIA: Keithley Instruments GmbH Flat 2B, WILOCRISSA • 14, Rest House Crescent • Bangalore 560 001 • 91-80-509-1320/21 • Fax: [phone]
ITALY: Keithley Instruments s.r.l. Viale S. Gimignano, 38 • 20146 Milano • 02-48 39 16 01 • Fax: [phone]
NETHERLANDS: Keithley Instruments B.V. Postbus 559 • 4200 AN Gorinchem • 0183-635333 • Fax: [phone]
SWITZERLAND: Keithley Instruments SA Kriesbachstrasse 4 • 8600 Dübendorf • 01-821 94 44 • Fax: [phone]
TAIWAN: Keithley Instruments Taiwan 1 Fl. 85 Po Ai Street • Hsinchu, Taiwan, R.O.C. • 886-3572-9077 • Fax: [phone]

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

The Minster • 58 Portman Road • Reading, Berkshire RG30 1EA • 0118-9 57 56 66 • Fax: [phone]

9/00

Model 776 Programmable Counter/T imer

Instruction Manual

Serial Prefix T74

©1993, Keithley Instruments, Inc.

All rights reserved.

Cleveland, Ohio, U.S.A.

Fifth Printing, April 2001

Document Number: 776-901-01 Rev. E

Manual Print History

The print history shown below lists the printing dates of all Revisions and Addenda created for this manual. The
Revision Level letter increases alphabetically as the manual undergoes subsequent updates. Addenda, which are
released between Revisions, contain important change information that the user should incorporate immediately into
the manual. Addenda are numbered sequentially. When a new Revision is created, all Addenda associated with the
previous Revision of the manual are incorporated into the new Revision of the manual. Each new Revision includes
a revised copy of this print history page.

Addendum D (Document Number 776-901-02) ............................................ January 1999

Revision E (Document Number 776-901-01)...................................................... April 2001

All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc.
Other brand and product names are trademarks or registered trademarks of their respective holders.

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.

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. The user should 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.

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

Users of this product must be protected from electric shock at all
times. The responsible body must ensure that users are 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 be trained to protect themselves
from the risk of electric shock. If the circuit is capable of operating
at or above 1000 volts,

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.

A good safety practice is to expect

no conductive part of the circuit may be

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. Alw ays read the associated infor ­mation 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.

2/01

Table of Contents

1

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

2

2-1
2-2 Performance Checks..
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
2-11

General Information

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

Instrument and Manual Identification ...................................................................................................... 1-I

Configuration.. .............................................................................................................................................

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

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

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

Inspection .....................................................................................................................................................

Specifications ..............................................................................................................................................

installation

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

Power Requirements..

Grounding Requirements.. .....................................................................................................................

Installation and Mounting ..........................................................................................................................

Bench Mounting ..........................................................................................................................................

Rack Mounting.. ..........................................................................................................................................

Portable Use.. ...............................................................................................................................................

Short Term Storage.. ...................................................................................................................................

Long Term Storage or Re-packaging For Shipment ..............................................................................

Safety ............................................................................................................................................................

I-1
l-2

l-2
I -2
I-2
l-2
1-Y

2-1

.............................................................................................................................. ...2-I

.............................................................................................................................. ...2-I

.,.,2-I

2-2

2-2

2-2

2-2

2-2

2-2

2-3

3

3-l
3-2
3-2-l

Operation

Introduction

Front Panel Famlllanzatlon ...........................................................................................................................

Controls ....................................................................................................................................................

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

1-l

3-l

3-1

3-2-2

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

3-2-3
3-3
3-3-l
3-4
3-5
3-6
3-6-l
3-6-2
3-7
3-8
3-9
3-10
3-11
3-12
3-13
3-14
3-14-1
3-14-2
3-14-2
3-15
3-16
3-17
3-18
3-19
3-20
3-20-l
3-20-2
3-2 1
3-22

Connectors ............................................................................................................................................... 3-2

Display And Indicators .......................................................................................................................... 3-2

Rear Panel Familiarization.. ......................................................................................................................

Connectors and Terminals .....................................................................................................................

Power-up Procedure ...................................................................................................................................

Software Reset ............................................................................................................................................ 3-4

Display Messages .......................................................................................................................................

IEEE-488 Error Messages..

Error Indtcatmn

Control Selection ........................................................................................................................................

Selecting a Function ................................................................................................................................... 3-6

Selecting Gate and Delay Time

Setting Trigger Levels.. .............................................................................................................................. 3-8

Setting Input
Selecting The Number Of Displayed Digits..

Selecting Measurement Rate ..................................................................................................................... 3-10

Arming .......................................................................................................................................................... 3-l 1

Continuous Arming With the Input Signal..

Front Panel Arming ................................................................................................................................ 3-l 1

External Arming.. .................................................................................................................................... 3-l 1

Using Auto Trigger Level .......................................................................................................................... 3-12

Using V Peak A.. ......................................................................................................................................... 3-12

Using User Gate.. ........................................................................................................................................ 3-12

Using Delay ................................................................................................................................................. 3-13

Using User Delay ........................................................................................................................................ 3-13

Using Front Panel Set-ups .........................................................................................................................

Store Set-ups.. .......................................................................................................................................... 3-14

Recall Set-ups.. ........................................................................................................................................ 3-14

Using The External Reference. ................................................................................................................. 3-14

Changing The GPIB Address

Condition Controls .............................................................................................................

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

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

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

.................................................................................................................... 3-14

3-3
3-3
3-3

3-4
:;i

3-5

3-8

3-9
3-10

3-l 1

3-14

4

4-l Introduction .................................................................................................................................................

4-2 Bus Desdription ...........................................................................................................................................

4-3

4-3-l Bus Management Lines ..........................................................................................................................

4-3-z Handshake Lines .....................................................................................................................................

4-3-3 Data Lines ................................................................................................................................................

4-4
4-5
4-6 Hardware Considerations..
4-6-l

4-6-2 Connections ............................................................................................................................................. J-5

4-7

4-8 Bus Commands ............................................................................................................................................

4-8-l
4-S-2

4-8-3 Addressed Commands ............................................................................................................................

4-8-4
4-8-5
4-9 Device-Dependent Command Programming

4-9-l Function (F) .............................................................................................................................................

IEEE-488 Programming

4-l
4-I

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

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

Software Considerations.

Typical Controlled System ....................................................................................................................

Changing GPIB Address ............................................................................................................................

Uniline Commands

Universal Multiline Commands

Unaddress Commands ............................................................................................................................

Device Dependent Commands

........................................................................................................................... 4-4

........................................................................................................................ .-I-4

.............................................................................................................................. ...4-G

........................................................................................................... .4-7

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

_.

....

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

4.2
4-2

4-2
4-3

4-4

4-5

4-5
4-6

4-7

4-9

.4-9

4-9
4-9

4-9-2
4-9-3
4-9-4
4-9-5
4-9-6
4-9-l
4-9-8

4-9-9
4-9-10
4-9-l 1
4-9-12
4-9-13
4-9-14
4-9-15
4-9-16
4-9-17
4-9-18
4-9-19
4-10
4-10-l
4-10-2
4-10-3
4-11
4-11-1
4-11-2

Channels A. B Coupling (AC. BC)
Channels A_ B Attenuator (AA, BA)
Channels A. B Filter (AF. BF)
Channels A: B Slope (AS. BS).
Channels A. B Impedance (AI. BI)

Channels A; B Trigger Level
Channels A, B Auto Trigger Level (L)

Gate Time (G, GLJ) ..................................................................................................................................

Delay Time (W, WU) .........................................................

V Peak Measurement Rate (V)

Totalize Mode (M) ..................................................................................................................................

Ratio Mode (C) ........................................................................................................................................

Displayed Digits (N) ...............................................................................................................................

Set-ups (ST. RE). .....................................................................................................................................

Triggering (T) ..........................................................................................................................................

Rate (S). ....................................................................................................................................................

Display Modes (D). .................................................................................................................................

SRQ Mode (Q) and Serial Poll

Reading From Model 776 ..........................................................................................................................

Data Control Commands (R)
Terminator

Prefix (X) ..................................................................................................................................................

Front Panel Error Messages ......................................................................................................................

ILL INS (Illegal Instruction).
ILL PAR (Illegal Parameter)

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

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

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

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

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

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

(AL.

BL)

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

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

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

.............................................................................................................. 4-13

Status Byte Format.. .........................................................................

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

................................................................................................................ 4-18

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

4-11
4-12
4-12
4-12
4-12

4-12
4-12
4-12
4-12

4-13
4-13
4-13
4-13
4-l 3

4-13
4-14
4-14
4-15
4-15
4-l 6
4-17
4-l 8

4-18

5

5-l
5-2
5-3

5-4
5-5
5-6
5-7
5-8
5-9
5-9-l
5-9-2
5-9-3
5-10
5-10-l
5-10-2
5-10-3
S-10-4
5- 10-5
5-10-6
5-10-7
5-10-S
5-10-9
5-10-10
5-10-l 1
S-10-12

Maintenance and Performance Checks

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

Line Voltage Selection ...............................................................................................................................

Fuse Replacement .......................................................................................................................................

Selecting an External Reference

Disassembly Instructions ...........................................................................................................................

Special Handling Of Static Sensitive Devices

Cleaning .......................................................................................................................................................

Repair and Replacement ............................................................................................................................

Performance Checks ...................................................................................................................................

Environmental Conditions .....................................................................................................................

Warm-up Period. ......................................................................................................................................

Recommended Test Equipment..

Performance Checks Procedure

Channels A and B Sensitivity Check
Channel C sensitivity Check
Period A. Period A Averaged Operation Check
Ratio A/B Operation

Ratio C/B Operation ...............................................................................................................................

Pulse A, T.1 A to B and Averaged Operation Check..

Phase A to B Operation Check ..............................................................................................................

Totalize B Operation Check
Auto Trigger Level A and B Operation Check

Delay Operation Check ..........................................................................................................................

User Gate Operation Check
Time Base Accuracy Check..

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

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

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

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

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

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

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

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

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

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

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

................................................................................................................... 5-l 1

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

5-l
5-1
5-1

5-2
5-3

5-3
5-3

5-4
5-4

5-4
5-4
5-4

5-4
5-4
5-5
5-5
5-6
5-7
5-7
5-9
5-9

5-9

5-10

5-l 1

6

6-l
6-2
6-3
6-3-l
6-3-2
6-3-3
6-3-4
6-3-5
6-367
6-4
6-4-l
6-4-2
6-4-3
6-4-4
6-4-S

Theory of Operation

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

Overall Functional Description
Analog Circuitry

Input Circuits A and
Input Circuit C (option 2.4Ci).

10 MHz Standard Reference Oscillator
Reference Oscillator Circuit and TCXO (option 2.4G).
Measurement Logic Section

Power supply ...........................................................................................................................................

Digital Circuitry ..........................................................................................................................................

CPU Block Diagram

Memory Mapping ....................................................................................................................................

Address Decoding
KeyboardDisplay Interface

IEEE Interface .........................................................................................................................................

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

B

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

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

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

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

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

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

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

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

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

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

6-1
6-l
6-5
6-S
6-S
6-6
6-6
6-13
6-14
6-14
6-14
6-14
6-14
6-14
6-14

7

7-l
7-2
7-2-l
7-2-2
l-2-3

l-2-4
7-3
7-3-l

l-3-2

7-3-3

7-3-4

l-3-5

l-3-6

7-3-7

7-3-8

l-3-9

7-4

7-4-l

7-5

7-S-l

7-5-2

7-s-3

7-s-4

7-s-s

7-S-6

7-s-7

Adjustments and Troubleshooting

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

Adjustments

Environmental Conditions.

Warm-up Period .......................................................................................................................................

Recommended Test Equipment
Adjustment Procedures

Adjustment Procedure ................................................................................................................................

Power Supply Adjustment
Trigger Level A Adjustment
Trigger Level B Adjustment
Trigger Level A Offset Adjustment
Trigger Level B Offset Adjustment

Input A xl0 High Frequency Adjustment

Input

Standard - S PPM Time Base Adjustment

TCXO.Time Base Adjustment (option 2.4G)

Troubleshooting

Recommended Test Equipment

Troubleshooting Procedure

Power Supply Checks
Digital Circuitry and Display Checks..
Standard S PPM Reference Oscillator Checks..
SO0 MHz Reference Oscillator and TCXO Checks
Trigger Level Checks
Signal Conditioning and Input Circuit Checks..
Measurement Logic

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

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

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

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

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

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

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

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

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

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

B xl0 High Frequency Adjustment

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

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

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

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

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

Section Checks

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

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

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

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

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

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

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

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

7-l
7-l
7-l
7-l
7-l
7-l
7-3
7-3
7-3

7-3
7-3
7-3
7-3

7-4
7-4
7-4

7-4
7-4

7-S
7-S

7-6
7-6
7-6
7-6
7-6
7-6

6

8-l

8-2 Ordering Information

8-3 Parts Description.. .......................................................................................................................................

Parts List

General .........................................................................................................................................................

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

8-l
8-1
8-1

General Information

l-l. Introduction

This manual provides operating and maintenance infor-

matron

Counter/Timer. Section 1 is a general description of the

instrument. Section 2 and 3 obtain installation and op­erating instructions. IEEE programming is explained in
Section 4. Maintenance and performance checks are
provided in Section 5. The theoF of operation is de­scribed in Section 6. Section 7 oullines calibration and
troubleshooting procedures. Section 8 contains tables of
replaceable parts. Section 9 contains schematic and
component location diagrams.

Model 776 is a Fen digit microprocessor based fully­programmable. three-channel Universal Counrcr I
Timer. The instrument mcasurcs with a vev high reso­lution and precision the following paramctcrs: Frc­quency A. Frequency B. Frequency C. Period A. Pulse­width. Time interval A to B. Total counts B. Ratio A/B.
Ratio C/B. Phase A to B and Amplitude peaks. An
averaging function is available for improved resolution
in time measurement: resohes intervals of pica sec­onds. Various repetitive tests. no matter how complex.
are greatly simplified b>~ utiliziog any of the IO pre-pro­grammed front panel set-up. Set-ups are stored in a
non-volatile memory and can be recalled by a simple
ke.s stroke.

for

the

Model

716

Programmable

as low as 0.01 Hz to more than 225 MHz. The reciprocal
technique is being used in low frequency mcasurcmcnts.
up to exactly 120 MHz. where the measurement tcch­nique is changed to conventional measurement tcch­nique. Model 776 measures frcqucncies of input signals

with minimum resolution of nine digits in one second
of gate time. With the TCXO
776l2.46. the displayed result in largely enhanced. both
in terms of stability and accuracy.

In Model 776. the lraditionally featured decade

steps of gale times. are replaced by a more flerible
variable gate time. This feature permits a choice from
500 internally pre-selected gate interwls. or an! ester­nal gate intcnal which is applied to a rear panel BNC
conneclor. Internal gate times range from 100 ps to IO
s. External gate expands this range to 1000 s. Trigger
leveI my be selected maounll~~ or left to bc aulomali­call? adjusted. by the instrument. to the optimum level.
thus eliminating false lriggcring on unknown signals.

NOTE

This manual provides a complclc dc­scription of all fcrturcs of the 776
Series. Therefore. several of the fea­tures that are described in the follow­ing paragraphs may not be installed
in your instrument.

time

base of the Model

Model 776 utilizes a combination of two measure­ment techniques in order to always achieve maximum
display resolution. Some functions. such as Frequent!
measurement function. can be displayed with up to ten
digits. Such resolution can be gained from frequencies

1-2. Instrument Identification

These KeithIcy’ instmmcnts are identified by a serial

number. which is located on lhe rear panel. The lvo
most significant digits (Txs) identify instrumcnl modi-

I-I

•

•

•

General Information

fication. If this prefix differs from that listed on the title
page of this manual, there are differences between this
manual and your instrument.

1-3. Configuration

There are two configurations available for the Model 776:

Model 776 - Two-channel 225 MHz programmable
counter/timer.

Model 776/2.4G - Same as above with 2.4 GHz Chan­nel C and TCXO time base.

Model 776/2.4G/R - Same as above with rear panel
inputs.

1-4. Warranty Information

Warranty information is located on the inside front cover
of this instructions manual. Should your Model 776
require warranty service, contact the Keithley representa­tive or authorized repair facility in your area for further
information. When returning the instrument for repair, be
sure to fill out and include the service form at the back of
this manual to provide the repair facility with the neces­sary information.

1-5. Manual Addenda

Any improvements or changes concerning the instrument
or manual will be explained in an addendum included with
the manual. Be sure to note these changes and incorporate
them into this manual.

1-6. Safety Symbols And Terms

The following symbols and terms may be found on an
instrument or used in this manual.

!

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

The WARNING heading used in this 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 used in this manual explains
hazards that could damage the instrument. Such damage
may invalidate the warranty.

1-7. Inspection

The Model 776 was carefully inspected, both electrically
and mechanically before shipment. After unpacking all
items from the shipping carton, check for any obvious
signs of physical damage that may have occurred during
transit. (Note: There may be a protective film over the
display lens, which can be removed.) Report any damage
to the shipping agent immediately. Save the original
packing carton for possible future re-shipment. The
following items are included with every Model 776 order:

Table 1-1. Model 776 Specifications

INPUT CHARACTERISTICS

(Channel A & B)
RANGE

DC coupled
AC coupled 1 M Ω
50 Ω

SENSITIVITY (X1)

0 to 200 MHz
200 MHz to 225 MHz
5 ns Minimum Pulse Width

SIGNAL OPERATING RANGE

(X1)
(X10)

DYNAMIC RANGE (x1)

0 to 100 MHz
100 MHz to 225 MHz

Page 1-2

: 0 to 225 MHz.
: 30 Hz to 225 MHz.
: 1 MHz to 225 MHz.

: 50 mV rms sine wave.
: 75 mV rms sine wave.
: 75 mVp-p.

: -5.00 Vdc to +5.00 Vdc.
: -50.0 Vdc to +50.0 Vdc.

: 75 mV to 5 Vp-p.
: 150 mV to 2.5 Vp-p.

Table l-l.

Model 776 Specificntions (continued)

IMPEDANCE

: 1 MQ or 50 .Q nominal shunted by less than 4.5 pF.

switchable.

LOW PASS FILTER : -3 dB NOMINAL at 100 KHz. switchable.

COUPLING

: AC or DC. switchable.

DAMAGE LEVEL (AC or DC)

(Xl)

: DC to 2 KHz - 200 V (DC + pk AC):

2 KHz to 100 KHz - lsi05 V rms Hz/Freq:
Above 100 KHz - S V rms.

(X10)

: DC to 20 KHz - 200 V (DC + pk AC):

20 KHz to 100 KHz - 4~10~ V rms Hz/Freq:
abo\:e 100 KHz - 50 V rms.

50 R

: 5 v rms

TRIGGER LEVEL CHARACTERISTICS
(Channel A and B)

MANUAL TRIGGER (auto trigger off)

(Xl)
(X10)

: -5.00 Vdc to +5.00 Vdc:
: -50.0 Vdc to i50.0 Vdc.

Setting Accuracy : Xl. * (35 mV +2% of reading): X10, + (350 mV +2% of

reading).
Resolution (X 1) : 10 mV: (X10): 100 tnV.
Preset (Xl) : 0.00 Vdc: (X10) 00.0 Vdc.
Trigger Slope

: Independent selection of positive or negative slope. switchable

AUTO TRIGGER
Frequency Range

DC Coupled : 100 Hz to 150 MHz.
AC Coupled 1 MO : 100 Hz to 150 MHz.
50 n

: 1 MHz to 150 MHz.

Auto Trigger Level Range : 150 vp-p.

Minimum Amplitude : I00 mV rms sine wave. 280 mVp-p.
ATTENUATOR

Manual

: X1 or Xl0 NOMINAL. selectable.

Auto : Attenuator is automalically enabled when in Auto Trigger

Mode.

Auto Attenuator Sensitivity : Attenuator is switched when peak input signal exceeds 5. I
VP-P.

NOTES:

1. Auto trigger is disabled in the following functions: Totalize B and Frequency C.

2. Auto trigger function requires that a repetitive signal be present at the input connector.
FREQUENCY A & FREQUENCY B

Measurement Technique : Reciprocal. below I20 MHz and in User Gate. and in Hold

operating modes: Conventional, above I20 MHz.

Measurement technique is automatically selected by the

instrument.

Range : 0.01 Hz to 225 MHz.

1-3

General Information

Table l-l.

Model 776 Specifications (continued)

LSD(‘) Displayed

Reciprocal

Conventional

Resolution
Accuracy
FREQUENCY C

(available with Model 776/2.46)
Range

Input Impedance
Sensitivity
Dynamic Range
VSWR

Dama e Level

7

LSD(’ Displayed
Resolution

Accuracy

4

ns s freaw

gate time.

e.g min 9 digits in one second of
gate time.
l/gate time.

* LSD * (1.4 x Trig errorc2) s Frequency)

gate time

i resolution i Time Base error’3’ s Frequent)

50 MHz to 2.4 GHz.
SO .f2. AC coupled.

15 mV to 2.4 GHz.

15

mV rms to 4 V rms.
<2:1 (typically l.S:l).
AC. 5 V rms: DC. f40 V.
Same as for Frequency A & B.
Same as for Frequency A & B.
Same as for Frequency A & B.

PERIOD A, PULSE A, TIME INTERVAL A to B
Range:

LSD(‘)

Period A. Pulse A
Time Interval A to B

Displayed

Below 20 s
Above 20 s

5 ns to 2000 s.

0 ns

to

1 ns:

5 s Time s 10.” s.

Resolution

Below 20 s
Above 20 s

Accuracy

+2 LSD + start trigger error@) i stop trigger error?
; LSD.

f (Time Base errorc3)
f 1 ns * resolution.

Time Delay

Active only with Time Measurements - single. First input
transition opens the gate. Delay inhibits the consequent
transitions.

Internal

500 internal pre-programmed delay intervals can be inserted
between START and STOP of Time Interval A to B. Inputs

during delay are ignored.
Internal Range
Preset Position

External

100 ps to 100 s.

1 s.
User selectable delay intervals can be applied through rear
panel BNC connector.

External Range

100 ps

to

2000 s.

2000 s.

1 Time) i Trig level timing error

(4)

Page l-4

General Information

Table l-l.

Model 776 Specijjcotions (continued)

TIME MEASUREMENTS AVERAGED
PERIOD A AVERAGED
&!?‘) Displayed

Resolution
Accuracy

Number of Periods Averaged

PULSE A, TIME INTERVAL
Range

Pulse A
Time Interval A to B

LSD(‘) Displayed
Resolution
Accuracy

Dead Time Stop to Start
Number of Samples Averaged

: 8 ns to 10 s
: 4 ns s Period.

gate time

: f LSD * il.4 s Trig error(‘) s Period)

It resolution + (Time Base errorc3) s Period).

A to B AVERAGED

5 ns to 10 s

-3 ns to 10 s (A and B signals must have the same
repetition rate).

4 ns/ J
3~ (1 LSD + 10 ps).
+ (Time Base Error”) x Time) zt 1 ns i!resoiution
+ Trigger Level Timing Errorc4) f (Trigger error) / fi

20 ns minimum.
N = gate time s Frequency.

e.g miu 9 digits in 1 second of gate time.

eate time

PHASE A to B AVERAGED
Range

example

Frequency Range
LSD(‘) Displayed

Resolution
Accuracy

Number of Cycles Averaged
Minimum Amplitude

TOTALIZE B
Frequency Range
Totalizing Range
Gate Modes

Infinite
Gated by A

Gated by AA

Gating Transition
Dead Time Stop to Sta#)

0 to 360” s (1 - 20 ns s Frequency A).
0 to 359.99O at 1 KHz: 0 to 180.0’ at 25 MHz.

0.1 Hz to 25 MHz. A and B signals must have the same
frequency.

4 ns s 360’ s (1 +fi)

gate time

or 0.01”. whichever is greater.
+ 1 LSD.
k resolution f (1 ns s Frequency A s 360’) *
It Trigger Level Timing
+ (Trigger error

(2) s Frequency A s 36OO)

(4) s FrequencyA x 360”) ?

Error

\iN

N = gate time s Frequency A.

100 mV rms sine wave.

0 tn 120 MHz.
0 to lOI - 1.

Totalizing on B indefinitely.
Totalizing on B between a pair of two consecutive
transitions of the opposite direction on A.
Totalizing on B between a pair of two consecutive
transitions of the same direction on A.
Positive or Negative transitions. selectable.
20 ns min from stop transition to the nest start transition.

1-5

General Information

Table l-l.

Model

LSD displayed
Resolution

Accuracy

Infinite
Gated by A, Gated by AA

RATIO AIB
Frequency Range

A

B

LSD(‘) displayed
Resolution

Accuracy
RATIO C/B

Frequency Range

C
B

LSD(‘) displayed
Resolution and Accuracy

776

Specifications (continued)

: 1

count

of channel B input signal.

: 1 LSD.

: Same as LSD.
: * pulse repetition rate B x Trigger error(2) A

total counts B

: 0.01 Hz to 225 MHz:
: 0.01 Hz to 125 MHz.

4 x Ratio--__

Frequency A s gat;z:‘”

: + LSD ,Trieeer B x Ratio

gate time

: Same as resolution.

: SO MHz to 2.4 GHz;
: 10 Hz to 225 MHz.

4 s Ratio

Frequency B s gate time

: k LSD.

V PEAK A
Function

Frequency range

Slow Rate

Fast Rate
Dynamic Range
Resolution xl

Accuracy
GATE TIME

Internal Gate Time

Internal Range

Preset Position

External Gate Time

External Range
External Input

External Gate Delay(‘)

: Displays simultaneously. with 3 digits each, the maximum

and minimum peaks of Channel A input signal. Decimal
points and polarity are autotiaticallg displayed.

: 40 Hz to 10 MHz:
: 100 Hz to 10 MHz.
: 280 mV p-p to 51 V p-p.
: 10 mV: x10: 100 mV. Attenuator is activated automalically

if either the positive or the negative peaks of the input
signal exceeds fS.l V or when the peak to peak voltage

exceeds 5.1 V.

: + resolution i O.l(Vpas pli - Vneg & * 35 mV.

: 500 pm-programmed gate time intervals.
: 100 ps to 10 s or one period of the input. which ever is

longer.

: 1 s.
: User selectable gate time intemals. ranging from 100 ps

to 1000 5.

: 100 ps to 2000 s. External gate not available with Time

measurements - single slmt. Totalize B and Phase A to B.

Rear panel BNC connector: accepts TTL level signals.

j cl0 ps.

Page l-6

Table l-l. A,fodel 776

EXTERNAL ARMING (TRIGGER)

Function
I”PUl

Impedance

.Speci@?tions (continued)

Arms the instrument when set to HOLD mode
Via Rear panel BNC.

1 KC2 nominal.

Level

Logic

Minimum Pulse Width

Trigger Delay(‘)
STANDARD TIME BASE

Frequency

Aging Rate
Temperature Stabilit)

Line Voltage

Clock IN/OUT
External Time Base Input
Time Base Out

TCXO TIME BASE

(available with Model 776/2.46)
Frequency
Aging Rate

Temperature Stability
Line Voltage

Clock IN/OUT
External Time Base Input

Time Base Out
GPIB INTERFACE

Programmable Controls
Multiline Commands
Uniline Commands
Interface Functions

Data Output Format Reading
Gate/Delay Time and Trigger Level
Data Output

Single Shot
Normal Mode
Fast Mode

Address Selection
GENERAL

Display Rate

Normal
Hold

Fast

TTL.

Positive true

10 ps.

<SO ps.

10 MHz.
<I s IO-‘/month.
<5 s 10’6 0 to 50 “C.
<I X 10.’ for 10% change (short term).

Selected with an internal switch.

Rear Panel BNC accepts 10 MHz TTL.

10 MHz appros 2 V from a 51 0 source.

10 MHz.

<I s lO~‘/month: <I x 10e6/year.
Cl s 10‘6. 0 to 50 “C.

<I s 10“‘for 10% change (short term).
Selected with an internal switch.
Rear Panel BNC accepts 5 or 10 MHz ‘ITL. Selected via
an internal switch.

10 MHz appros 2 V from a 51 n source.

: All front panel controls except POWER switch.
: DCL. LLO. SDC. GET. GTL. UNT. UNL> SPE. SPD.
: IFC. REN. EOI. SRQ. ATN.
: SHl. AHl. T6. TEO. L4. LEO. SRI, RLI. PPO. DCI. DTI.

CO. El.

: With prefix 18 ASCII characters plus terminator: Without

prefix - 1-t ASCII characters plus terminator.

: With prefix - 9 ASCII characters plus terminator;

Without prefix - 5 ASCII characters plus terminator.
One reading processed after trigger.

Approximately four readings/second. formatted.
Up to 100 reading/second. formatted.
Front panel programming. Address is stored in a
non-volatile memory.

Approximately four measurements per second:

Single shot measurement. taken with each press of RESET:

Up to 100 measuremeals per second.

Table l-1.

Model 776 SpeciJiconons (continued)

Arming
Reset
Trigger Level Outputs

: Each channel is armed by it’s own signal
: Clears display and re-cycles measurement.
: DC Outputs via rear panel terminals. not adjusted for

attenuators.

Accuracy

: DC (Xl) *35 mV * 2% of trigger level reading.

Output Impedance : 1 KQ 1%.

Display

: 10 digits seven segtnents LED. 0.56” high. 2 digits for

exponent.
Displayable Digits : Selectable from 3 to 10 most significant digits.
Gate : LED indicator lights when gate is open.
Stored Set-ups : Ten measurement set-ups. including trig levels, gate/delay

time. input conditioning and measurement rate may be

stored in memory and subsequently recalled. When AC

mains power is removed. a non-volatile memory preserves

the stored set-ups for a typical period of 3 years.
Operating Temperature : 0 to 50 OC ambient. 0 to 80% relative humidity.
Storage Temperature
Power Requirements

: -25 to 65 “C.
: llY230 V rms &lo% (rear panel switch select) 48-60 Hz.

30 W maximum.
Warm-Up : I hour to rated accuracy and stability.
Dimensions
Rack Mount Dimensions
Weight:
Accessories Furnished:

: 3.5” s 8.3” s 15.4” (H s W s D) 89 s 211 s 391 m”m.

: 3.5” s 19” (H s W) 89 x 483 m”m.
approximately 8 lb (3.5 kg).
Power Cord, Operating Manual.

DEFINITION OF TERMS
(1) LSD : Unit value of least significant digit. Calculation should be

rounded as follows 1 to <5 Hz becomes I Hz. 5 ns to

cl0 ns becomes 10 ns etc.

(2) Trigger Error

d(ei*+On*)

Input slew rate at trigger point

Where: ei is the rms noise voltage of the counter‘s input
channel (250 pV typ.) en is the rms noise of the input
signal for 225 MHz band-width.

(3) Time Base Error

: Maximum fractional frequency change in time base

frequency due to all errors: e.g aging. temperature. line

voltage etc.

(4) Trigger Level Timing Error (xl)

:

18mV

_.~~ + ~?rnV

Input slew rate at - Input slew rate at
start trigger point stop trigger point

5) External arming (trigger) delay

: Delay from the positive going slope of the arming signal to

the internal gate open signal.

(6) External gate delay

: Delay from the positive going slope of the gating signal to

the internal gate open signal.

(7) Dead Time

: Minimum time between measurement which the counter is

busy in performing the measurement. The counter will not
at this time respond lo any input transition.

Page l-8

l

Model 776 Programmable CounterfIimer with line
cord.

. Model 776 Instructions Manual.
If an additional manual is required, order:
. Keithley part number 776-901-00.

1-8. Specifications

Instrument specifications are listed in Table I-l. These
specifications are the performance standards or limits
against which the instrument is tested.

General Informnlion

NOTE

All specifications in the following
table apply after a warm-up period of

1 hour and at ambient temperature of

25Y f50C.

1-9

Installation

2-1. Introduction

This section contain information and instructions nec­essary for the installation and shipping of the Model

776. Details are providedforpowerconnection. ground­ing safety requirements. installation information. and
x-packing instructions for storage or shipment.

2-2. Performance Checks

The instrument was carefully inspected for mechanical
and electrical performance before shipment from the
factory. It should be free of physical defects and in
perfect electrical order upon receipt. Check the instru­ment for damage in transit and perform the electrical
procedures outlined in Section 5. If there is indication
of damage or deficiency. see the warranty in this manual
and notify your local Keithley field engineering rep­resentative or the factory

CAUTION

It is recommended that the operator

be fully familiar with the specifica-

tions and all sections of this manual.
Failure to do so may compromise the
warranty and the accuracy which
Keithley has engineered into your in­strument.

2-3. Power Requirements

The instrument may be operated from any one of the
following sources: a. 103.5 to 126.5 Volts (1 IS Volts

nominal) b. 207 to 253 Volts (230 Volts nominal).

The instrument operates over the power mains frc­quency range of 18 to 63 Hr. Always verify that the
operating power mains voltage is the same as that speci­fied on the rear panel voltage selector switch.

CAUTION

Failure to switch the instrument to

match the operating line voltage will
damage the instrument and may void
the warranty.

The instrument should be operated

from a power source with its neutral

at or near ground (earth potential).

The instrument is not intended for

operation from two phases of a

multi-phase ac sqstcm or across the

legs of a single-phase. three-wire ac

power system. Crest factor (ratio of

peak voltage to rms) should be typi-

cally within the range of 1.3 to I.6

at 10% of the nominal rms mains

voltage.

24. Grounding Requirements

To insure the safety of operating personnel. the U.S.
O.S.H.A. (Occupational Safety and Health) rcquire­ment and good engineering practice mandate that the
instrument panel and enclosure be “earth” grounded.
All Keithley instruments are provided with an Uuder­writers Laboratories (U.L. and V.D.E) listed lhrec-con­ductor power cable. which when plugged into an ap­propriate power rcceptaclc. grounds the instrument.

2-l

The long offset pin on the male end of the power cable
carries the ground wire to the long pin of the receptacle
on the rear panel of the instrument.

CAUTION

To avoid operator shock hazard do
not exceed the power mains voltage
frequency rating which limits the
leakage current between case and
powr mains. Never expose the in­strument to rain. excessive moisture,

or condensation.

2-5. Installation And Mounting

tective covering such as a plastic bag or strong krali
paper. Place power cable and other accessories with
the instrument. Store the cowred voltmeter in a clean
dry area that is not subject to extreme temperature vart­a&s or conditions which may cause moisture to con­dense on the instrument.

2-10. Long Term Storage Or

Re-Packing For Shipment

If the instrument is to be stored for a long period or
shipped. proceed as directed below. If you have any
questions ccmtact your local Keilhley field engineering
representative or the Keithlcy Scwice Department at
the factory.

The instrument is fully solid state and dissipates only
a small amonnt of power. No special cooling is required.
However. the instrument should not be operated where
the ambient temperature exceeds 50°C. when the rela­tive humidity exceeds 80% or condensation appears
anywhere on the instrument. Avoid operating the in-

strument close to strong magnetic fields which may
be found near high power equipment such as motors.
pumps. solenoids. or high power cables. Use care when

rack mounting to locate the instrument away from

sources of excessive heat or magnetic fields. Always

leave 1 cm (1.5 inches) of ventilation space on all

sides of the instrument.

2-9. Bench Mounting

The instrument is shipped with plastic feet. tilt stand

in place and ready for use as a bench or portable in-

strument. See outline drawing Figure 2-l for dimen-

smns.

2-7. Rack Mounting

The instrument may be rack mounted in a standard 19

inch EIA rack. The instrument may be rack mounted

in Rack Mount Kit option Rack.

2-9. Portable Use

The instrument may be used in applications requiring

portability. A tilt stand consisting of two retractable

legs is provided with each unit.

2-9. Short Term Storage

If the instrument is to be stored for a short period of

time (less than three months). place cardboard over

the panel and cover the instrument with suitable pro-

If the original Keithley supplied packaging is to

be used proceed as follows:

1. If the original wrappings. packing material. and con­tainer have been saved. *e-pack the instrutnent and ac­cessories originally shipped to you. If the original con­tainer is not wailablc. one may be purchased through
the Keithley Service Department at the factory.

2. Be sure the carton is well sealed with strong tape
or metal straps.

3. Mark the carton with the model number and serial
number with indelible marking. If it is to bc shipped.
show sending address and return address cm two sides
of the box: cover all previous shipping labels.

If the original container is not available. proceed

as follows:

1. Before packing the unit. place all accessories into
a plastic bag and seal the bag.

2. For extended storage or long distance shipping only.
use U.S. govermnent packing method II C and tape a
two-unit bag of desiccant (per MIL-D-3164) on the
rear cover.

3. Place a I3 cm (5 inch) by Xl cm (I2 inch) piece
of sturdy cardboard over the front panel for protection.

4. Place the counter into a plastic bag and seal the
bag.

5. Wrap the bagged instrument and accessories in one
inch thick flexible cellular plastic film cushioning ma­terial (per PPP-C-795) and place in a barrier bag (per
MIL-B-131). Extract the air from bag and heat seal.

6. Place bagged instrument and acccssorics into a 250

mm (10 inch) s 360 mm (I-I inch) s SO8 mm (20 inch)

2-2

Installation

fiber board box (per PPP-B-636 type CF, class WR,
variety SW, grade V3C). Fill additional spaces with
rubberized hair or cellular plastic cushioning material.
Close box in accordance with container specifications.
Seal with sturdy water resistant tape or metal straps.

7. Mark container “DELICATE INSTRUMENT”,
“FRAGILE”, etc. Mark instrument model and serial
number and date of packaging. Affix shipping labels
as required or mark according to MIL-STD-129.

NOTE

If the instrument is to be shipped to
Keithley for calibration OT repair, at­tach a tag to the instrument identi­fying the owner. Note the problem,
the symptoms, and service or repair

desired. Record the mode1 and serial
number of the instrument. Show the
work authorization order as we11 as
the date and method of shipment. AL­WAYS OBTAIN A RETURN
AUTHORIZATION

NUMBER
FROM THE FACTORY BEFORE
SHIPPING THE INSTRUMENT TO
KEITI-ILEY.

2-11. Safety

Be fully acquainted and knowledgeable with al1 aspects
of this instnxtion manual before using the instrument
to assure operator safety and protection against per­sonnel shock hazard.

igure

2-l.

Model 776 - outline dimensions.

2-3

lnstnllation

Notes

2-1

3

Operating Instructions

3-I. introduction

Model 776 operation is divided into two general catego­ries: basic bench operation. and IEEE-488 operation.
Basic bench operation. which is covered in this section.
consists of using the Model 776 to perform basic fre­quency. time. peak voltage. and phase measurements.

IEEE programming can also be used to greatly enhance
the capability of the instrument in applications such as
automatic test equipment. These aspects are covered in
details in Sections 3 and 1.

3-2. Front Panel Familiarization

The front panel layou1 of the Model 776 is shown in

Figure 3-l. The fionl panel is generally divided into

three sections: controls. conneclors. display and indica­tors. The following paragraphs describe the purpose of
each of these items in details.

3-2-l.

All the front panel controls escepc [POWER] are mo-

mcntarv contact switches. Many controls include an
annu&ator light to indicate the selected mode. Con­trols which do not have an annunciator ligh1. when

pressed. will cause an immediate reaction on the dis-

play. The con1roIs arc dbided into func1ional groups for

easier operation. Front panel controls are divided to 1he

following functional groups: Power. Mode. Funclions.

Display Modifiers. and Inpu1 Setting.

1. POWER The [POWER] witch controls the AC

power to the instrument. Pressing and releasing the

Controls

switch once turns the power on. Pressing and rclcasing
the switch a second time turns 1hc power off.

2. MODE. There are two push-buttons in the MODE
section: [CLRLCL] (clear/local). and [ZndlEXEj
(second/execute). The [2nd] push-button is used to se-

lect secondary functions. Normally. the secondary func­tions are marked below the push-buttons. To help dis­tinguish between normal and secondary functions. all
secondary funclions are prin1ed in yellow. Pressing the

[2nd/EXE] push-button will cause the instrunlcnl to
display the following reading:

2nd ?

The reading is blinking indicaling lhat the counlcr is
ready for a conscqucnt press of anolhcr push-bulton
which was assigned a second function. Pressing the

[2nd/EXEj push-button again will res1ore normal op
eration. The [CLR/LCL) push-bulton when pressed.
and the instrument nas in remote operation (bu1 not in

remote lockout condition LLO). restores local opera­tion. When

this push-bulton clears the display and arms the counter

for the next n1casurcn1cn1 cycle.

3. FUNCTION. The 1hree FUNCTION push-buttons
control the 1ype of measurcmcnt. Each push-button is
used IO select one of three functions.

FREQ. - The FREQ push-butlon places the instru­ment in one of three frcqucocy ntcasurcn~cnt functions:
Frequency A. Frequency B or Frequency C. Consccu­tive pressing of the [FREQJ push-butlon uill toggle

the

instrumen1 is in local operation. pressing

3-1

MODE

FUNCTION

between frequency A. Frequency l3 and Frequency C

functions.

TIME - The TIME push-button sets the Model 776

up to measure one of three time

measurement

functions:
Period A. Pulse A or Time Intenxl A to B. Consecutive
pressing of the [TIME] push-button will toggle be-

tween these three functions.

RATIO -The RATIO push-button places the inslm-

ment in one of three ratio measurement functions: To-

talize B (infinite. gated by A. or gated by AA). FRQlB

(C/B or A/B). or Phase A relative to B. Consecutive
pressing of the [RATIO] push-button will toggle be­twcen Totalize B. FRC$B. and Phase A to B functions.

1. DISPLAY/MODIFY. The two DISPLAY/MODIFY
push-buttons modify the display from normal fre­quency. time or ratio reading to another reading such as
trigger level. gate time. totalize mode. V peak mode. or
delay time.

5. INPUTS. There are 5 push-buttons at the INPUTS
section. These buttons select functions which ad.iust
input signal properties before it is applied to the actual
input. Push-buttons control attenuation. coupling.
slope. input impedance. and low pass filter to suppress
high frequency noise.

6. VERNIER. The two push-buttons in the VERN!ER
section are used as a digital potentiometer. The VER­NIER operates in conjunction with the following func­tions: Trigger leyel. Gate time. Dela! time. Digits. Ad­dress. Totalize mode. Vpeak mode. Analog out. and

Offset. The two push-button also set these parameters
to a pm-set position.

7. SET-UPS. There are tn’o push-buttons in the SET­UPS section One is used to slorc a complete front panel
set-up. The other button is used to recall a stored set-up.

3-2-2 Connectors

The connectors arc used to connect the Model 776 to the
unknown signal.

1. CHANNEL A. The CHANNEL A connector is used
\\hen making mcasurcmcnt which arc related to channel A.

2. CHANNEL B. The CHANNEL B connector is used
when making measurements which are associated with
channel B.

3. CHANNEL C. The CHANNEL C connector is used
for high frequency measurements. up lo 2.7 GHz with a

50 fi input impedance. Although this terminal is alva!~s
installed. the internal circuitq to operate this function
is optional and ma: not be installed cm your model.

NOTE

If front panel connectors are present
on a Model 776/2.4G/R unit. they are
not functional.

3-2-3. Display And Indicators

1. DISPLAY. The function of the display is to shou the
result of the processed mcaswcmcnt. The display con-

sists of a 10 digit mantissa and a single digit csponcnt.

3-2

The exponent uses a leading minus to indicate negative
values. The sign on the exponent changes to + for zero
or positive values. The display is also used to indicate
information other than the measurement such as the gate
time or the trigger level.

2. INDICATORS. There are 30 indicators located on
the front panel. The indicators are used to point at a
selected function or signal to the user that the instru­ment is set to a special function like auto trigger or
remote operation.

33 Rear Panel Familiarization

Figure 3-2 shows the rear panel layout of the model 776.

3-3-l. Connectors and Terminals

1. AC RECEPTACLE. Power is applied_ through the
supplied power cord. to the 3-terminal AC receptacle.
Note that the selected power supply voltage is marked
on the rear panel above the line voltage selector switch.

2. LINE SWITCH. The LINE VOLTAGE SELECTOR
switch selects one of the primary voltage which are
marked on both sides of the switch

3. LINE FUSE. The line fuse provides protection for
the AC power line input. For information on replacing
this fuse. refer to Section 5.

4. IEEE-188 CONNECTOR. This conneclor is used
to connect the instrument to the IEEE-488 bus.

5. TRIGGER LEVEL OUTPUTS. Tbesc three lermi­nals are used for monitoring. by an external DMM or

oscilloscope. the DC voltage coming from channels A
and B trigger level circuits.

6.

CLOCK. This BNC connector is used to output tbe
internal clock as a reference to another instrument. The
same input may be connected to an external reference.

The function of this input/output is marked above the
connector.

7. EXTERNAL ARMING/GATE/DELAY. A BNC
connector which may receive one of three signals: arm­ing pulse. external gate signal or external delay pulse.
This input is useful when gate or delay times other then
the internal times are required. or to take one reading
with model 776 in synchronization with other cquip­ment.

8. CHANNEL A, CHANNEL B, CHANNEL C (Not
shown). These connectors. only present on a Model
776/2.4GIR. are used to connect the “nil to the unknown
signal. Iffront panel connectors are present. they are not
functional.

34. Power-Up Procedure

The basic procedure of powering up the Model
described below.

716

is

Figure 3-2.

Rear Panel Cormecrors and Tenninnls.

3-3

operating InstrmYions

1. Connect the female end of the power cord to the AC
mains receptacle on the rear panel. Connect the other
end of the power cord to a grounded AC outlet.

CAUTION

Be sure the power line voltage agrees
with the indicated value on the rear
panel of the instrument. Failure to
heed this warning may result in in­strument damage.

WARNING

The instrument is equipped with a
3-wire power cord designed to be
used with grounded outlets. When the
proper connections are made. the in­strument chassis is connected to the
power line ground. Failure to use a
properly grounded outlet may result
in personal shock hazard.

2. Turn on the power by pressing and releasing the
POWER switch on the front panel.

3. The instrument will then begin operation by perform­ing a display and indicator test which takes approsi­mately one second. All mode and IEEE indicators will
turn on and the display will appear as follows:

4. To verify that all display segments are operating.
compare the instrument’s display with the above during

the test.

7. following the software re\-ision level. the instrument
will display the previously selected IEEE primary ad­dress which is set through front panel programming and
stored in the non-volatile memoty. For example. with
the rear panel witch set to address 25. the display will
show:

IE Adr 25

8. Following these display messages. the instrument
will go into the normal operating mode and begin dis­playing readings. The instrument will bc set to the
previously programmed front panel set-up.

3-5. Software Reset

One. who is not yet fully familiar with the front panel
operation of the Model 776. may find himself locked in
a “dead-end” situation where nothing operates the way
it should. The fastest way to restore the counter lo a
known condition is by resetting the instrument’s soft­ware. This can be done by pressing the [tnd/EXEJ

push-button and then pressing the [DCLl push-button

(second function to the [CLRlLCLl push-button). The
instrument will be then be set to it‘s factory selected

default. Table 3-1 summarizes these defaults.

NOTE

Software reset has no effect on any of
the front panel set-ups which were
previously stored in the mcmoty loca-

tions 0 through 9. The software reset
also has no effect on the programmed
GPIB address.

5. Following the display test. the instrument proceeds
by displaying the options installed. When no option is

installed. the instrument will display the following mes-

sage:

776

If option 2.1G (2.1 GHz C Channel input + TCXO) is
installed. the instrument will display the following rnes­sage:

776-2.16

6.

Once the model number and the installed options are
displayed. the instrument will perform ROM and RAM
tests. If all these tests are passed. the display will shon
the software revision level for about I second similar to
the example below:

SoFt 1.1

3-6. Display Messages

The Model 776 has several display messages associated
with basic front panel opcralion The instnuncnt has
also a few front panel indications that flag front panel
programming error. These messages are discussed in the
following. Note that the instrument has a number of
additional display messages which are associated with

IEEE-488 programming.

3-6-l. IEEE-488 Error Messages

The counter incorporates a number of display messages
which are associated with errors made through the GPIB
interface. These messages are discussed in detail in
Section 4 of this manual. However. there is one message
which should be esplaincd at this point because it may
interfere with normal front panel operation A remote
enable or a device dcpcndent command. sent to the
counter through the bus. turns on the REMOTE light

FUNCTION

Function
Display/Modify
Gate/Delay Time I.0 s
Trigger Levels A & B 0.00 v
Coupling DC
Slope
Attenuators

Filters Off
impedance lMX2

Averaging
Auto Trigger
Delay Off
Sampling Rate
Ratio Mode A/B

V Peak A
Totalize Mode
Displayed Digits
IEEE Status Local

Note: The Model 776 and 776/2,4G/R have a de­fault gate time of I second. The Model
776/2.4G/R has a default gate time of IOOms.

___~~~~~~DEFAULTSTATE~~.~~~~~_

Frequenn A
Normal reading

Positive going
off

Off
Off

Normal - 3 reading/s
Rate Fast

Infinite

10

1. Any two front panel push-buttons are pressed simul-

taneously except the two [VERNIER] push-buttons.

2. The instrument is in FREQ or RATIO or TIME AVG
function and the operator attempts 10 turn the delay on.

3. The instrument is in FREQ or RATIO function and
the operator attempts to turn the AVG function on.

4. The instrument is in rcmolc condition (REMOTE

LED on) and any front panel push-button except

[CLR/LCL] is pressed.

5. The [VERNIER] push-buttons were pressed and the
instrument was not in DISPLAY/MODIFY mode of
operation.

6. The instrument was in DISPLAY/MODIFY tnode of

operation and the [VERNIER fi] or [VERNIER u]
push-buttons were pressed continuously until a parame­ter limit was reached. Parameter limits are summarized
in Table 3-2.

2. GATE ERROR. The gate error is indicated on the
front panel by the GATE LED. This error will occur
when the counter is in FREQ or TIME AVG function
and when the signal was removed from the input con­nector in the middle of the measurement process or
when a radiated random noise was sensed by the input
circuitry. The GATE LED will then blink once but no
result will be registered on the display.

Table 3-1.

and enables remote operation. In this case. all front
panel push-buttons. except [LCLJ. are disabled. An
attempt to press one of these push-buttons will cause the
following message to be displayed:

This message indiiates that the inswument will ignore

any front panel programming scquencc unless the

[CLRlLCL] push-button is pressed and the REMOTE

light turns off.

Dejiiult Stntcs After Sojiivnre Reset

PrESS LcL

3-6-2. Error Indication

There are several error indications that are caused bj
either an incorrect front panel programming or insuffi­cient input level conditioning which is otherwise re­quired by the instrument for normal signal processing,
These indications are either visible (blinking LED) or
audible (beeper) and are described in the following.

1. AUDIBLE ALARM. The AUDIBLE ALARM will
sound when attempting an incorrect sequence of front
panel programming. This could occur under the follow­ing conditions:

3. GATE TIME ERROR. The gate time error is indi­cated on the front panel by the GT LED. The gate time
erroroccurs in FREQ or TIME AVG functions when the
period of the input signal is larger than the period of the
gate time. The gate error will also occur in Phase A to
B functiou when the gate time is no1 sufficient to permit
the minimum resolution of 1 degrees. When one of the
conditions above occurs. the gate time LED (GT) will

blink for a couple of times and then resume a search

routine. This sequence will rcpcat itself until a proper
signal is found or until the gale time was readjusted to
satisfy the required conditions.

4. TRIGGER LEVEL ERROR. The trigger level error
occurs when the instrument is set to AUTO TRIG or V
PEAK A modes and the input signal is either absent or
below lhe specified auto trigger limils. The trigger level
LED (either TL A or TL B) then blinks. for a couple of
times. The counter 1hen resumes a new search routine.
This sequence will repeat itself until a signal has been
found or until the auto trigger mode was turned off.

3-7. Control Selection

Selecting the various from panel operating modes is
simply a matter of pressing. once or 1wice. the appropri-

ate push-button as dcscribcd in the following para­graphs.

3-5

Opernting Instrlrctions

FRONTPANEL
NOMENCLATURE PA&+ETF.$.

TL A Trigger Level A
TL B Trigger Level B

GT

Gate Time
DLY Delay Time
DIGITS

No of displayed digits

ADRS GPIB address

Table 3-2.

Front Panel Progrmnnring Limits

3-8. Selecting A Function

The Model 776 must be set up. for the proper measuring
function. with one of the three Function push-buttons.
There are 17 different available functions in the FUNC­TION block summarized in the following. To simplify
the operating instruction for these functions. the fuuc­tions are divided in the following table into three opera­tional groups.

FUNCTIONS SUMMARY

Group 1

1. FREQUENCY A

2. FREQUENCY B

3. FREQUENCY C

4. PERIOD A

5. PULSE WIDTH A

6. TIME INTERVAL A TO B

7. PHASE A RELATIVE TO I3

Group 2

8. PERIOD AVERAGED A

9. PULSE WIDTH AVERAGED A

10. TIME INTERVAL A TO B AVG

Group 3

11. TOTALIZE B (infinitely)

12. TOTALIZE B GATED BY A

13. TOTALIZE B GATED BY AA

14. RATIO A/B

15. RATIO CIB

16. V PEAK A -FAST RATE

17. V PEAK A - SLOW RATE

The letter after the function indicates the input conuec­tor where this measurement may be performed. For

-5.00

-5.00
100 ps
100 ps

3
0

+5.00
+5.00

100 s I USER GATE
100 s / USER DELAY

10

30

example. FREQUENCY C can only be measured if the
signal is applied to the C Channel input

COIUKX~OT.

Similarly, V PEAK A can only be measured at the
Channel A input connector. Some functions require that
both Channel A and B be connected for a successful
measurement - functions like Time Interval A to B.
Ratio FRQ/B. OT Totalize B by A.

Selecting a function from the first group is described

in the following:

1. First bring the Model 776 to a known state as de-

scribed in paragraph 3-5. This is done by pressing first
the [2nd/EXE] push-button and then pressing the

(DCL] push-button. The instrument will then defaull to

a factow pre-selected state and the light next FRQ A
will illuminate: indicatiug that Frcqucucy A function is

now selected.

2. To select Frequency B press the [FREQ] push-button

once. The light next to FRQ B illuminates: indicating
that Frequency B is now selected.

3. To select Frequency C press the [FREQ] push-button

again. The light next to FRQ C illuminates: indicating
that Frequent) C is noyI’ selected. Note that this proce-

dure assumes that option 52 (2.4 GHz C Channel is
installed).

1. To select Period A press the [TIME] push-button

once. The light next to PER A illuminates: indicating

that Period A is now selected.

5. To select Pulse A press the [TIME] push-button
again. The light uest to PLS A illuminates: indicating
that Pulse A is uow selected.

6. To select Time Intenal A to B press the [TIME1
push-button again. The light next to TI A to B illumi­nates: indicating that Time Intenxl A to B is no\\ sc­&ted.

3-6

7. To select Phase A re1atix.e to B press the [RATIO]
push-button again. The light next to Phase A to B illu­minates: indicating that Phase A to B function is now
selected.

Select

a function from the second group as

described in the following:

8. To select Period Averaged A press the [TIME] push­button until the light nest to PER A illuminates. Press
the [2nd] push-button and then press the AVG. push­button (second function to the [TIME] button). Ob-

serve that the AVG light illuminates: indicating that the

Period Averaged A function is non selected.

9. To select Pulse Averaged A press the [TIME] push­button until the light next to PLS A illuminates. Press
the [2nd] push-button and then press the AVG. push­button (second function to the TIME button). Observe
that the AVG light illuminates: indicating that the Pulse
Averaged A function is now selected.

10. To select Time Interval Averaged A to B press the

[TIME] push-button until the light next to TI A to B
illuminates. Press the ]Znd] push-button and then press
the AVG. push-button (second function to the TIME
button). Observe that the AVG light illuminates: indi­cating that the Time Interval Averaged A to B function
is now selected.

This reading indicates that the instrument is set to To­talize infinitely. Now press the [VERNIER UP] push­button once and observe that the display reading is
changed to the following:

tot bY A

This reading indicates that the instrument is now set

to Totalize at B with A serving as the gating signal.

Press the [GT] push-button again. The instrument is
now ready to perform the required function.

13. To select Totalize B by AA function repeat the

procedure as described above. Pressing the [VERNIER

fi] push-button changes the display reading as follows:

tot bY AA

This reading indicates that the instrument is no% set

to Totalize. at B input. with a pair of consecutive tran-

sitions at A. having the same direction. seming as the

gating signal. Press the [GT] push-button again The

instrument is now ready to perform the required func-

tion.

14. To select Ratio A/B press the [RATIO] push-button
again. The light nest to FRQ/B illuminates: indicating
that Ratio A/B is no!v selected.

NOTE

The averaging function. once it is se­lected. will automatically turn on
whenever a TIME measuring func­tion is selected. For example. Select­ing PER A averaged turns the AVG
light on. Changing the selected func­tion to FRQ A will automatically- turn

the AVG light off. Re-selecting one of
the TIME functions will automati­cally turn the AVG light on.

Selecting a function from the third group requires

additional operations and is described in the following:

11. To select Totalize B press the [RATIO] push-button
once. The light next to TOT B illuminates: indicating
that Totalize B is now selected.

12. To select Totalize B by A function press the [RA­TIO] push-button until the light next to TOT B illumi­nates. The counter is now set to totalize indefinitely.
To select the Totalize B by A function press the [GT]
(gate) push-button in the DISPLAY/MODIFY group
and observe that the reading on the display is as follows:

tot InF

15. To select the Ratio C/B function press the [RATIO]
push-button until the lighl nest to FRQ/B illuminates.
The counter is now set to measure Ratio FRQIB. To
select the Ratio C/B function press the (2ndj and [FRQ
SEL] (frequency select) push-buttons in sequence and
observe that the reading on the display change to display
as follows:

A to B

This reading indicates that the instrument is set to

Ratio A/B. Now press the [VERNIER fl] push-button
once and observe that the display reading is changed to
the following:

C to B

This reading indicates that the instrument IS now set
to Ratio C/A. Press the [2nd/EXE] push-bulton again.
The instrument is now ready to perform the required
function.

16. The V Peak A function has two measurcmcnt rates:
Fast - for frequencies above IO0 Hz and Slow - for the
range of 40 Hz to 10 MHz. Note that the inslrument.
after DCL defaults to its Fast ram. Selecting the meas­urement rate is described later in this mauual.

3-7

Opernting Instnrctions

3-9. Selecting Gate And Delay Time

The Model 776 may be operated in its preset gate or
delay times of one second. or with one of its 500 built-in

increments. When selecting the gate time. the instru­ment will increment up or down. one gate time. each
time the [fi] or [u] push-button is pressed. The present
gate time may be noted oo the display by pressing the

[GT] push-button.

The gate times may only be selected in conjunction
with frequency. time averaged. ratio FRQ/B_ and Phase
A to B functions.

The gate time may be selected as follows:

1. Select a frequency measurement function.

2. Press the [GT] push-button. Obsewe that the GT light
turns on and that the instrument displays the following
message:

1.0

This reading indicates the selected gate time in sec-

onds.

3. To change the gate time press the [VERNIER fl] or
[VERNIER 111 push-buttons. Pressing the [I?] push-but-

ton increases the value of the gate time. Conversely.
pressing the [DOWN] push-button decreases the value

of the gate time. Depressing the [l?] or [u] push-buttons
for more than 1 second. causes the instrument to incre­ment or decrement contirwously.

4. Pressing the [fil push-button and the instrument was
at a gate time of 100 seconds forces the instrument into
a USER GATE mode. This mode requires an external
gating signal. Operating the counter with an external
gate is explained later in this section.

5. Pressing the [l?l and [u] simultaneously changes the
gate time to a preset value of 1.0 second.

6. To resume normal display operation. press the [GT]
push-button. The GT light turns off and the instrument
is now ready to perform measurements with the newly
selected gate time.

NOTE

To prevent operator error. there is an
internal audible alarm that sounds
whenever a limit is reached. (e.g low
limit of 100 ps).

The sequence of selecting the delay time is similar to
the procedure for selecting the gate time. Delay times
may only be selected and applied to single shot (non-av-

eraged) time measurement. To select a delay time value

proceed as follows:

1. Select a single shot time measurement function such

as Period. Pulse Width. or Time Interval A to B.

2. Press the IDLY] push-button. The DLY light turns on

and the instrument displays the following mcssagc:

1.0

This reading indicates the selected delay time in

seconds.

3. To change the delay time press the [VERNIER 01 or
[VERNIER u] push-buttons. Pressing the [fi] push-but­ton increases the delay time. Conversely. pressing the
[u] push-button decreases the delay time. Depressing
the [I?] or [u] push-buttons for more than 1 second.
causes the instrument to increment or decrement con-

tinuously.

4. Pressing the [fl] push-button and the instrument was
at a delay time of 100 seconds forces the instrument into
a USER DELAY mode. This mode requires an external
delay signal. Operating the counter with an external
delay is explained later in this section.

5. Pressing the [fl] and [u] simultaneously changes the
delay time to a preset value of 1.0 seconds.

6. To resume normal display operation. press the IDLY]
push-button The DLY light turns off and the instrument
is now ready to perform measurements with the newly
selected delay time.

3-10. Setting Trigger Levels

There are two trigger level push-buttons associatedwith

each Channel A (TL A) and Channel B (TL B). The

[VERNIER fi] and [VERNIER u] push-buttons. when
operated in conjunction with TL A or TL B. set
voltage level that will trigger the instrument. To set the
trigger levels proceed as follows:

NOTE

The procedure for setting the trigger

level is identical for Channels A and
B. Trigger level A (TL A) can only be
modified when functions that are re-

lated to input A are selected. e.g. FRQ
Al TIME A to B etc. Selecting a func­tion which involves Channel B en­ables access to the TL B parameter.

1. Using the procedure which is described above. set the

instrument to Frequency A function. If other front panel

the

3-8

lights illuminate, reset the counter using the software

reset procedure which is described in paragraph 3-5.

To set input condition controls for Channel A pro-

ceed as follows:

2. Press the ]TL A] push-button. Observe that the TL A
and VOLTS indicators turn on and that the display reads
as follows:

0.00

This reading indicates the selected trigger level in

units of volts.

3. To set a positive trigger level press the [VERNIER
fi] push-button. Holding in the [I?] or [u] push-buttons

for more than I second. causes the instrument to incre­ment or decrement continuously. To set a negati\:e trig-

ger level press the [VERNIER u] push-button until the

desired level has been reached.

NOTE

Pressing the [VERNIER fl] or [VER­NIERU] push-buttons. when the lim-

its of +5.00 or -5.00 respectively have

been reached. causes

alarm to sound.

4. Simultaneously press the two [VERNIER] push-but­tons and note that the display reading resets to 0.00.

5. Press the [TL A] push-button. The indicator light
turns off and the instrument returns to its previous
measurement state.

6. To set the trigger level for both Channels A and B.
select a function which involves both inputs (eg ratio
A/B. Phase A to B. time intenjal A to B or totalize B by
A). Pressing the [TL] push-button once turns the TL A

light on: indicating that the instrument displays the
trigger level for Channel A. A second consecutive press
turns the TL B light on: indicating that the instrument
displays the trigger level for Channel B. A third push
turns TL B light off. The instrument then resumes its
normal operation.

an

audible

3-11. Setting Input Conditioning

Controls

A proper set-up of the input controls ensures proper
operation of the instrument. There are five push-buttons
which control the input. These push-buttons are com­mon to both Channels A and B.

Changing one of the input setting controls is simply

a matter of pressing the required push-button. There are

5 lights for each input channel which are associated with

each of the five controls.

1. Set the instrument to operate al one of the following

functions: FRQ A. PER A. PLS A. or V Peak A.

2. To select the required coupling mode press the [AC]

push-button. Instrument is dc coupled when the AC

light is off. When the AC light is on the instrument is

ac coupled.

3. To change the slope that the instrument will trigger
on. press the [SLOPE] push-button. The counter trig­gers on a positive going edge if the slope light is off. If
the slope light is on the counter triggers on a negative

going edge.

4. Attenuation is required when the inpur signal exceeds
the specified dynamic range. To attenuate the signal
press the [x10] push-button, The input signal is allenu­ated by a factor of 10 when the x10 light is on. When
the x10 light is off. the input signal is not attenuated.

5. In low frequency applications. where the frequency
range is below 100 KHz. it is recommended to use the
low pass filter. The low pass filter attenuales the high

frequency components which may interfere with the

required measurement. To apply a low pass filter press
the [LPF] push-button. High frequency signals are fil­tered when the LPF light is on. The filter is deactivate
when the LPF light is off.

6. In high frequency applications above 1 MHz. or high
slew rate signals. it is rccommcnded that the input cable
be terminated with 50 R at the counter end. To change

the input impedance from 1 Mn to 50 n press the 150
n] push-button. Input is termination with 50 0 when
the SO Cl light is on Input impedance is I MCI when the
50 0 light is off.

To set input condition controls for Channel B pro-

ceed as follows:

1. Set the instrument to operate in one of the following
functions: FRQ B or TOT B.

2. Use the same procedure as described above for Chan­nel A.

To set input condition controls for both Channcl~ A

and B proceed as follows:

1. Set the instrument to operate in one of the following

functions: Time Interval A IO B. Ratio FRQ/B. Phase A

to B. TOT B by A. or TOT B by AA.

2. To select the AC coupling mode for Channel A. press
the

[AC]

push-button once. The AC A lighl illuminates:

3-9

indicating that Channel A is now ac coupled. Pressing
the [AC] push-button again turns the AC A light off but
AC B light turns on: indicating that Channel A is dc
coupled and Channel B is ac coupled. Pressing the
button once more. turns both AC A and AC B light on:
indicating that both channels arc now ac coupled.
Pressing the same push-button again turns both lights
off. This now indicates that both channels are set to dc
coupling mode.

3. Use the same procedure to set the slopes. attenuation.
impedance and filtering.

processed measurement with the programmed number
of digits.

NOTE

Selecting five
instead of ten. will eliminate the five
least significant digits and will move
the entire display to the right by five
places. An example of a normal dis­play reading. and the same display
reading with five digits of resolution
is given as follows.

digits

to be displayed.

3-12. Selecting The Number Of

Displayed Digits

A major advantage of Model 776 over similar products
is its capability to display a fixed number of digils
regardless of the frequency of the input signal. For

example. with one second of gate time. the Model 776
displays a minimum of 10 digits. This however. may
turn into a disadvantage when measuring the frequent)
of a relatively unstable signal: in which just the most
significant digits are stable and the least significant
digits are “jumping around” with no significant mean­ing. Model 776 permits truncation of the unstable
significant digits. while still preserving its full perform­ance. To select the number of displayed digits proceed
as follows:

1. Press the [2nd] push-button. Observe that the instru­ment prompts the following message:

2nd ?

2. Press the [DIGITS] push-button (second function to
]AC A]). The instrument now displays the following:

xx diGit

Where s is the selected number of digits and could range
from 03 to IO digits.

3. Use the [VERNIER fi] to increase the number of the

displayed digits. Conversely. press the [VERNIER u]
to decrease this number.

4. Pressing the [VERNIER ft] and [VERNIER u]

simultaneously. presets ss to IO: indicating that results
will be displayed with up to IO digits of resolution. and
that no digit will be truncated.

5. To return to normal operation of the Model 776

simply press and release the [EXE] push-button (second
function to [2nd]. The instrument than displays the

least

Display reading w~ith IO digits:

1.234567890

Display reading with selected 5 digits:

1.2345

NOTE

Under certain conditions. Model 776
may display frequency reading with

less than ten digits. This may occur
when the selected gate time is smaller
than 1 .O second. In that case. the in­strument overrides the programmed
pm-selected number of digits and dis­plays only as many digits as it can.
When gate time is increased. Model
776 again limits the number of dis-

played digits to the selected value.

3-13 Selecting Measurement Rate

Model 776 offers a choice from three measurement
rates. Two measurement rates are accessible through
front panel programming - normal rate (about 3 readings
per second). and single shot (hold). A fast measurement
rate (up to IO0 reading per second) is also available but
is only accessible from the GPIB interface. The fast
measurement rate will be discussed in details in Section

4. The HOLD light determines front panel measurement
rate. When the indicator is off. the instrument is in its
normal measurement rate. When the HOLD light is on.
the instrument is set to single shot measurements. To
select the measurement raw proceed as follows:

1. Press. in sequence. the [ZndlEXE] and the [HOLD]
push-buttons (second function to IRATIO]). The
HOLD light turns on: indicating lhat the instrument is

now~ armed for a single-shot measurement cycle. Arm­ing is explained later in this chapter.

3-10

2. To return to normal measurement rate. press. in se-

quence.
[HOLD]

the

[2ndlEXE]

push-button and then the

push-button. The HOLD light turns off: indi­cating that the instrument is now ready to accept and
process readings at its normal rate.

3-14-2 Front Panel Arming

Front panel arming is performed with the
button. To use front panel arming proceed with the
following steps:

[CLR]

push-

NOTE

Measurement rate is gate time de­pendent. Model 176 can process 3
readings in one second when its gate
time is set to below 300 ms.

3-14 Arming

Capturing the required sequence of input signals may.
at times. create a major problem for the design engineer.
Imagine a single source that repeatedly generates bursts
of signals having various repetition rates. pulse widths.
and number of pulses. It would be next to impossible to
measure such parameters along the time axis unless the
counter is prepared for this task. Model 776 has arming
capabilities which permits such complex measure­ments. Do not confuse arming with Trigger. Model 776
may not be triggered. Model 776. unless armed. will not
perform the task of signal processing. Model 776 may
be armed (prepared) for the next measurement in four
ways:

1. Continuously armed by an input signal. when Model
776 is set to its normal mode of operation.

2. With front panel
ment is set to HOLD mode.

3. With an arming pulse applied to the rear panel EXT.
INPUT connector. when the instrument is in the HOLD
mode.

1. With commands given over the IEEE-488 bus as
described in Section 4. This section covers front panel
and external arming in details.

3-14-1 Continuous Arming With the

Input Signal

When no special arming mode was selected. Model 776
is armed by its input signal. This means that with no
legal input signal, the counter idles. The Gate indicator
is off until the first transition. at the input connector. is
sensed. An input signal. within the dynamic range.

initiates a measurement cycle. The gate light blinks

every time that the internal gate opens. There is no

special procedure to set the Model 776 up for continu-

ous arming. This mode is especially useful in analyzing

the contents of a burst.

[CLR]

push-button. when the instru-

1. Using the procedure described in paragraph 3-13.

select the hold mode. Obsewe that the HOLD light turns
on and that the gate light ceases from flashing: indicat­ing that the instrument is in its one-shot measurement
mode. The display zeroes and no reading is processed
until an arming stimulus is applied.

2. To arm the instrument for a single reading. press and
release the

[CLR]

push-button. The nest transition at
the input connector will cause the gate to open. The
instrument then checks for the legality of the input
signal. processes the reading and displays the result on
the display. The display will retain the last processed
reading until cleared, re-armed. or until another func­tion is selected.

3. To arm the instmment for a new measurement. press
the

[CLR]

push-button. Obsewe that the display zeroes

sod that a new measurement cycle is initiated.

4. To remove the instnunent from its one-shot arming
mode. turn the hold fuoctionoff by pressing in sequence
the [2nd] and

[HOLD]

push-buttons.

3-143 External Arming

External arming operates much like front panel arming
except for the arming stimulus itself. In this case the
arming stimulant is applied to the rear panel EXT. IN­PUT connector. The arming pulse must conform to TTL
levels. To use the external arming feature. proceed as
folloas:

1.

Using the procedure described in paragraph 3-13.
select the hold mode. Observe that the HOLD light turns
on and that the gate light ceases from flashing: indicat­ing that the instrument is in its one-shot measurement
mode. The display zeroes and no reading is processed
until an arming stimulus is applied.

2. Connect the external arming source to the rear panel
EXT INPUT connector. The first positive going transi­tion at the EXT INPUT connector arms the Model 776
for taking and processing the nest available signal.
Note that after each positive going transition of the
arming signal. the numeric display is set IO read zero
until the next data is processed and displayed. Model
776 ignores any transitions at the EXT INPUT

tar

when the gate is open.

connec-

3-l I

3. To remove the instrument from its one-shot arming
mode, turn the hold function off by pressing in sequence
the [2nd] and [HOLD] push-buttons.

3-15. Using Auto Trigger Level

The auto trigger level function is extremely useful when

measuring repetitive signals having an unknown dc
component. The auto trigger is capable of finding the
peaks of the signal and then setting the trigger level

exactly at their center. In addition. The auto trigger
automatically sets the correct attenuation and adjusts
the input signal to fit within the dynamic range. The auto
trigger mode does not operate on totalize B and fre-

quency C functions. Auto trigger level function works

independently in conjunction with Channels A and B.

To set the Model 776 to operate in auto trigger mode

proceed as follow:

1. Press in sequence the

(second function to [TL A])push-buttons. Observe that
the AUTO TRIG light illuminates: indicating that the
auto trigger function is selected. When the indicator is
off. the instrument is in its normal manual trigger level

mode.

2. Apply the signal to be measured to the appropriate

input connector. After a short search sequence. the gate

opens and the measurement is processed.

3. TL A or TL B lights blink if an error was detected.

Refer to paragraph 3-6-3 for a additional error indica-

tions information.

[2nd]

and the

[AUTO

TRIG]

0.00 0.00

The three
amplitude.

digits on the left indicate the lower peak

The right three digits indicate the higher

peak amplitude. Negative values have a leading minus

sign where positive values have no sign. The minus sign

and the decimal points are automatically set by the

instrument.

2. To select the measurement rate press the

[CT]

push-

button in the DISPLAY/MODIFY group and obscrvc

that the reading on the display is as follows:

FASt

This reading indicates that the instrument is set to its

fast measuring rate.

Now

press the

[VERNIER fi]

push-

button once and obsene that the display reading is

changed to the following:

SLO

This reading indicates that the instrument is set to

measure the V Peak A with its slow measuring rate.

Press the [GT] push-button again. The instrument IS

now ready to perform the required function.

3. Press the [GT] push-button to return the counter to
normal V Peak display.

4. Press one of the FUNCTION push-buttons to select
another function. Observe that the display returns to
normal display reading and that the VOLTS light turns
off.

4. To return the Model 776 to normal trigger level mode.
press in sequence the

[2nd]

and the [AUTO TRIG]

push-buttons.

3-16. Using V Peak A

The V PEAK A function turns the Model 776 into a
versatile RF peak voltage meter where both lou and
high peaks are detected. processed and displayed. This
is especially useful in analyzing both the amplitude and
the dc component of an unknown signal. Their are two
available measurement rates for the V Peak function:

Fast for normal measurements abol-e IO0 Hz. and slow
rate for measurements of signals belox\ 100 Hz. To
select the V Peak A function proceed as follows:

1. Press in sequence the [2nd] and the
function to [FREQ]) push-buttons. Obseme that the
VOLTS light illuminates. This indicates that the instru­ment is now set to V Peak A measurements. The normal
display reading is transform into a two section display
like the following:

3-12

[V PK A]

(second

3-17. Using User Gate

The User Gate is useful when a gate time other than the
internal pre-determined gate times is rcquircd. The lim­its which must be observed are the mininwtn limit of

100 yS and the maximum limit of IOOO s. The User Gate
function is accessible in FRQ A. B and C. FRQIB. PER
AVG. PLS AVG. and TI AVG A to B operating modes.
To operate the instrument in its User Gate mode proceed
as follows:

1. Set the instrument to PRQ A. Press the
button once. 0bsen:e that the Gate light turns on, and
that the instrtunent displays the gate time.

2. Press and hold the

[VERNIER

n] push-button and
obsense that the display increments. Afler the 100 s gate
time the instrument enters the User Gate mode and
displays the following readout:

USEr GAtE

[GT]

push-

Depressing the

[VERNIER

fi] push-button after the

usergate is displayed causes an audible alarm to sound.

3. Press the

[CT]

push-button. The Gate light turns off
and the instrument is now ready to perform measure­ments with an external gate time.

6. To return to normal operation depress in sequence the
[2nd] and the

]GT/DLY]

push-buttons. The DELAY
light turns off: indicating that the instrument will no
longer delay the closure of its gale.

NOTE

4. Apply an external TTL pulse to the rear panel EXT
INPUT connector. This signal now serves as the ester­nal gate time. The high level duration of the external
pulse determines the period of the gate time.

5. To exit the User Gate function press the
u] push-button. Pressing both the

[VERNIER

u] push-buttons presets the displayed gate

[VERNIER

[VERNIER

fi] and

time to 1 .O 5.

3-18. Using Delay

The Model 776 has a delay function which inhibits the
closure of the opened gate for a pre-determined period.
This function is very useful in burst measurements.
relay open/close time measurements where bounce time
should be eliminated, and in measurements done on a
train of pulses. The delay function is accessible in PER
A. PLS A. and Time Interval A to B. The delay time ma)
be selected using the following procedure:

1. Set the instrument to [PER
push-button in the DISPLAY/MODIFY group. Obserw
that the DLY light turns on and that the instrument
displays the delay time.

2. To change the delay time. press the

[VERNIER

u] push-buttons. Whenone ofthe ]fi] or [u]
push-buttons are depressed for more than one second.
the instrument increments or decrements continuously.

3. Depressing simultaneously the
the

[VERNIER

u] push-buttons modifies the delay time

to a preset value of 1.0 s.

4. To resume normal display. press the
ton. The DLY light turns off. When enabled. the instru­ment performs measurements with the newly selected
delay time.

5. To enable the delay mode. press the [2nd] push-but­ton and then the

[GTIDLY])

push-button. Obsewe that the DELAY light

[DELAY]

illuminates. This indicates that the instrument is now set

to operate in its delay mode. The delay light turns off
automatically when another function. other than from
those specified above. is selected. Conversely. return-

ing to one of the above functions restores the delay
mode.

A].

Press the

[VERNIER fi] or

[VERNIER

IDLY]

IDLY]

fi] and

push-but-

(second function to

To prevent operator’s error. there is
an internal audible alarm that beeps
whenever a limit is reached. (e.g 100
~5 low limit).

3-19. Using User Delay

The User Delav is useful when a delay time other than

the pre-determined delay times is required. The limits
which must be observed are the minimum limit of 100
ps and the maximum limit of 10.000 s. The User Delay
function is accessible in PER A, PLS A. and Time
Interval A to B operating modes. To operate the instru­ment in its User Delay mode proceed as follow:

1. Set the instrument to PER A. Press the IDLY] push­button once. Observe that the DLY light turns on. and
that the instrument displays the delay time.

2. Press and hold the [VERNIER n] push-button and
observe that the display increments. Afler the 100 s
delay time the instrument enters the User Gate mode and
displays the following readout:

USEr dLAY

Depressing the [VERNIER I?] push-button after the

user gate is displayed causes an audible alarm to sound.

3. To resume normal display. press the [DLY] push-but­ton. The DLY light turns off. When enabled. the inslru­ment performs measurcmcnts with the user delay time.

4. To enable the user delay mode depress in sequence
the [2nd] and the [DELAY] (second function to

[GT/DLY]) push-buttons. Obsewe that the DELAY
light illuminates. This indicates that the instrument is

now set to operate in its User Delay mode. The delal
light turns off automatically when another function.
other than from those specified above. is selected. Con­versely. returning to one of the above functions restores
the delay mode.

5. Apply an external TTL pulse to the rear panel EXT
INPUT connector. This signal now senzs as the ester-

nal gate time. Delay is then enabled as long as this input

is kept at TTL high level. The first negative transition
to TTL low disables the delay. The delay is then dis-

abled as long as this input is kept at TTL low level.

3-13

Operating Instructions

3-20. Using Front Panel Set-Ups

Setting up all parameters in a versatile instrument such

as the Model 776 may takes some time. The set-up time

is even longer when more than one set-up is required.
Model 776 incorporates a battev backed-up non-vola­tile memory that preserves stored information up to
three years. It is possible to store complete front panel
set-ups in 10 different memory locations which are built
into the instrument especially for this purpose.

3-20-l.

First modify the front panel parameters as necessav to

perform your tasks. When all parameters are set and
checked. proceed to store this set-up as follows:

1. Depress the [ST01 push button and observe that the

display is modified to indicate the following:

receive one memory location where front panel set-up
is to be stored. Set-ups may be stored in locations 0 to

9. Depressing [STOJ again cancels this function and the
instrument resumes normal operation.

2. Select one memory location from 0 to 9 and depress
the button which is marked with the selected number.
The instrument displays the following for one second:

(Where D is the selected memory location)

acknowledges the entered memom location. The instru­ment then resumes normiil opcraiion.

3-20-2. Recall Set-Ups

Store

This reading indicates that the instrument is ready to

This display indicates that the function generator

Set-Ups

StorE ?

(? appears flashing)

StorE D

rEcALL ?

(?

appears

This reading indicates that the instrument is ready to
recall the memory location where front panel set-up was
stored. Depressing the [RCLI button cancels this func­tion and the instrument resumes normal operation.

2. Select one mcmo~ location from 0 to 9 so as to recall
the desired set-up. and depress the button which is
marked with the selected number. The instrument dis-

plays the following for One second:

rEcALL D

(Where D is the selected

The instrument then recalls the parameters that were
previously stored in the selected memory location and
updates front panel indicators with the recalled parame­ters.

flashing)

memory location)

3-22. Using An External Reference

Generally. Model 776 provides two accuracy grades for
the internal time base: stabilized clock. or an optional
temperature compensated crystal oscillator (TCXO).
The best accuracy. over the specified temperature oper­ating range. that may be achieved with the TCXO is I
PPM. or 0.1 PPM -accuracy which will satisfy the most
demanding requirements. With special applications.
however. where such inaccuracies may become a limil­ing factor. an external reference ma) provide a better
solution. An EXT REF comiector is available on the rear

panel. However. before applying an esternal rcfcrcncc
signal. it is first neccssaq to open the top cover and
change a switch setting. The procedure of changing this
switch is given in Section 5 of this manual.

Turning AC Mains power off does not affect the stored
data in the RAM. Therefore. front panel set-up which
were previously recorded by the user remain presened.
To recall a front panel set-up proceed

I. Depress the [RCL] push button and observe that the

display is modified to indicate the following:

3-11

as follows:

3-23. Changing GPIB Address

GPIB address is modified using front panel program­ming. The non-volatile memov stores the GPIB ad­dress. Conventional address switches are not provided.
Detailed instructions how to change the GPIB address
are given in Section 4 paragraph -i-7.

IEEE-488 Operation

1. Introduction

The IEEE-488 bus is an instrumentation data bus with
standards adopted by the IEEE (Institute of Electrical
and Electronic Engineering) in 1975 and given the

IEEE-488 designation. Model 776 conforms to this

standard - in full.

This section contains general bus information as
well as detailed programming information and is di­vided as follows:

1. General introductoo information pertaining to the
IEEE-488 bus may be found primarily in paragraphs 4-2
through 4-5.

2. Information necessary to connect the Model 776 to
the bus and to change the bus address is contained in
paragraphs -1-6 and 4-7.

3. Programming of the instrument with general bus
command is covered in paragraph 4-S.

4. Device-dependent command programming is de­scribed in detail in paragraph 4-9. The commands out­lined in this section can be considered to be the most
important since they control virtually all instrument
functions,

5. Additional information pertaining to front panel error

messages and controller programs can be found in para-

graphs 4-11-1 and J-11-2.

4-2. Bus Description

the bus has only eight data lines which are used for both

data and most commands. Fiw bus managcmcnt lines

and three handshake lines round out the complcmcnt 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 remote controlled
operation is shown in Figure 4-I. The typical system
will have one controller and one or more insttumcnts to
which commands are given and from which data is

received. There are three categories that describe device

operation. These include: controller: talker: listcncr.

The controller controls other devices on the bus. A

talker sends data. while a listener rcceivcs data. an
instrument. may be a talker only. a listener only. or both
a talker and listener.

Any given system can have only one controller (con-

trol may bc passed to an appropriate device through a
special command). Any number of talkers or listcncrs
map be present up to the hardnarc constraints of the bus.
The bus is limited to IS devices. but this number ma!
be reduced if higher than normal data trausfer rates arc
required or if long interconnect cables are used.

The IEEE-488 bus was designed as a parallel data trans-

fer medium to optimize data transfer without using as

excessive number of bus lines. In keeping with this goal.

Several devices may be commanded to listen at once.
but onlv one device may be a talker at any given time.
Othcr&c. communications would be scrambled much

4-l

IEEE-488 Operation

Figure

4-1. IEEE Bus Conjiguration

like an individual is trying to select a single conversa-

tion 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 command derived from its primary ad­dress. Normally, each device on the bus has a unique
primary address so that each may be addressed individu­ally. The bus also has another addressing mode called
secondary addressing, but not all devices use this ad-

dressing mode.

Once the device is addressed to talk or listen,

appropriate bus transactions may be initiated. 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 is then be used to chan­nel the information to the desired location.

4-3. 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 assurc that proper data lransfcr and bus

operation takes place. Each of the bus lines is “active
low” so that approximately zero volts is a logic “one”.
The followingparagraphsdescribe the purposeofthese
lines, whichare showninFigure4-1.

4-3-l. Bus Management Lines

The bus management group is made up of five signal

lines that provide orderly transfer of data. These lines
are used to send the uniline commands described in
paragraph 4-S- 1.

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 4-S-2.

2.

IFC

(Interface Clear) - Setting the IFC line true (low)

causes the bus to go to a known state.

3.

REN

(Remote Enable) - Setting the REM line low
sends the REM 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

a device when it requires service from the controller.

is

set low by

4-2

DA”

SOURCE

VALID

NAFO

I

I
I

I
,

I

DATA

TRANSFER

BEGINS

Figure

NDAC

4-2. IEEE Handshake Sequence

4-3-Z. Handshake Lines

The bus uses three handshake lines that operate in an

interlocked sequence. This method assures 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
source, while the remaining two lines arc controlled by
accepting devices. The three bus handshake lines arc:

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 con-

trols the NDAC line.

data

I

ACCEPTOR

I
I

ACCEPTOR

I

DATA

TRANSFER

ENDS

lers have time-out routines to display error messages if
the handshake sequence stops for any reason.

Once the NRFD and NDAC lines are properly set,
the source sets the DAV line low, indicating that dataon
the bus is now 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 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 NRFD line is released by each
of the devices at their own rates, until the NRFD 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 complete handshake sequence for one data byte is

shown in Figure 4-2. 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 controller, NRFD and NDAC must re­main stable for at least 100 ns after ATN is set low:
Because of the possibility of bus hang up, some control-

The sequence just described is used to transfer both
data and multiline command. The state of the ATN line
determines whether the data bus contains data or com-

mands.

4-3-3. 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

4-3

IEEE-488 Operation

DIOI through DI08 instead of the more common DO
through D7 binary terminology The data lines are bi-di­rectional and. as with the remaining bus signal lines.
low is true.

4-4. Interface Function Codes

The interface function codes are part of the IEEE-488-

1978 standards. These codes define an instrument’s
ability to support various interface functions and should
not be confused with programming commands found
elsewhere in this manual.

Table 4-l lists the codes for the Model 776. The
numeric value following each one or two letter code
define Model 776 capability as follows:

SH (Source Handshake Function) - The ability for
the Model 776 to initiate the transfer of message/data
on the data bus provided by the SH function.

AH (Acceptor Handshake Function) -The ability for

the Model 776 to guarantee proper reception of ntes-

sage/data on the data bus provided by the AH function.

T (Talker Function) - The ability of the Model 776
to send device-dependent data over the bus (to another
device) is provided by the T function Model 776 talker
capabilities exist only after the instrument has been
addressed to talk.

L (Listen Function) - The ability of the Model 776
to receive device-dependent data over the bus (from
anther device) is provided by the L function. Listener
function capability of the Model 776 exist only after it
has been addressed to listen.

RS (Service Request Function) - The ability of the
Mode1 776 to request service from the controller is
provided by the RS function.

RL (Remote-Local Function) - The ability of the
Model 776 to be placed in remote or local modes is
provided by the RL function.

PP (parallel Poll Function) - The ability of the
Model 776 to respond to a parallel poll request from the
controller is provided by the PP function.

DC (Device Clear Function) - The ability for the
Model 776 to be cleared (initialized) is provided by the
DC function

DT (Device Trigger Function) - The ability of the
Model 776 to have its output triggered is provided by
the DT function.

C (controller Function) - The Model 776 does not
have a controller function.

TE (Extended Talker Capabilities) - The Model 776
does not have extended talker capabilities,

LE (Extended Listener Function) - The Model 776
does not have extended listener funclion

Table 4-l.

SHl

AH1

T6
IA
SRl

RLl

PP2

DC1

DTl

co
El
TEO
LEO

Model 6030 Interface Function Codes

Source Handshake Function
Acceptor Handshake Capabilities
Talker (basic talker, serial poll.
unaddressed to talk on LAG)
Listener (basic listener. unaddressed
to listen on TAG)
Service request capability
Remote/Local capability
Parallel Poll capability
Device Clear capability
Device Trigger capability
No controller capability
Open collector bus drivers
No Extended Talker capabilities
No Extended Listener capabilities

4-5. 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
paragraph.

Before a controller can be used with the IEEE-488
interface. the user must make certain that appropriate
handler software is present within the controller. With
the IBM PC computer. for esamplc. the GPIB interface

card must be used with an additional I/O ROM. which
contains the necessary handler software.

Other small computers that can be used as control­lers have limited IEEE command capability. The capa-

bilities of other small computers depends on the particu-

lar interface being used. Often. little software “tricks”

are required 10 achieve the desired results.

From the preceding discussion. the message is clear:
make sure the proper software is being used with the
instrument. 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.

4-6. HARDWARE CONSIDERATIONS

Before the instrument can bc used with the IEEE-488
bus. it must be conncctcd to the bus with a suitable
conncclor. Also. the printaT address must be yropcrly
progranmted as described in this scclion.

4-4

4-6-l. Typical Controlled Systems

The IEEE-488 bus is a parallel interface system. As a
result. adding more device is simply
more cables to make the desired connections. Because
of this flexibility. system complexity can range from
simple to extremely complex.

The simplest possible controlled system comprises a

controller and one Model 776. The controller is used to

send commands to the instrument. which sends data

back to the controller.

The system becomes more complex when additional
instrumentation is added. Depending on programming.
all data may be routed through the controller. or it may

be transmitted directly from one instrument to another.

For very complex applications. a much larger com-

puter can be used. Tape drives or disks may then be used

to store data.

a matter

of using

4-6-2. Connections

The instrument is connected to the bus through an IEEE­488 connector. This connector is designed to be stacked

to allow a number of parallel connections on one instru­ment.

NOTES

1. To avoid possible mechanical damage. it is recom-

mended that no more than three connectors be stacked

on any one instrument. Otherwise. the resulting strain
may cause internal damage to the connectors

2. The IEEE-488 bus is limited to a maximum of I.5

devices. including the controller. Also. the maximum
cable length is 20 meters. Failure to obsewe these limits
will probably result in erratic bus operation

Custom cables may be constructed using the infor­mation in Table 4-2. Table 4-2 also lists the contact
assignments for the various bus lines. Contacts I8
through 24 are return lines for the indicated signal lines.
and the cable shield is connected to contact 12. Each
ground line is connected to digital common in the Model

176.

CAUTION

The voltage between IEEE common
and ground must not exceed OV or
damage may result to your instru­ment.

Table J-2.

I DIOI
2 D102
3 D103
4 DIO4
5 EOI
6 DAV
7 NRFD
8 NDAC
9 IFC

10
11 ATN
12 SHIELD

13 D105
I4 D106
15 D107

16 DI08
17 REN

18 Gnd
19 Gnd
20 Gnd
21 Gnd

22 Gnd
23 Gnd
24 Gnd

4-7. Changing

The primav address of your instrument may bc pro­grammed to any value between 0 and 30 as long as the

selected address is different from other devices ad­dresses in the system This may be accomplished using
a front panel programming sequence. Note that the pri-

mary address of the instrument must agree with the
address specified in the controller’s program.

To check the present address. or to enter a nc~ one.

proceed as follows:

IEEE C’ontncf Designo~im.

Data
Data
Data
Data

Management
Handshake
Handshake
Handshake
Management

SRQ

Management
Management
Ground
Data
Data
Data
Data
Management
Ground
Ground
Ground
Ground
Ground
Ground

LOGIC Ground

GPIB Address

NOTE

The programmed primary address is

briefly displayed during the power-

up cycle of the Model 776. It is
stored in the non-volatile memory of
the instrument and is retained even
when power is turned off.

IEEE-488 Operntion

1. Press the 2nd push-button once then press the ADR
push-button (second function to SLOPE). The display
will be modified to display the following:

1. Uniline commands: Sent by setting the associated bus

line low.

2. Multiline commands: General bus commands which
arc sent over the data lines with the ATN lint low (true).

IE Adr x

Where s may be any number from 0 to 30

3. Device-dependent commands: Special commands
that depend on dcvicc configuration: sent oycr the data

lines with ATN high (false).

2. Press the VERNIER fi or u push-buttons the select a
new GPIB primav address.

4-8-l Uniline Commands

Uniline commands are sent by setting the associated bus

3. To store the newly selected primary address depress
ENT (second function to STO). The instrument a-ill then
resume normal operation,

line to 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 controlleroran external device
depending on the direction of data transfer. The follow-

4-8. Bus Commands

While the hardware aspect of the bus is essential. the

ing is description of each command.

REN

(Remote Enable) - The rcmotc cnablc command is
interface would be essentially worthless without appro- sent to the Model 776 by lhe controller to set the instru­priate commands to control the communications be-

ment up for remote operation Generally. this should bc
tween the various instruments on the bus. This para- done before attempting to program the instrument over
graph briefly describes the purpose of the bus com- the bus. The Model 776 will indicate that it is in the
mands. which are grouped into the following three cate- remote mode by illuminating its front panel REM indi-

cator.

r

COMMAND COMMAND STATE OF COMMENTS
TYPE ATN LINE(*)

Uniline

REN

X

Set up for remote operation
EOI X Sent by setting EOI Ion
IFC
ATN

SRQ

Multiline Universal

LLO
DCL
SPE
SPD
SDC

GTL

~~.~~-. -.~.~-~GET.~

Unaddress UNL

UNT

Device- Dependent(**)

X Clears Interface
LO\\ Dcfincs data bus contents
X~ Controlled by~~external de\,icc

Lon
LO\\

Locks out front panel controls

Returns device to default conditions
Loa Enable serial polling
LOI\

Disables serial polling Addressed
Lou Returns unit to default condition
LO\%

.,,!m

Len
LO\\

High

Returns to local control

Tiggq device. for mading

Removes all listeners from bus

Removes all talkers from bus

Programs Model 60.10 for various modes.

(*I X = Don‘t Care. l**) See paragraph .l-9 for complete description

1-6

IEEE-488 Operolion

To place the Model

776

in the remote mode. the

controller must perform the following steps:

1. Set the REN line true.

2. Address the Model

776

NOTE

to listen.

Setting REN true without addressing
will not cause the REM indicator to
turn on: however. once REN is true,
the REM light will turn on the next
time an address command is re­ceived.

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.

IFC

(Interface Clear) - The IFC command is sent to

clear the bus and set the Model

776

to a known state.
Table 4-4 summarizes the instrumeut’s state after IFC
OT DCL. Although device configurations differ. the IFC
command usually places instruments in the talk aud
listen idle states.

ATN

(Attention) - The coutroller sends ATN while

transmitting addresses or multiline commands. Device-

dependent commands are sent with the ATN line high

(false).

SRQ

(Service Request) - The SRQ command is as-

serted by an external device when it requires sen:ice

from the controller. If more thau one device is present.
a serial polling sequence. as described in paragraph
4-8-2, must be used to determine which has requested
setvice.

4-8-2. Universai multiline 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 liues with ATN set low:

LLO

(Local Lockout) - The LLO comtuaud is seut b)
the controller to remove the Model 776 from the local
operating mode. Once the unit receives the LLO com-

mand. all its front panel controls (except Power) will be
inoperative.

NOTE

The REN bus liue must be true before
the instrument will respond to an
LLO command.

To lock out the frout panel controls of the Model

776.

the controller must perform the following steps:

1. Set ATN true.

2. Send the LLO command to the instrument.

DCL

(Device Clear) - The DCL command may bc used
to clear the Model 776. setting it to a known stale. Note
that all devices on the bus equipped to respoud to a DCL
will do so simultaneously. When the Model

776

receives
a DCL command. it will return to the default conditions
listed in Table 4-4.

To send a DCL command the coutroller must per-

form the followiug steps:

1. Set ATN tie.

2. Place the DCL command on the bus.

SPE

(Serial Poll Enable) - The serial polling sequence

is used to obtaiu the Model

776

status byte. Usually. the
serial polliug sequence is used IO determine which of
several devices has requested service over the SRQ line.
However. the serial polling sequeuce may be used at any
time to obtaiu the status byte from the Model 776. For
more iufonnation on status byte format. refer to para-

graph 4-9-20. The serial polling sequence is conducted
as follows:

1. The controller sets the ATN line true.

2. The SPE (Serial Poll Enable) commaud is placed on
the bus by the controller.

3. The Model 776 is addressed to talk.

4. The controller sets ATN false.

5. The Model 776 then places its status byte ou lhe bus
to be read by the controller.

6. The controller then sets the ATN liue low aud places
SPD (Serial Poll Disable) ou the bus to cud the serial

polling sequence.

Steps 3 trough 5 may be rcpcated for other instru-

ments on the bus by using the correct talk address for

each instrument. ATN must be true when the talk ad­dress is trausmitted and false when the slams byte is

read.

SPD

(Serial Poll Disable) - The SPD command is sent
by the controller to remove all instnunenlatiou ou the
bus from the serial poll mode.

4-8-3. Addressed Commands

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

4-7

IEEE-488 Operation

SDC (Selective Device Clear) - The SDC command
performs essentially the same function as the DCL com­hand except that bnly the addressed device will re­spond. This command is useful for clearing only a se­lected instrument instead of all devices simultaneously.

The Model 776 will return to the default coudilious

listed in Table J-4 when responding to au SDC com­mand.

To transmit the SDC command. the controller must

perform the following steps:

1. Set ATN true.

2. Address the Model 776 to listen.

3. Place the SDC command on the data bus.

GTL

(Go To Local) - The GTL command is used 10
remove the instrument from the remote mode of opera­tion. Also: front panel control operation will usually be

Table 4-4.

Default Condifiom @lotus After SDC or DCLi

restored if the LLO command was previously seul. TO
send the GTL command. the controller must perform

the

following sequence:

1. Set ATN tme.

2. Address the Model 776 to lislcu.

3. Place the GTL command ou the bus

NOTE

The GTL command does not remove
the local lockout state. With the local
lockout condition previously set. the
GTL command will enable front
panel control operation until the nest
time a listeuer address command is
received. This places the Model 776

in the local lockout state again.

Function
Coupling
Attenuator
Filter

Slope
lmpedauce
Coupling

Attenuator
Filter

Slope
lmpedauce

Auto Trigger
Dela)
V Peak Rate
Totalize Mode
Ratio Mode
Displayed Digits
Rate
SRQ mask
Terminator
Display mode
Data format
Trigger level
Trigger level

Gate time
Delay time

FO

AC0

AA0

AFO
AS0
A10
BCO
BAO
BFO
BSO

BIO
LO

IO
vo

MO

co

NIO
&

zo

DO
X0
AL0
BLO
Gl
WI

Frequency A
DC coupled on channel A.

xl attenuator on channel A.

Filter off ou channel A.

Positive slope on chanuel A.

1 MR on channel A.
DC coupled on channel B.
xl atteuuator on channel B.
Filter off ou channel B.
Positive slope on channel B.

I MC> on channel B.
Manual trigger disabled.
Delay disabled.
Fas1 measurement rate.
Totalize iufiuitely.
Ratio A/B.
Set maximum displayed digits to 10.
Normal 3 readings per second.
SRQ disabled.
CR LF with EOI.
Display 1he measurement.
prefix on. no leading zeros.
OV on chauncl A.
OV on channel B.

I second gate time.

1 second delay time.

4-8

IEEE-488 Operntion

GET (Group Execute Trigger) - The GET command is
used to trigger or arm devices to perform a specific
measurement that depends on device configuration. Al­though GET is considered to be an addressed command.
many devices respond to GET without being addressed.
Using the GETcommand is only one of several methods

that can be used to initiate a measurement cycle. More
detailed information on triggering can be found in Sec­tion 3 of this manual.

To send GET command over the bus. the controller must
perform the following sequence

1. Set ATN true.

2. Address the Model 776 to listen.

3. Place the GET command on the data bus.

GET can also be sent without addressing by omitting
step 2.

4-94. Unaddress Command

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

UNL (Unlisten) -All listeners arc removed from the bus
at once when the UNL commands is placed on the bus.
UNT (Untalk) - The controller sends the UNT command
to clear the bus of an)- talkers.

ASCII characters (00 HEX through 20 HEX) escepl lhe

“CR” (carriage return). A command string is terminated
by an ASCII “CR” (carriage return) character (OD HEX)
which tells the instrument to cxecutc the command

string. recognized as end of command string.

If an illegal commaud or command paramelcr is

present within a command string. the instrument will:

1. Ignore the entire string.

2. Display appropriate front panel error message.

3. Se1 certain bits in its status byte.

4. Generate an SRQ if programmed to do so.

These programming aspects arc covered in tbc fol-

lowing.

NOTE

Before performing a programming
example. it is recommended that the
instrument be set to its default values

by seuding an SDC over the bus.

In order to send a device-dependent command. the

controller must perform the following sequence:

1. Set ATN true.

2. Address the Model 776 to listen

3. Set ATN false.

4. Send the command string over the data bus one byte
at a time.

NOTE

4-9-5. Device-Dependent Commands

The meaning of the device-dependent commands is de­termined by instrumeut configuration. Generally. these
commands are seut as one or more ASCII characters that
tell the device to perform a specific function For esam­ple. FO is sent to the Model 776 to place the instrument
in the FREQ A mode. The IEEE-488 bus treats device­dependent commands as data in that ATN is high (false)
when the commands are transmitted.

IEEE-188 device-dependent commands are sent to
the Model 776 to control various operating conditions
such as display modify. operating mode. output and
parameter insertion. Each command is made up of an
ASCII alpha character followed by one ormore numbers
designating specific parameters. Foresample the output

waveform is programmed by send@ an ASCII “U”

followedby a number representing the output. The IEEE
bus treats device-dependent commauds as data in that
ATN is high when the commauds are transmitted.

A number of commands may be grouped together in

one string. The Model 776 will ignore all non-printable

REN must be true when attempting lo
program the Model 776.

Commands that effect the Model 776 arc listed in

Table 4-S.

4-9. Device Dependent Commands

Programming

4-9-l. Function (F)

The function command sclecc the type of mcasurcnlcnt

made by the Model 776. The 13 parameters. which arc
associated with the function command. set the instru­ment to measure one of these functions. The functiou
may be programmed by sending one of the following
commands:

FO=FRQA

Fl=FRQB
FZ=FRQC
F3=PERA
FJ = PLS A
FS = TI A to B

4-Y

IEEE-188 Operation

Table

4-5. Device-Dependent Coirrnrond Sunrfmry

Function

I

Coupling

Attenuator

Filter

-.

FO
Fl

Frequency on Channel A

Frequency on Channel B
F2 Frequency on Channel C
F3

Period on Channel A
FJ Pulse on Channel A
F5

Time interval from A to B
F6 Totalize on B
F7

Ratio FRQ/B (see also Ratio Mode)
FS Phase A to B
F9 V peak A
FlO

Period average on Channel A
Fll Pulse average on Channel A
F12

AC0
AC1

BCO

Time_i~!g&from.~& ~.&!_v~!WZ~~ ~.~ ..~._

DC coupled on Channel A

AC coupled on Channel A
DC coupled on Channel B

.._. ~~~~ .,,_. ~.~_~~

g.q _ _, __.-._ AC ~o~~edon~Chalme!.B. ~~~~~~~ ~~~ ..,, ~~.~ ~~~~~ ~~~~~ .,.. ~. ~- ..,,-. ~~~~~ ~~~

AA0
AA1
BAO

XI attenuator on Channel A
X10 attenuator on Channel A
Xl attenuator on Channel B

BAI X10 attenwtg onC!lgan!lc! Ej

AFO Filter Off on Channel A
AFl
BFO
BFI

Filter On on Channel A
Filter Off on Channel B

Filter On ~011 Channel B .~. ~_~~~ .~~~ .._ ~.~~.

~-~~-~~.-.,.-~.-

Slope

Impedance

Trigger level

Auto level

4-10

AS0
ASI

Positive Slope on Channel A
Negative Slope on Channel A

BSO Positive Slope on Channel B

__, .SS! .,., ..~ ,~.. ..Yesative S!oI?e p_. Channel US .~-~

AI0 1 Ma impedance on Channel A
AI1
BIO
BII

50 n impedance on Channel A

1 Mn impedance on Channel B

m-~_son.i,3~peclance~ on_~Channel !? ~., ..~~~

AL”
BLn

LO

LI

Auto trigger level disabled
Auto trigger level enabled (mode overrides manual mode)

...~~~~~ ~.

c

F6=TOTB
F7 = RATIO FRQIB

FE

= Phase A to B

F9 = V peak A

FlO

= PER AVG A

Fll = PLS AVG A

F12 =

TI A to B AVG

4-9-2. Channels A, 6 Coupling (AC, BC)

The coupling commands give the user control over the
input coupling of Channels A and B inputs. Coupling
may be programmed by sending one of the following
commands:

AC0

= DC coupling channel A.

J-11

AC1 = AC coupling channel A.

BCO = DC coupling channel B.
BCl = AC coupling channel B.

4-9-3. Channels A, B Attenuator (AA, BA)

The attenuator commands give the user control over the

input attenuator mode of channels A and B. The attenu-

ator may be programmed by sending one of the follow-

ing commands:

AA0 = xl attenuator channel A.
AA1 = xl0 attenuator channel A.
BAO

= xl attenuator channel

BAI = x10 attenuator channel B.

B.

The trigger level may be programmed by sending one of
the following commands:

ALn = Trigger lewl channel A.
BLn = Trigger level channel B.

n is the trigger level in units of volts and in cnginccr-

ing format: e.g. (fD.DDiD). The sign and the csponcnt
are optional. The trigger level value may range from

-5.00 to +5.00 V in IO mV increments or from -50.0 to

+50.0 V in IOOmV incrcmenls. Selecting trigger Icvcl
wilbin the range of *S.OO V. automatically scls the

attenuator to xl. Selecting a trigger level within the

range of *SO.0 V. automatically modifies attenuator

selling to x10.

4-94. Channels A, B Filter (AF, SF)

The filter commands give the user control over the filter
at Channels A and B input. The filter may be pro­grammed by sending one of the following commands:

AFO = filter on channel A.
AFl = filter off channel A.
BFO = filter on channel B.
BFl = filter off channel B.

4-95. Channels A, B Slope (AS, BS)

The slope selection commands give the user control
over triggering edge at channels A and B inputs. The

slope may be programmed by sending one of the follow­ing commands:

AS0 = Positive slope channel A.
AS1 = Negative slope channel A.

BSO = Positive slope channel B.
BSl = Negative slope channel B.

4-9-9. Channels A, B Impedance (Al, Bl)

The impedance selection commands give the user con­trol over the input impedance at channels A and B
inputs. The impedance may be programmed b?; sending
one of the following commands:

AI0

= 1

MQ

impedance channel A.

AI1

= 50 R impedance channel A.

BIO = I MQ
BIl

= 50 22 impedance channel B.

impedance channel 8.

Following DCL or SDC commands. the instrument

defaults to ALO and BLO (trigger levels set to 0.00 V).

4-9-9. Channels A, B Auto trigger level (L)

The auto trigger level commands give the user control
over the auto trigger level mode. Auto-trigger mode is
automatically selected for both Channels A and B. The
aulo-trigger level mode may be programmed by sending
one of the following commands:

LO = Auto-trigger level disabled.
Ll = Auto-trigger level enabled.

4-98. Gate lime (G, GU)

The gate lime commands control the time that the gate
remains open. The gate time may be programmed by
sending command strings using the following formats:

Gnn = Internal gate time
GU = External user gate time

nn is the gate time in units of seconds and in engi­neering format. e.g. (D.DE+D). Sign. decimal point. sod
exponent are optiooal.

The operator has the option or selecting an external
gate time having periods other then those programmed
into the instrument. The counter may be programmed to

accepl external gate times by sending the GU command
over the bus.

Following DCL or SDC. the instrument defaults to

gate time oi one second (G I .O).

4-9-7. Channels A, B Trigger Level (AL, BL)

The trigger level commands give the user control over
the trigger threshold point at channels A and B inputs.

J-12

4-g-10. Delay Time (IV, WU)

The delay time commands control the delay in closing
the gate after the gate was open. The delay time may be

programmed by sending commands using the following
formats:

Wnn

= Internal delay time.

WU = External user delay time.

nn is the delay time in units of and seconds in
engineering notations: e.g. (D.DE*D). Sign. decimal
points, and exponent are optional.

The operator has the option of selecting an external
delay time having periods other than those programmed
into the instrument. Model 776 may be programmed to
accept external delay times by sending the GU com­mand over the bus.

Following DCL or SDC. the instrument defaults to

delay time of one second (W1.0).

4-9-14. Displayed Digits (N)

The displayed digits function sets the maximum number
of digits that the Model 776 will display. To program
the number of digits send the following command:

N”

Where n may have any value from 3 to IO. Upon

DCL or SDC. the instrument will be set IO NIO.

4-9-15. Set-ups (ST, RE)

The setups commands select the memory location whcrc
the actual set-up is to be stored at (ST). or recalled from
(RE). To store or recall a front panel set-up use one of
the following commands:

4-9-11. V Peak Measurement Rate (V)

The V peak measurement rate commands control the
rate of which the instrument performs its v peak meas­urements. Model 776 offers a choice of two measure­ment rates: Fast, and slow. The fast rate is normally used

when measuring amplitudes of a signal having frequen­cies from 100 Hz. The slow rate is used when perform­ing measurements below IO0 Hz. The v peak measure­ment rate may be programmed by sending a command

using the following formats:

VO

= Fast measurement rate.

Vl = Slow measurement rate.

4-9-12. Totalize Modes (M)

Model 776 offers three gating options for its Totalizc
mode. They are: Gate is open infinitely. Gated by A. and
Gated by AA. The totalize mode commands give the
user control over the selection of one of these gating
options. The totalize mode may be programmed by
sending command strings using the following format:

MO = Totalize on B. gate open infinitely.
Ml = Totalize on B. gated by A.
MZ = Totalize on B. @ted by AA.

4-9-13. Ratio Mode (C)

The Ratio Mode commands operate in conjunction with
the F7 command (FRQ/B). These commands control the
input to be divided by the B Channel input. The ratio
mode may be programmed by sending command strings
using the following format:

CO = Ratio measurement. Crcquency A/E.
Cl = Ratio measurement. frequency C/B.

STll
REn

n designates a specific mcmo~ address. and ma!
range fro”, 0 to 9. DCL or SDC has no effccl
stored set-ups.

on

the

4-9-16. Triggering (T)

The “T” and GET commands are used to trigger the
Model 776 over the IEEE bus. Triggering command
arms the counter for a fresh measurement c!;clc. In its
continuous mode. Model 776 is always armed. while in
its hold mode (SO). a separate trigger stimulant is re-

quired lo arm for a new n~casurcment cycle. To arm the

Model 776 for a new measurement cycle use the follou­ing commands:

T = Addressable trigger.

GET

= Group Esecutc Trigger.

4-9-17. Rate (S)

The rate commands give the user control over the speed
that Model 776 oulpuls its processed measurements on
the bus. Model 776 may output up to 100 formatted
readings in one second. Such speed. however. requires
that either S2 or S3 rates are selected. that the pro­grammed gate time is less than IO ms. and that unnec­essary information such as prefixes. and leading spaces
are removed from the output string. Also when selecting
one of the fast rates. now that there arc frequency limits
which are associated with each rate mode. SO and S I

may be seleclcd from the front panel. SZ and SR can only

be programmed from the GPIB. The various speed rates

may be programmed using one of the following corn­“lands:

J-13

SO = Hold. One shot on T. or on GET. or on an external

arming input.

Sl = Normal. Approsimatel~ 3 reading per second.
S2 = Fast, up to 100 reading per second. 100 Hz to 120

MHz.

S3 = Fast. up to 100 reading per second. IO MHz to 225

MHz.

4-9-18. Display Modes (D)

The display command controls what parameter the
Model 776 will place on the display. The eight parame­ters associated with the display commands set the in­strument to display the normal measurement. gate time.
delay time, trigger level A, trigger level B. number of
selected digits, analog output resolution. analog output
offset. and ratio mode. The counter may be programmed
to place one of the above parameters on the display
using the following commands:

DO = Display the normal measurement.
Dl = Display the gate time.
D2 = Display the delay time.
D3 = Display the A trigger level.
D4 = Display the B trigger level.
DS = Display the number of digits.
D6 = Display the analog output resolution.
D7 = Display the analog output offset.
D8 = Display the programmed ratio mode.

4-9-19. SRQ Mode (Q) and Serial Poll

Status Byte Format

The SRQ command controls which of a number of
conditions within the Model 776 will cause the instru­ment to request service from the controller with the SRQ
line command. Once the SRQ is generated. the Model
776 status,bTte can be checked. via serial pollingY to
determine if it was the Model 776 that requested service.
Other bits in the status byte could also be set depending
on certain data or error conditions. The Model 776 can
be programmed to generate SRQ under one of the fol­lowing conditions.

1. If the Model 776 is ready to receive device-dependent
commands.

2. If a reading has been completed.

3. If an error condition has occurred.

bits. Table J-6 lists the commands to set the various
mask bits. while Table 4-7 lists all legal SRQ Mask
commands.

NOTE

There arc 8 legal SRQ mask com-

mands that are possible with the

Model 776. Table 4-7 lists all combi-

nations. e.g selecting 46. Model 776

will request service when one of

reading done or error occurs.

Status Byte Format:

The status byte contains informa-

tion relating to data and error conditions within the

instrument. Table 4-8 lists the mcaning of the various
bits. The status byte is obtained by using the SPE. SPD
polling sequence.

The various bits in the status byte are described below:

1. Ready:

the Model 776 receives a command and set again

Set after power-up. This bit is cleared when

wllell

the instrument have completed to decode the command
(Model 776 is ready for the next command string).

2. Reading done:

Set after completion of a measurc­ment cycle. The reading done bit is cleared after Model
776 was addressed to talk in RO mode.

3.

Error:

Set if an illegal command has been received
or one of gate error. gate time error. ortrigger level error
has occurred in the last measurement cycle. This bit is
cleared by reading the error status string (R7).

4.Rqs (request service):

Model 776 sets this bit if one

or more conditions for service request occur. and the

SRQ mask. for at least one of these service requesl

conditions is enabled. This bit is cleared by reading the

Status Byte using the SPE. SPD polling sequence.

NOTES

1. Once the Model 776 has generated an SRQ. its stalus

byte should be read to clear the SRQ line. Othew:isc the

instrument will continuously assert the SRQ line.

2. The Model 776 may be programmed to generate an
SRQ for more than one condition simultaneously. For
example. to set SRQ mask bits for an SRQ if an error
occurs and when the instrument is ready for the ncsl
string. the following command would be sent: QS. All
possible mask combinations are listed in Table 4-7.

SRQ Mask:

In order to facilitate SRQ programming.
the Model 776 uses an internal mask to generate the
SRQ. Whena particular mask bit is set. Model 776 seods
an SRQ when those conditions occur. Bits within the
mask can be controlled by sending the ASCII letter “Q”
followed by a decimal number to set the appropriate

4-14

3. If the instrument is programmed to generate an SRQ
when reading is done, it will generate the SRQ only once
when the reading is complctc: the SRQ may be cleared
by reading the status byte. The reading done bit in the

slatus byte may then be cleared by rcquestiog a normal
reading from the instrument (RO).

4-10. Reading From Model 776

The Reading sequence is used to obtain from Model

776. various information strings such as measurement.
gate time, delay time or trigger level. Each information
string is made up of ASCII alpha and alphanumeric
characters. For more details on the information strings
format refer to paragraph 4-10-I.

Table 4-9 shows the general data string format for each
of the seven commands (decimal point floats).

Table 4-10 shows the interpretation for the input condi­tioning status. operating mode status and error status
strings (RS. R6 and R7).

NOTES

The reading sequence is conducted as follows:

1. The controller sets the ATN line true.

2. The Model 776 is addressed to talk.

3. The controller sets ATN false.

4. The instrument sends the information string over the
bus one byte at a time.

5. The controller recognizes that the string is termi­nated.

6. The controller sets the ATN line true.

7. The UNT (untalk) command is placed on the bus b)
the controller.

NOTE

Most controllers use the CR (Car­riage Return) orLF (Line Feed) char­acter to terminate their input se­quences. but other techniques may be
used as well to recognize the end of
input sequence (for example the EOI
line is low on the bus during the
transfer of the last byte).

4-10-I Data Control commands (R)

The Data Control commands allows access to informa­tion concerning present operating conditions of the in­strument. When a data control command other than RO)
is given. the Model 776 transmits the associated data
string instead of its normal data string.

it is

addressed to talk,

normal measurement data string (RO).

Model 776 will transmit its

Model 776 defaults to RO state. It is therefore not nec­essary to include the RO command in every reading

request.

The Model 776 Data Control commands include:

RO

= Send normal measuring data string

Rl

= Send Gate Time data status string

R2 = Send Delay Time data status string

R3 = Send Trigger Level A data status string

RJ

= Send Trigger Level B data status string

RS

= Send Input conditioning status string

R6 = Send Operating Mode Status string

R7 = Send Error Status string

The next

Note that

time

1. Data strings have fixed length of 15 ASCII characters
for the RO. RS and R6 commands without the prefix and
terminator. For all other data strings (RI through R4 and
R7). the length of the data string is 5 ASCII characters

without the prefix and terminator. If the data string is

sent with a prefix. four additional ASCII characters arc
included (refer to paragraph 4-2-3). If the data string is
sent with one or two terminators. the length of the data
string increases by one or two characters respectively.

2. All normal measurement data string information
(RO). besides the status strings (RI through R7). will be
sent only once each time a measurement has been suc­cessfully completed. This may halt the controller for the
duration of the gate or delay time. It is therefore rccom­mended that the status byte will bc continuously moni­tored and normal reading taken only after the READ­ING DONE bit is set true.

WARNING

Model 776 updates its GPIB

huff-

ers only once at the end of a SUE-

cessful measurement cycle. If a
normal reading is requested before
the gate is closed, the bus could be
held for, at least, the duration of
the gate time. With some control­lers, this delay may cause control­ler time-out, or even a complete
bus lockup. It is therefore recom­mended that the Model 776 is pro­grammed to assert an RQS on
Reading Done (Q2). and that a nor­mal reading is requested only if the
Reading Done bit (Bl) in the status
byte is set. The procedure of rcad­ing the Status Byte, as well as its
interpretation, is given in paw­graph A-9-21.

3. All status string information. besides the normal data
strings. will be sent only once each time the command
is sent. Once the data string is read. the instrument will
send its normal data string (RO) the next time it is
addressed to talk. CR LF is normal tcrminatoc The

J-15

IEEE-488 Operation

Table 4-7.

Bit Number B2 Bl

Command Error Done_

terminator may be changed

SRQ Mask Legal Co~nrnnnds

Reading

NO NO

zf
:i

Q4

::

Q7

NO NO
NO YES
NO YES
YES NO NO

YES NO YES
YES YES NO
YES YES YES

(see paragraph J-10-2). The

BO (LSB)
Ready

NO
YES
NO
YES

prefixes are listed in Table 4-9.

NOTES

1. The Error Status string will be returned only once
each time the command is sent. Once &xus is read. the
instrument will send its normal swing the next time the
instrument is addressed to talk and reading done bit is
set true.

2. To ensure that the correct status is received. the status
string should be read immediately after sending the
command. to avoid having an incorrect status transmit­ted.

3. The status string should not be confused with the
status byte. The status string comains a string of bytes

pertaining to the various operating modes of the instro-

mew. The status byte is a single byte hat is read wilh

the SPE. SPD command sequence and contains informa­tion on SRQ status.

4. The error status string is cleared by reading R7.
Reading this status also clears the reading done and lhe
error bits in the status byte.

4-l O-2. Terminator (2)

To allow a wide variety of controllers to be used. the
terminator can be changed by sending an appropriate
command over the bus. The default value is the com­monly used carriage return, line feed (CR LF) sequence
(mode ZO). The terminalor sequence will assume this
default value after receiving a DCL or SDC.

The EOI line on the bus is usually set low by the

device during the last byte of its data transfer sequence.

In this way. the last byte is properly identified. allowing

variable length data words to be transmitted. The Model

776 will normally send EOl during the last byte of its
data string or status word. The terminator and the EOI
response from the Model 776 ma\ be sent with one of
the following commands:

ZO

= CR.LF with EOI

Zl

= CR.LF wilbout EOI

Z2

= LECR with EOI
23 = LF.CR without EOI
24 = CR with EOI

ZS

= CR without EOI

26 = LF with EOI

27

= LF without EOI

2% = No terminator with EOI

Z9

= No terminator without EOl

Table 4-8. Stntus Bvfe

Interpretation

4-16

Inferprcmtion

0

“7s

0 0

0

Reading

Error Done Ready

Table 4-9.

Data String Formats

~-ccqmand

RO

Data String~Ponnat

(FRQA)+l.231567890E+O(TERM)
(FRQB)+l.23~S6789OE+O(TERM) for FRQ B “,eas”rc”~c”ts

(FRQC)+l.234.567890E+O(TERM) for FRQ C measurements
(PERS)+l.23456789OE+(‘IERM)
(PLSS)+l,234567890E+(TERM) for PLS A measurements
(TABS)+l.23~567890E+O(TERM)
(TOTB)+l.234567890E+O(TERM)
(ATOB)+l,234567890E+O(TERM) for Ratio A/B measurements
(CTOB)+l.234567890E+O(TERM)
(PHAS)+l,234567890E+O(TERM)
(VPKA)-O.OO -0.00 (TERM) for V PeaK A measureme”ts
(PERV)+l.23456789OE+O(TERM) for PER AVG A measurements
(PLS V)+l.23-+567890E+O(TERM) for PLS AVG measurelnents
(TABV)+I,234567890E+O(TERM) for T.1 A to B AVG measurements

RI
P.2
R3
R4
R5
R6
Rl

1.

Most co”trollers “se the CR or LF character to termi-

(GATE)lOE-O(TERM) for Gate Time
(DLAY)lOE-O(TERh4) for Delay Time
(TRGA)+O.OO(TERM) for Trig Level A
(TRGB)+O.OO(?ERM)
(STAT)OOOOOOOOOOOoOOO(TERM) Input conditioning status
(776)000001000100000(TERM)
(EROR)OOOOO(TERM) Error status

NOTES

“ate their input sequence. Using the NO TERMINATOR
mode (28 or Z9) ma); cause the controller to hang up
unless special programming is used.

2. Some controllers may require that EOI be present at

the end of transmitting.

4-103. Prefix (X)

The prefix from the data string may be suppressed “sing
this command. When the prefix is suppressed the output

~~, ~~Deuc,rM!9c ~~..-. ~~~

for FRQ A meas~rcm~nts

for PER A measurements
for T.1 A to B measurements

for TOT B measurelnents
for Ratio C/B measurements

for Phase A to B mcasuwments

for Trig Level B
Machine status

data string is four byte shorter. The X command is also
used to replace leading space character(ASCIl2() HEX)

in the data string with character 0 (ASCII 30 HEX). For
some controllers. a” attenlpl to wad a number instead of
a string, will result a reading error because of its inabil­ity to read spaces before the first significant digit. To
eliminate this problem the Model 776 should bc pro-

arammed to send the data string with leading zeros. X4
mode is an absolute necessity to reach the readiog speed
of “p to 100 readings per second (in col~junction nil11

S2 and S3). X command parameters include:

Table 4-10. ,Slntrrs IIbrci’

Command

R5

After SDC

R6

After SDC

R7

After SDC

Inlerpr~lniion

.., ..~~$tatus ~J@r$~~ormat

(STAT) F AC AA AF AS AI BC BA BF tiS Bl L 1 O(tcrm)

(STAT)00 0 0 0 0 0 0 0 0 0 0 0 0 O(CR LF)

(776) OPTI OPT2 OPT3 V M C N 0 P S Q Z D X(terml
(776) n n n

o o o IO 0 o 1 0 0 0 O(CR LF)

(EROR) IL1 ILP GATEERR TLERR 0 (CRLF)
(EROR) 0 0 0 0 0 (CR LF)

1-17

X0 = Send data string with prefix. without leading
zeroes.
X1 = Send data string without prefix without leading
zeroes.
X2 = Send data string with prefix. with leading zeroes.
X3 = Send data string without prefix. with leading
zeroes.
X4 = Send data string without prefix. without leading
zeroes, without leading spaces.

4-11. Front Panel Error Messages

2. Set appropriate bits in the status byte and error word.

3. Generate an SRQ if programmed to do so.

4. Display an appropriate front panel mcssagc.

4-WI. ILL INS (Illegal Instruction) Error

An ILL INS error results when the Model 776 rccewx

an invalid command such as AO. This command is inva-

lid because no such letter exist in the instrumcnls pro-

gramming language.

The process of programming the Model 176 involves
the properuse of syntax. Syntax is defined as the orderly
or systematic arrangement of programming commands
or languages. The Model 776 must receive valid com­mands with proper syntax or it will:

1. Ignore the entire commands string in which the inva-

lid command appears.

4-11-2. ILL PAR (illegal Parameter) Error

An ILL PAR error occurs when the numeric paramelcr
associaled with a legal command lctter is invalid. For
example_ the command D 10 has an invalid oplion be­cause the Model 776 has no display mode associated
with that number.

4-18

5

Maintenance and

Performance Tests

5-I. Introduction

This section provides maintenance. sewice information.
and performance tests for the Model 776. the clock

multiplier and the 2.4 GHz input channel. Fuse replacc­ment procedure and line voltage selection arc also in-

cluded.

WARNING

The procedures described in this sec­tion are for use only by qualified
service persomlel. Do not perform
these procedures unless qualified to
do so. Many of the steps covered in
this sectibn may expose the individ­ual to potentially lethal voltages that
could result in personal injuv or
death if normal safet? precautions
are not observed.

5-2. Line Voltage Selection

The Model 776 may be operated from either 1 IS V or

230 V nominal SO-60 Hz power sources. The instrument

was shipped from the factov set for an operating volt-

age as advised on your purchase order. To change the
line voltage. proceed as follows:

1. Using a flat-blade screwdriver. place the lint voltage
selection switch in the desired position. The voltages
are marked on the selection switch

2. Install a power line fuse consistent with the operating
\:oltagc. See paragraph S-3.

CAUTION

The correct fuse type must be used to
maintain proper mstrument protec­tion

53. Fuse Replacement

The Model 776 has a line fuse to protect the instrument

from excessive current. This fuse may be replaced by
using the procedure dcscribcd in the folloning:

WARNING

Disconnect the instrument from the
power lint and from other equipment
before replacing the fuse.

1. Place the cod of a flat-blade screwdriver into the slot

in the LINE FUSE holder on the rear panel. Push in and
rotate the fuse carrier one quarter turn counterclock-

WARNING

Disconnect the Model 776 from the
power cord and all other sources be­fore changing line voltage setting.

i-l

wise. Release the pressure on the holder and let its
internal spring to push the fuse and the carrier out of the
holder.

The counters fcaturc a rear panel input/output BNC

connector designated as 10 MHz CLOCK OUT/EXT

CLOCK IN. This wnncctor sewes Iwo functions:

2. Remove the fuse and replace it with the proper type
using Table 5-1 as a guide.

CAUTION

Do not use a fuse with a rating higher
than specified or instrumem damage
may occur. If the instrumcnc persist­ently blows fuses. a problem may
exist within the instrument. If so. the
problem must be rectified before
continuing operation.

54. Selecting an External Frequency
Reference

The Model 776 has a 5 PPM oscillator for an internal
time base clock. The Model 77612.46 and 776/2.4G/R
have TCXO (temperature compensated cryslal oscilla­tor) included with Channel C option.

Thcsc time bases are enough to satisfy most accurac)

requirements: however. in applications where such an
inaccuracy is a limiting factor. an external standard can
be applied to the counters. The basic accuracy of the
counters is then converted to the accuracy of the applied
frequency source.

The Model 776 accepts a 10 MHz source: the Model

7762.46 and 776/2.4G/R accepts a 5 MHz or IO MHz
SOUTCIZ

.

When an internal clock is selected. a 10 MHz signal
from the internal time base circuit is available al
this output.

.

While using the instrument wilh an external refcr­ewe. a signal is applied to the same connector.

The counters arc shipped set to operalc with an

internal time base. and wilh a IO MHz signal available
at the rear panel CLOCK output. To change these set­tings. refer to the following procedure:

WARNING

Disconnect the line cord and test

leads from the instrument before re-

moving the top cover.

1. Removc the top cowr as described in the disasscmbl)

instructions in paragraph S-S.

2. Position the shorting links as required:

A. For Models 77612.46 and 776/2,4G/R. refer to

Figure 5-l for the shorting link locations on the TCXO

board. LKl and LK2 sclcct the internal or e.xlcrnal

reference. LK3 configures the instrument for a 5 MHz

or 10 MHz external reference.

B. For a Model 776. refer to Figure S-2 for shorting
link locations on the main board. LKI (a and b). which
is located at the rear of the instrument near the poewr
transformer. selects the internal or eslernal reference.

3. Replace the top cover.

5-2

!#jl$j -oaLl

Internal

EXternal

5MHz 1OMHz

/-Locking Screw

$7

Ul

TCXO-26A 0

\

0

5-5. Disassembly Instructions

If it is necessary to troubleshoot the ins1rument or re­place a component. use the following disassembly pro­cedure to remo\:e the top and bottom covers:

1. Remove the four screws that secure each of the top

and the bottom covers.

2. Grasp 1he top cover al the side and carefully Iif1 it off
the instrument. Similarly remove the bottom cover.

3. When replacing the covers. reverse the above proce­dure.

2. Remove the devices from 1hc protective containers
only at a properly grounded work slation Also ground
yourself with a suitable wrist strap.

3. Remove the dwiccs only by the body: do not touch
the pins.

4. Any printed circuil board in1o which the device is to
be inserted must also bc grounded 10 the bench or table.

5. Use only anti-static type solder sucker.

6. Use only grounded soldering irons.

7. Once the device is installed on the PC board. the

device is normally adcquatcly protected. and normal

handling rcsumc.

5-6. Special Handling of Static

Sensitive Devices

CMOS devices are designed to operate at a very high
impedance levels for low power consumption As a
result. any normal stalic charge that builds up on your

person or clothing may be sufficient to deslroy these
devices if they are not handled properly. When handling
such devices. use precautions which are described in the
following to avoid damaging them.

1. The CMOS ICs should be transported and handled
only in containers specially designed to prevent static

build-up. Typically. these parts will be received in

static-protected containers of plastic or foam. Keep

these devices in their original containers until ready for

installation.

5-7. Cleaning

Model 776 should bc cleaned as often as operating
condition require. Thoroughly clean the inside and the
outside of the instrument. Remove dust from inaccessi-

ble areas with lov pressure compressed air or j’acuum

cleaner. Use alcohol applied with a cleaning brush to

remove accumulation of din or grease from connector

contacts and component terminals.

Clean the exterior of the instmmenl and the front
panel with a mild detergent miscd with waler. applying
the solution with a sof1. lint-free cloth.

5-8. Repair and Replacement

Repair and rcplaccment of clcctrical and mechanical
parts must bc accomplished with great cam and caution

5-3

Printed circuit boards can become warped. cracked or
burnt from excessive heat or mechanical stress. The
following repair techniques are suggested to avoid in­advertent destruction or degradation of parts and assem­blies.

been subjected to conditions outside these ranges. allow
at least one additional hour for the instrument to stabi­lize before beginning the adjustment procedure.

5-9-2. Warm-Up Period

Use ordinary 60/40 solder and 3.5 to 40 watt pencil
type soldering iron on the circuit board. The tip of the
iron should be clean and properly tinned for best heat
transfer to the solder joint. A higher wattage soldering
iron may separate the circuit from the base material.
Keep the soldering iron in contact with the PC board for
a minimum time to avoid damage to the components or
printed conductors.

To desolder components use a commercial ” solder
sipper “. or better. solder removing SOLDER - WICK.
size 3. Always replace a componeut with its exact du­plicate as specified in the parts list.

5-9. Performance Checks

The following performance checks verify proper opera­tion of the instrument. and should normally be used :

a. As part of incoming inspection of instrument specifi­cations;

b.

As part of troubleshooting procedure:
c. After any repair or adjustment. before returning in­strument to regular service.

5-9-l. Environmental Conditions

Tests should be performed under laboratory conditions

having an ambient temperature of 25 f5 “C and a rela-

tive humidity of less than 80%. If the instrument has

Most equipment is subject to at Icast a small amount of
drift when it is first turned on. To ensure accuracy. turn
on the power to the Model 776 and allow it to warm-up
for at least 30 minutes before beginning the perform­ance tests procedure.

5-9-3. Recommended Test Equipment

Recommended test equipment for troubleshooting. cali­bration and performance checking is listed in table 5-Z.
Test instruments other than those listed may be used
only if their specifications equal or exceed the required
minimal characteristics.

5-10. Performance Checks Procedure

NOTE

The Models 776 and 77612.46 have
a default gate time of I second. The
Model 776/2.4G/R

time of 10Oms. The resolution of
counter readings in the following
procedures are for a 1 second gate

time. Readings on the Model

776/2,4G/R will have one less digit.

5-10-I. Channels A and 6 Sensitivity Check

Equipment: Synthesized signal generator
Procedure:

has

a default gate

Instrument

DMM
Pulse/Function Generator

Recommended
Model

Keithley 175A
HP 8116A

Minimum Use (*)

Specifications

.I V- 100 VDC. AC rms. 0.05% P.A.T

4 s - 20 ns

Synthesized
Signal Generator
Oscilloscope
DCV Calibrator

10 MHz Standard

HP 8663A
Tektronix 2465
Fluke

Oscillatec

100 KHz - 2.560 MHz

300 MHz band width T

I v - 100 v. 0.01% A

10 MHz fl0 E-12
50 Q feedthmugh
Termination

Tek 01 I-0049-01

50 n. 2

(*) P= Performance Test. A= Adjustments, T= Tmublesbooting

Table S-2. Required Test Equipment

5-4

w. 1%

P
P.A

P.A
P.A

1.

2.

3.

4.

5.

6.

7.

8.

9.

1.

2.

3.

1.

2.

Maintenance and Performance Tests

Figure 5-3. Channels A and B Sensitivity Test Set-up.

REAR PANEL CONNECTIONS

REF

SIGNAL GENERATOR

IN

RF

OUT

Connect the test equipment as described in Figure 5-3.
Press Model 776 push-buttons in the following

sequence [2nd] , [DCL] and then [50 Ω ] .

Set Synthesizer frequency and amplitude as given in
the following table and verify a stable counter readings as
follows:

SYNTH
FREQ

1 MHz

80 MHz
100 MHz
150 MHz
225 MHz

SIGNAL
LEVEL

50 mV
50 mV
50 mV
50 mV
50 mV

REQUIRED
READING

1.000000000 E+6

80.0000000 E+6

100.0000000 E+6

150.000000 E+6

225.000000 E+6

ALLOWED
ERROR

±2 MHz
±0.2 Hz
±0.2 Hz
±2 Hz
±2 Hz

Change synthesizer frequency setting to 10 MHz and

signal level setting to 50 mV rms.

Press [LPF] push-button and observe that the counter

does not process any more readings.

Again press [LPF] and then [x10] push-button and

observe that the Model 776 still does not process readings.

Change synthesizer amplitude level setting to 250 mV

rms.

Verify that counter reading is 10 MHz ±20 MHz.

Modify the connections in Figure 5-5 above so that
the synthesizer will now be connected to Channel B.
Select [FREQ B] .

10. Repeat the procedure above to verify Channel B sen-

sitivity.

UUT
MODEL 776
COUNTER/TIMER

C

10MHz

OUT

B

A

5-10-2. Channel C Sensitivity Check

Equipment: Synthesized signal generator
Procedure:

Connect the test equipment as described in Figure 5-4.
Press Model 776 push-buttons in the following

sequence: [2nd] , [DCL] and then [FREQ C] .

Set Synthesizer frequency and amplitude as given in
the following table and verify a stable counter readings as
follows:

SYNTH
FREQ

50 MHz
100 MHz
500 MHz

1000 MHz
2000 MHz
2400 MHz

SIGNAL
LEVEL

15 mV
15 mV
15 mV
15 mV
15 mV
15 mV

COUNTER
READING

50.0000000 E+6

100.0000000 E+6

500.000000 E+6

1.000000000 E+9

2.00000000 E+9

2.40000000 E+9

ALLOWED
ERROR

±1 LSD
±2 LSD
±1 LSD
±2 LSD
±1 LSD
±1 LSD

5-10-3. Period A, Period A Averaged

Operation Check

Equipment: Synthesized signal generator
Procedure:

Connect the test equipment as described in Figure 5-5.
Press Model 776 push-buttons in the following

sequence: [2nd] , [DCL] , [PER A] and then [50 Ω ] .

5-5

Maintenance and Pwformance Tests

Fieure S-4.

Channel C Sensitivitv

SIGNAL GENERATOR SIGNAL GENERATOR

> >

REP REP

IN IN

0% 0%

0 0

3. Set Synthesizer frequency to 1 MHz and amplitude
level to 50 mV runs.

4. Verify a stable counter readings as follows:

1.000 E-6 kl LSD

5. Press [2nd] and then [AVG] push-buttons.

6. Set Synthesizer frequency to 125 MHz and amplitude

level to 50 mv rms.

7. Verify a stable counter readings as follows:

8.00000000 E-9 52 LSD

REAR PANEL -CONNECTIONS REAR PANEL -CONNECTIONS

UUT UUT
MODEL 776 MODEL 776

I I

COUNTER/TIMER COUNTER/TIMER OUT OUT

IOMHZ IOMHZ

5-104. Ratio A/B Operation Check

Equipment: Synthesized signal generator
Procedure:

1. Connect the test equipment as described in Figure
5-6.

2. Press Model 776 push-buttons in the following se-

quence: [2nd]. [DCL]. [FRQIBI. [AC B]. and then

[Son A&B].

3. Set Synthesizer frequency to 22.i MHz and amplitude
level to 50 mV rms.

SIGNAL OENERATOR

Figure S-S. Perimi.~~

5-6

REF

IN COUNTER I TlMER OUT

and Period..1 Averaged Test &r-up.

REAR PANEL MXlNECTlONS

“UT
MODEL 776

,-

lOM”I

REAR PANEL

REF CONNECTION

OUT

c

SIGNAL GENERATOR

U”T
UODEL 776
COUNTER I TIMER

4. Verify a stable counter readings as follows: 3. Set Synthesizer frequency to 2000 MHz and ampli­tude level to 50 mV rms.

22.5000000

kl LSD

4. Verify a stable counter readings as follows:

5-105. Ratio C/B Operation Check

Equipment: Synthesized signal generator
Procedure:

1. Connect the test equipment as described in Figure

5-7.

2.

Press Model 776 push-buttons in the following se-

quence:

FrEQ

[Znd]. [DCL]. [2nd] [FRQ SEL].

C, [FRQIB]. [AC BI.

REAR PANEL

REP

CONNECTtON

OUT

c

and then [SOD

SIGNAL GENERATOR

and select

B].

ET

200.0000

+l LSD

5-108. Pulse A, T.I A to B, Pulse A AVG

and T.I. AVG Operation Check

Equipment: Pulse/Function generator
Procedure:

1. Connect the test equipment as described in Figure
5-8. It is essential that both cables to channels A and B

arc exactly equal in length.

“UT
WJOEL T76
COUNTER I TIMER

r 1

Figure 5-7.

Rntio C/B Test Set-up.

5-7

Maintenance and Performance Tests

Firmre 5-8.

PPG.

,

Pulse A. T.I.4 to B nnd.-lvemeed Test Set-uo.

,

EfF300

OUT

0 0 0

2. Press Model 776 push-buttons in the following se­quence: [2nd]. [DCL]. [PLS A] and then [5On A&B].

3. Set Pulse/function generator parameters as follows:
Output Wave form - Normal Pulse

Pulse Frequency - 18.2 KHz
Pulse Width - 20 ps
Pulse Amplitude - +2 Vp-p

4. Verify a stabkcounter readings as follows:

20.000 E-6 f.2 E-6

i

,

MODEL 776
COUNTER/TIMER

20.00000 E-6 i.2 E-6

7. Press [2nd] and then [AVG] to delete AVG function.

8. Select IT.1 A to B] and bB{ functions by pressing
the appropriate push-buttons.

9. Verify a stable counter readings as follows:

20.000 E-6 k.2 E-6

10. Press [2nd] and then

[AVGj

lo select T.I. A to B

AVG.

11. Verify a stable counter readings as follows:

5. Press [2nd] and then [AVG] to select PULSE A AVG.

20.00000 E-6 k.2 E-6

6. Verify a stable counter readings as follows:

“UT
MODEL 776

PPG.

f! ) , 1

Figure 5-9.

Phase .4 to B Test Set-up

COUNTERlTlMER

5-8

5-10-7. Phase A to B Operation Check

Equipment: Pulse/Function generator
Procedure:

1. Connect the test equipment as described in Figure 5-9. It is
essential that both cables to channels A and B are exactly
equal in length.

2. Press Model 176 push-buttons in the following sequence:
[2nd], [DCL], [Phase A-B], [ XA] and then [SOQ A&B].

3. Set Pulse/function generator parameters as follows:

Output Wave form-Normal Pulse
Pulse Frequency - 18.2 kHz
Pulse Width - 27.5 ps
Pulse Amplitude -S? Vp-p

4. Verify a stable counter readings as follows:

180.00 zk2.00

5-10-8. Totalize B Operation Check

Equipment: Pulse/Function generator
Procedure:

1. Connect the test equipment as described in Figure 5-10.

2. Press Model
[Znd], [DCL], [TOT B], [SOQ] and then [CLR].

3. Set Pulse/function generator parameten as follows:
Output Wave form _ Pulse

Pulse Frequency - 40 MHz
Pulse Width - IO ns

776

push-buttons in the following sequence:

Pulse Amplitude - +2 Vp-p

Trigger Mode - External Burst

Burst - 1999

Trigger Slope - Positive

4. Press the pulse/function generator MANUAL triefer puah­button. Verify a counter readings as follows:

1999

5. Again press the pulse generator MANUAL trigger push­button. Verify a counter readings as follows:

3998

5-10-g. Auto Trigger Level A and B Operation
Check

Equipment: Pulse/Function generator
Procedure:

1. Connect the test equipment as described in Figure 5-l I.

2. Press Model
[2nd], [DCL], [SOQ A], [2nd], [AUTO TRIG] and then [TL

Al.

3. Set Pulse/function generator parameters as follows:
Output Wave form -Normal Sinewave

Frequency - 50 kHz
Duty Cycle - 50%
Amplitude - 1 Vp-p
Offset - 4v

4. Verify that trigger level A reading is as follows:

776

push-buttons in the following sequence:

PPG.

Figure S-10.

Totolize B Test Ser-up.

OUT

“VT
MODEL 776

\

J

COUNTER I TIMER

s-9

Figure S-1 1. iluto Trigger A

PPG.

and B 7’esr Ser-np.

“UT

MODEL ,76

,

c

COUNTER/TIMER

4.00 v ti.20 v

1. Connect the test equipment as described in Figure
s-12.

5. Modify the connections in Figure 5-11 above so that
the pulse generator will now be connected to Channel
B.

6. Press Model

776

push-buttons in the following se-

2. Press Model

quence: [2nd]. IDCL]. [PER A]. ISOf A].IZndl

[DELAY]. [2nd]. and then [AUTO TRIG].

3. Set Pulse generator parameters as follows:

776

push-buttons in the followitlg se-

quence: [Znd]. [DCL]. [FREQ B]. [SOa B], (Znd].
[AUTO TRIG] and then [TL B].

7. Repeat the procedure above to verify Channel B auto
trigger level operation.

Output Wave form - Normal Pulse
Pulse Frequcnc) - SO KHz
Hi& Lewl - +2.0 V
Loi, Lez\%l - -2.0 v

5-10-10. Delav ODeration Check

Equipment: Pulse/Function generator

Procedure: approximately I s

4. Verify a counter reading as follows:

“UT
MODEL 776

PPG.

Maintennnce and Pe~fhmm km

REAR PANE‘ CONNECTIONS

UUT

EXT. GATE

INPUT COUNTEA/TlMER

c

MODEL 776

IOMHc

OUT

5-10-11. User Gate Operation Check

Equipment: Pulse/Function geuerator
Procedure:

1. Connect the test equipment as described in Figure
5-13.

2. Press Model 716 push-buttons in the followiug se­quence: [2nd]. [DCL]. [SO0 A] and then [AC A].

3. Select the USER GATE function on the counter.
(Refer to section 3 paragraph 3-17).

4. Set Pulse/function generator frequency to 667 mHz.
and pulse width to I s.

5. Verify a stable counter reading as follow:

10.00000000 E+6 zk2

TIME BASE STANDARD

5-10-12. Time Base Accuracy Check

Equipment: IO MHz standard
Procedure:

1. Connect the test equipment as described in Figure
5-1-I

2. Press Model 776 push-buttons in the following se­quence: ]2nd]. ]DCL]. ]SOn]. ]2nd] and then [AUTO

TRIG].

3. Verify a stable counter reading as follows:

10.00000000 E+6 f5OOO LSDs: or

10.00000000 E+6 ~ItlOO LSDs with option 2.4G installed:

ii!

i&EL 776

Cl

3UNTERITIMER

hfaintenance nnd Pet@wmnce Tests

NOTES

5-12

6

Theory of Operation

6-l. introduction

This section contains an overall functional description
of the Model 776 as well as detailed circuit analysis of
the various sections of the instrument. Information per­taining to the standard IEEE interface and the various
options are also included.

Information is arranged to provide a description of
individual functional circuit blocks. As an aid to under­standing. the descriptions are keyed to accompanying

block diagrams. and simplified schematics. Detailed

schematics and component layout drawings are located

at the end of this instruction manual.

6-2. Overall hnctional Description

Model 776 is a IO digit counter with 16 different meas-

urement functions as standard. and I additional meas-

urement function as an option. The counter utilizes a
modem technique. which combines both reciprocal. and
comentional measurement techniques. hence. increas-

ing resolution in low frequency measurements. as well
as. high frequency measurements: compared to other
available counters which utilize the more conventional­fixed-gate-time technique. As an example. a conven­tional counter measuring I KHz with a gate time of I

second will display a resolution of 1 Hz. where Model

776 with the same gate time will always display a

minimum of nine digits of resolution.

The heart of the instrument contains two counting
registers: Nl and N2. two synchronizers. selectors. and
gates. Figures S-I and 5-2 demonstrate the intcr-connec-

tion of these four elements. The Model 776. while per­forming frequency measurenients. will automatically
determine which one of these configurations are to be
used. The criteria for this decision is built into the

software. However. under certain conditions the counter
can only operate using the reciprocal technique (e.g.
Frequency C. hold. and single shot frequency measure-

ments).

During frequency measurement. using the reciprocal
measurement technique (Figure S-l ). Selector I routes
the input signal (F) to clock I (CLK I ). Selector 2 routes
the reference clock signal to clock 2 (CLK 2). The gate
time (GT) is generated by the CPU. and is synchronized
to the unknown input signal (CLK I) in such a way that
the synchronized gate time I (SGT I) now has a period
with an exact integer multiple of pulses from the un-

known input signal. Counter Nl then totalizes the nutn­ber of input pulses during the SGT I. Synchronizer #2
generates the synchronized gate time 2 (SGT 2) from

SGT 1. SGT 2 now has a period with an exact integer
multiple of pulses from the reference clock signal.

Counter N2 totafizcs the number of rcfercncc clock
pulses (CLK 2). The CPU then computes the result to
be displayed. using the follou,ing formula:

F=N1

N2 s T ~whcre: T = the period of the

reference clock

While performing frequency measurements above

100 MHz. the inler-connection configuration is auto­matically changed to USC the conventional mode of op­eration. as shown in Figure S-2.

6-l

Theory gf Operation

Figure 6-l.

Reciprocal Frequency~/easurement.

In this case, selector 2 routes the input signal (F) to
clock 2 (CLK 2). Selector 1 routes the reference clock
signal to clock 1 (CLK 1). The gate time (GT) which is
generated by the CPU is synchronized to clock 1 (CLK

1) in such a way that the synchronized gate time #l

(SGT 1) now has a period with an enact integer multiole

- .

of the reference clock pulses. Counter N1 then total&s
the number of the reference clock pulses during SGT 1,
Synchronizer#Z generates the synchronized gate time 2

(SGT 2) from SGT 1. SGT 2 now has a period with an
exact integer multiple of pulses from the input signal
(F). Counter N2 totalizes the number of input signal
pulses (CLK 2). The CPU then compotes the result to
be displayed, using the following formula:

. ._

F =x.-

Nl x T

where; T = the period of the refer­ence clock (CLK)

Figure

6-2

6-2. Conventional Frequency A~easurelncnt.

1

I I--

I
I

-I-

1

Theory of Operation

A simplified block diagram of the complete Model 776
is given in Figure 6-3. The input signal is applied
through the input amplifiers to switching circuits which
in turn routes the signals to the correct counting circuits.
If channel C is installed, a signal from the Channel C
input terminal will pass through the channel C input

amplifier to the internal selectors. The CPU. working

under software control, then converts the signals into a
form suitable for displaying on the front panel or for the
IEEE bus.

6-3. Analog

Circuitry

The following paragraphs contain a description of the
input

circuits,

measurement logic circuits, frequency
multiplier and of the power supply. These circuits may
be found on schematic diagrams located at the end of
this manual.

6-3-l. Input Circuits A and B

NOTE

Channels A and B are identical in
terms of components and operation.
Therefore. the following description.
which reviews only Channel A cir­cuits applies to channel B as well.
Note that letter designations for corn­ponents in Channel A are different
for similar components in Channel
B.

The signal which is applied to the Channel A input

terminal is preconditioned in front of the amplifier cir­cuit by means of relays and electronic components as

follows:

Coupling:

capacitor Cl. When instrument is DC coupled, Kl con-

tacts are closed. When instrument is AC coupled. Kl

contacts are open and Cl blocks the DC components of
the input signal.

Attenuation:

resistor network R3 and R39, and capacitor network C3

and C6. When K2 shorts between contacts 1 and 7. R3
and C6 are shorted and there is no attenuation. Actuat-

ing K2 shorts between contacts 7 and 14 thereby intro­duces a x-10 voltage attenuation.

Filtering:

K4. Contacts on K4 are normally closed; shoning R6.

When the relay contacts open, the impedance of R16,

and the capacitance of Q2 act as a low pass filter.

Coupling is controlled by a relay Kl, and

Attenuation is controlled by relay K3,

The low pass filter is controlled by relay

Termination:

Termination is controlled by relay K2.

Relay is normally open, leaving a 1 Ma impedance
(R4+R5) in front of the input amplifier. When the relay
contacts are closed, the input impedance is shunted by

RI and R2 (5051).

Input Protection:

Front panel input conditioning

arc capable of handling signals within the specified

dynamic

range

of the Model 776. Protection of the input

circuit from over-voltage signals (up to the specified

limits) are done by R4, clipping diodes within UlO, C8,

R7. CR 2 and Q2.

Amplifier:

The amplifier comprises aband split/dif­ferential amplifier. This section consists of a high fre­quency amplifier - Q2, and low frequency differential
amplifier - U 10 and QS. The two bands are summed at
the junction of R12 and RlO, and then buffered by 43.
The diode network - CR5 to CR8 limit the amplitude of
the signal which is then applied to the comparator Ul2a.
Ul2a operates as a Schmidt trigger amplifier which
translates, for the following stages, the various input

wave forms to an appropriate ECL logic levels.

Trigger Level Control:

The trigger level control
circuit generates a DC voltage which is directly propor­tional to the required input threshold point. This voltage

is then applied through R22 to the negative input of the
differential amplifier which was previously discussed.
U7 and U6 are a serial to parallel converters which
control the D to A converter - US, U9a, U9b, and their
associated components. The output of U9b generates a
dc voltage in the range of -5 V to +5 V. This voltage is
then applied. in parallel. to the rear panel TRIGGER
LEVEL A. and through the voltage dividerR2 I and R35
to the negative input of the differential amplifier.

6-3-2. Input Circuit C

The signal which is applied to the Channel C input
terminal is AC coupled through Cl to a 6 dB attenuator
R18 through R22. and through a limiting diode network
CR 1 through CR6. to the input of the first stage ampli-

ficr U 1. The amplifier section comprises three stage
amplifiers U 1 through U3 and their associated compo-

nents. Limiting diodes, CRS through CR13, prevent
saturation of the following stages. The signal from the
U3 is routed to a divide by 128 circuit - U4. The output
from this divider is ac coupled and dc leveled by R16
and R17. and then routed through Jl to the main board
assembly.

U4 is a self oscillating circuit, that is, if no proper
signal is available at its input, the output will
at an uncontrollable frequency. To prevent this oscilla-

oscillate

6-5

tion from reaching the counting circuit, a special com-

parator circuit is provided. This comparator detects the

magnitude of the signal at the input to the divider. Only
when the signal is within the specified limits, the output
of the divider will be gated to the rest of the circuit.

The signal at the input to U4 is dctccted by CR14.
C16, and C19. The ac signal is rectified and applied to
a comparator circuit - U5 and its associated compo­nents. The comparator then behaves just like a gate.
With an adequate signal this gate will release the output
of U4 to the subsequent circuits.

6-3-3. IQ MHz Standard Reference

Oscillator

The reference oscillator circuit contains an hybrid oscil­lator U57, buffers U56, and voltage regulator U55.
C124, C125, and CL.26 adjust the oscillator frequency
to a known reference. Cl24 is a coarse adjust, and C126
is a fine adjustment. LKIa/b is used for selecting be-

tween an internal reference, which is generated by U51,
and external reference frequency, which may be applied
to a rear panel BNC connector. CR35, CR36, C120. and
R192 protects the rear panel input against accidental
overloads. U56d is configured as a Schmidt trigger cir­cuit which converts the external amplitude level to TTL
level.

6-3-4. Reference Oscillator circuit, and

TCXO (option 2.4G).

The rcfcrence oscillator circuit generates a 500 MHz

signal for the Measurement Logic Section. The accuracy

of this signal is very high and is fed from a standard 10

MHz reference oscillator as described in paragraph 6-3-

3. The repetition rate of 500 cycles in one second is
generated by a voltage controlled oscillator (VCO) cir­cuit. The VCO is placed is a phase locked loop, and is
lock to the accuracy of the internal reference oscillator.
The accuracy of the overall circuit may be improved by

adding the TCXO. The TCXO Improves temperature

stability. as well as, long term stability of the entire
instrument. Figure 6-4 is a simplified block diagram of

the reference oscillator circuit.

The 500 MHz oscillator include 43, C23 through
C25, L2. varicap diode CR25, and their associated com­ponents. The 500 MHz output is buffered by U9, and
then simultaneously applied to J2 and to a divide by four
circuit - U3. 125 MHz from U3 isfurtherdividedby 100

by U4; the output of 1.25 MHz is then applied to the

phase comparator - U2. The output of the phase compa­rator is filtered, and buffered by U6, and its associated

components; its dc equivalent drives the varicap diode
which in turn controls the accuracy of the VCO oscilla­tions. The internal 10 MHz frequency reference is di­vidcd by 5 by U5. The output from U5 is applied as the
phase reference to the phase comparator.

6-6

Theory of Operation

Figure

6-5. Frequency A - Reciprocal, PeriodA Averaged, and Frequency A Conventional Signal Flow Diagram.

6-7

Theory of Operation

1

Figure 6-6.

6-8

Frequency Ratio A/B Signal l~‘lowDiagran~.

Theory

of

Operation

Figure

6-l. Period A, and Time Interval A to B Signal Flow Diagram,

6-9

Themy of Operation

Pigure 6-8.

6-10

L-J-

Pulse A Averaged and Time Interval A to B Averaged Signal Flow Diagram

r

.:ca‘Txa-

I==

Theory

of

Operation

Figure

6-9. Totalize B Infinite Signal Flow Diagram.

6-11

Theory of Operation

Figure 6-10.

6-12

Totalire B By A, and Totalize B By AA Signal Flow Diagram,

Theory of Operation

The reference oscillator also contains a phase noise
generator. During certain measurement functions, this
generator injects phase noise to the reference oscillator.

The noise generator is comprised of CR3, bias resistor
R9, and operational amplifier - U7. The noise generator

is switched in and out by an analog switch - U8 and is

controlled by 42 and its associated components.

6-3-5. Measurement Logic Section

The measurement logic section is a block which con­trolsvarious switching, routes the internal signals to the
correct ports. It also controls the sequence of the gate
and resets and synchronizes the main registers Nl and
N2 for the CPU. Figures 5-4 to 5-9 show the routes for
the input signal and the reference signal in every meas­urement function. The following is a brief explanation
of the various segments in the measurement logic sec­tion.

Control: The control circuit consists of U15, U14,
and U13. Information from the CPU is sent in a serial
form to the control ICs which in term convert the serial
information to a parallel format. The parallel outputs of
these ICs are being used to control the signal selectors,
and the signal routing to the various sections within the
measuring logic section. Qll through 413 convert the

TTL logic levels from the CPU to an appropriate voltage

levels for U15 (0 V to -5.2 V).

Signal Selector: The signal selector circuit com-

prises U19, U20, U21, U25, and U28. The function of
the signal selector is to route one of Channel A input.

Channel B input, Channel C input. or the reference

clock to the appropriate processing sections.

Time Interval Section:

circuit consists of ti dual D flip-plop U 17a/b. and gates
U18a, b and c, and Ul9b. U17a receives the start signal.
and U17b receives a stop signal. Following a reset
signal at the reset input of U17a/b, U18c simultaneously
produces a single positive pulse (TI), and its comple­ment with a duration which is equal to the time interval
between the start, and the stop signals, regardless if the
start and stop signals are repetitive. While performing
time averaged measurements, these pulses will repeat as
long as the gate stays open.

The time interval section

approximate width of the original gate signal from the

CPU. but with a new adjusted width which is equal to

an integer number of periods of the signal being meas-

ured. This pulse is used as the #I synchronized (SGT 1)
gating signal throughout the instrument. In conven­tional frequency measurements, (refer to the above de­scription), the gate time is synchronized to the reference
clock 1 (1.25 MHz). SGT 1 opens the gate U26d for the
appropriate signal to be later divided, and counted by
Nl dividing chain.

Synchronizer #2:

The

synchronizer

#2 consists of a
D flip flop U29b, gate U28d, and their associated com­ponents. During reciprocal frequency measurement,
SGT 1 signal is applied to the D input of U29b. At the
same time, the reference clock 2 (500 MHz) is applied
to the CLK input on the same IC. the output of U29b

generates a pulse SGT 2 with an approximate width of

SGT 1, but with a new adjusted width which is equal to

an integer number of periods of the reference clock 2.
In conventional frequency measurements, the gate time
is synchronized to the input signal. SGT 2 opens the gate
U28d for the appropriate signal to be later divided and
counted by N2 dividing chain.

Signal Identifier:

The signal identifier comprises
U22a. U31a, and their associated components. A signal
when present at the appropriate input terminal, is ap­plied to the CLK input of U22a, converted to a TTL
level signal with U3 la, and then fed to a CPU port 1.1.
This port is used to flag the presence of a signal at the
input terminals. This signal is also used as the arming
signal of the counter.

Gate Identifier:

The gate identifier informs the CPU on
the state of the synchronized gate time # 1. The gate identifier
circuit also serves as a time stretcher of gate signals having

very small periods. The gate identifier consists of U26a,

U26c. U31d, R158, and C86.

Nl Counter Chain: The Nl counter chain comprises
U30b, U31a. U27a, U23a, U46a, U44, and their associated
components. U3Ob, U27a, U23a, and U46a are configured
as 7 bit binary up counter

with

its output connected to U44.
U44 is a 32 bit counter with its outputs connected to the data
bus. U31c converts the ECL logic level from U30b to Tn.

Synchronizer #l:

The synchronizer #l consists of a
D flip flop U22b. gate U26b/d, and their associated
components. During reciprocal frequency measure­ment, a gate signal is applied from the CPU to the D
input of U22d. and the measured signal is coupled to the
CLK input on the same IC. After a reset cycle, and
assuming that a signal is present at the appropriate input
terminal, the output of U22b generates a pulse with an

N2 Counter Chain:

The N2 counter chain comprises
U29a, U3Oa, U3lb. U27b, U23b, U46b. U45, and their
associated components. U29a, U3Oa, U27b, U23b, and
U46b are contigured as 8 bit binary up counter with its
output connected to U45. U45 is a 32 bit counter with its
outputs connected to the data bus. Ql5 and U31b convert
the ECL logic level from U29a, and U30a respectively to
T-l-L.

6-13

Theory of Operation

6-3-6.

For the following discussions, refer to the power supply
schematic at the end of the manual. The power supply is
made up of a line fuse, power on-off switch, line voltage
selection switch, power transformer, two bridge rectifiers.
two monolithic regulators, and hvo discrete regulators
which is formed by U52, 430, 431, Q32, Q39, and their
associated

Fuse F1 is the LINE FUSE which is accessible on the rear
panel. S2 is the LINE VOLTAGE SELECT switch, which

is accessible on the rear panel, to select 115 V or 230 V
operation and Sl is the power on-off switch. CR25 is used
as a full-wave rectifier to provide a sufficient DC voltage
for the +I2 V, and -12 V regulators U50, and U51 respec­tivdy.

V supply. This reference is then compared to the regulated
+5 V U52b then controls through Q30 the current through
the series pass transistor - 43 1. The +5 V supply then acts
as the reference for the -5.2 V regulated supply. The opera­tion of U52a is similar to the operation of US2b, except,
US2a operates as an inverting amplifier. CR 29, and CR30
protect the +5 Vand the -5.2 V respectively against acciden­tal over-voltage.

Power Supply

components.

U52b receives a reference voltage of +5 V from the +I 2

6-4. Digital Circuitry

Model 776 operation is supervised by the internal CPU.
Through the CPU, the counter measurement process, the

front panel switching, display, and IEEE operation are
all performed under software control. This section
briefly describes the operation of the various sections
of the CPU, and its associated digital circuitry. A sim­plified block diagram is included for user reference; for
more complete circuit details refer to digital schematics
at the end of this manual.

6-4-l. CPU Block Diagram

A block diagram of the Model 776 CPU is shown in
Figure 6-3. Circuit operation centers around the CPU
unit - U39. The 803 I is an S-bit CPU capable of directly
addressing up to 64K bytes of program memory (ROM),
and up to another 64K bytes of data memory (RAM).
The CPU works with a 16 MHz clock which is divided
internally to provide a bus operation of about 1.6 MHz.

Interfacing between the CPU, and the IEEE bus is
performed by dedicated IEEE-488 bus interface IC ­U36. This IC performs many bus functions automat­ically to minimize CPU overhead. Buffering between
the 8291 IC and the IEEE bus lines is done with bus
drivers U21 and U22.

Interfacing between the CPU to the keyboard and the
display is performed by the Keyboard/Display interface
IC - U36.

64-2. Memory Mapping

The 8031 CPU is capable of directly addressing two
banks of 64k (65,536) bytes memory. One bank of mem­ory is the program memory, and the second memory
bank is the data memory. The selection of the banks is
done internally by the CPU. Although the CPU has this
large addressing capability, only a portion of the possi-

ble memory space is actually needed.

The Model 776 uses a total of 32K of program
memory stored in the 27256 EPROM U43, and a total
of IK of data memory is stored in UIO and. The 8031
CPU uses a memory-mapped I/O scheme, additional
memory location must be allocated for the various I/O
function. All the memory-mapped II0 functions are in

the data memory space.

6-4-3. Address Decoding

The CPU has a total of 16 address lines which are used
to locate a specific memory slot. The LOW address line
(A0 to A7) are multiplexed on the address/data bus, and
the ALE (address latch enable) signal is used to separate
the LOW address from the address/data bus witch is
done by U40 address latch. Since no memory or inter­face element can fully decode address locations, addi­tional address decoding must be used. U38 is l-of-8
decoder. The decoder is enabled when address lines Al5
is HIGH. Once the decoder is selected the decoding is
done by addressing lines All, A12 and A13.

6-4-4. Keyboard/Display Interface

The Keyboard/Display Interface IC US is used to con­trol the front panel display, and to find out which one of
the buttons was pushed.

Software for the CPU is contained in an EPROM
(Erasable Programmable Read-Only Memory). U42 is a
27128 EPROM containing 16K bytes of software. Tem-

porary storage is provided by U43, RAMS (Random

Access Memory) which can store up to 2048 bytes of
information.

6-14

6-4-5. IEEE interface

The Model 776 has a built in IEEE-488 interface that
allows the instrument to be controlled through the sys­tem controller. Commands may be given over the,bus,
and data may be requested from the instrument as well.

The IEEE interface is

made

up of U47, a 8291 GPIA

active low with approximately zero volts representing a

(General Purpose Interface Adapter), U48. and U49. logic enc. The two IEEE bus drivers, U48 and U49 are

which are interface bus drivers. On the CPU side of the

ncccssary to bring the drive capability of the interface

GPIA, data transmission is handled much like any other unto the normal IEEE maximum 15 devices.
bus transaction. The CPU accesses the GPIA through
the usual DO through D7 data lines. Address decoding
for the internal 14 registers (7 read and 7 write) is

provided by the CS, WR, RD, and AO, A 1, A2 terminals,

The output of the 8291 IC is a standard IEEE format;
the eight data lines (DIOl through DI08), the three
handshake lines (DAV, NDAC, NRFD), and the five

The GPIA simplifies CPU interfacing to the IEEE

bus because many control sequences take place auto-

matically. For example, when a write is done to the data
outnut reeister. the handshake seouence is automaticallv
performed at the proper time. iithout the GPIA chip,
complicated CPU routines would be required to accom­plish control sequence that are performed automatically.

management lines (ATN, REN, IFC, SRQ, EOI), are all

6-15

Theory of Operation

NOTES

6-16

Adjustments and

Troubleshooting

7-1. Introduction

This section contains information necessary to adjust
and troubleshoot the Model 776 and the 2.1G option.

WARNING

The procedures described in this sec­tion are for use only by qualified
service personnel. Do not perform
these procedures unless qualified to
do so. Many of the steps covered in
this section may expose the individ­ual to potentially lethal voltages that
could result in personal injury or
death if normal safety precautions
are not observed.

7-2. Adjustments

7-2-l. Environmental Conditions

Adjustments should be performed under laboratory con­ditions having an ambient temperature of25’15 “C. and
a relative humidity of less than 70%. If the instrument
has been subjected to conditions outside these ranges.
allow at least one additional hour for the instrument to

stabilize before beginning the adjustment procedure.

776. and allow it to warm-up for at least 30 minutes
before beginning the adjustment procedure.

7-23. Recommended Test Equipment

Recommended test equipment for calibration is listed in
Table 5-2. Test instruments other than those listed may

be used only if their specifications equal or exceed the

required cha~racteristics.

7-24. Adjustment Procedures

All adjustments are performed with the POWER switch
ON. The top cover should be removed to allow access
to test points, and adjustments. Between adjustments.
always leave top cover on the unit to keep intcmal
temperature.

WARNING

Take special care to prevent contact
with live circuits. or power line arca
which could cause electrical shock
resulting in serious injury. or death.
Use an isolated tool when making
adjustments. Use plastic or nylon
screwdriver when adjusting the time
base trimmer: other materials could
cause confusion in this adjustment.

7-2-2. Warm-Up Period

Most equipment is subject to at least a small amount of

drift when it is first turned on. To ensure long-term

calibration accuracy. turn on the power to the Model

Refer to Figure 7-1. throughout the following adjust-

ment procedures. for determining adjustment points.

Follon, the procedure in the sequence indicated because

some of the adjustments are intcrrelatcd. and dcpcndent
on the proceeding steps.

7-l

Adjuments and Troubleshooting

Figure 7-l.

Model 776Adjus1ment Poinrs Locntion,

Verify that Model 776 is functioning according to
the performance checks. Make sure that all results are
within. or close to. the range of the required specifica­lions. Othcrwisc refer to the troubleshooting procedures
given later in this section. Ccntcr all trimmers and if
necessary. remove selected components and clear the
holes to allow a selection of nc\v components.

Perform the following adjustment procedure. If an
adjustment can not be made to obtain a specific result.
refer to the troubleshooting procedures.

7-3. Adjustment Procedure
7-3-l. Power Supply Adjustment

Equipment: DMM
Procedure:

1. Set DMM to DCV measurements. Connect the DMM

between ground, and the +5 V test point.

2. AdjustR190foraDMMreadingof+5.000VilOmVdc.

7-34. Trigger Level A Offset Adjustment

Equipment: Function generator. oscilloscope
Procedure:

1. Set function generator controls as follows:
Wave form - Sine

Frequency - I KHz
Amplitude - 25 mVp-p
OffSCl - II v

Syllllllctry 50%

2. Press Model 776 push-buttons in the following sc­qucncc: [2ndj.

[DCL]

and then

[AC Al.

3. Connect the function generator output to tbc Channel
A input connector.

4. Set oscilloscope time base to 0. I msfdiv.

5. Connect the oscilloscope probe to U21 pin 9. Connect

the ground lead from the probe to ground.

6. Adjust R83 to obtain a square wave having a 50%

*l% duty cycle on the oscilloscope.

73-5. Trigger Level B Offset Adjustment

73-2. Trigger Level A Adjustment

Equipment: DMM. dc voltage calibrator
Procedure:

1. Set DMM to DCV measurements.

2. Set

[TL A]

to 0.00 V

3. Measure and record the voltage at Ul2 pin 8. Record this
voltage with a resolution of +tLOOl V.

4. Set

[TL A]

to 5.00 V

5. Set dc calibrator output setting to +5.000 V

6. Using a banana to BNC adapter. connect the calibrator
output to the Channel A input connector,

7. Re-connect the DMM probes to U 12 pin 8 and adjust RSO
to obtain the same voltage level as recorded in step 3.

73-3.. Trigger Level 6 Adjustment

Equipment: DMM. dc voltage calibrator
Procedure:

1. Set DMM to DCV measurements.

2. Set

ITL B]

3. Measure. and record thevoltage at U12 pin 9. Record this
voltage with a resolution of M.001 V

4. Set

[TL B]

5. Set dc calibrator output setting to +5.000 V

6. Using a banana to BNC adapter. connect the calibrator
output to the Channel B input connector.

7. Resonnect the DMM probes to U I2 pin 9. and adjust R81
to obtain the same voltage Icvol as recorded in step 3.

to 0.00 V

to

5.00 V

Equipment: Function generator. oscilloscope
Procedure:

1.

Set function generator controls as in paragraph 7-3-4.

2. Press Model 776 push-buttons in the

quence: [2nd].

[DCL]. [FRQ B]

and then

following se-

[AC Bj.

3. connect the function generator output to the Channel
B input connector.

4. Set oscilloscope time base to 0.1 ms/div.

5. Connect the oscilloscope probe to U24 pin I-I Con­nect,the ground lead from the probe to ground.

6. Adjust R84 to obtain a square wave haying a 50%

+l% duty cycle on the oscilloscope.

73-6. input A x10 High Frequency

Adjustment

Equipment: Function generator. oscilloscope
Procedure:

1. Set function generator controls as follows:

Wave form - Square wave

Frequency - IO KHz

Amplitude - 5 Vp-p

Offset - 0 V

Symmetry - 50%

2. Press Model 776 push-buttons in the following se-

quence: [2nd].

3. connect the function generator output to the Channel
A input connector.

[DCL]. [SO!2 A].

and then 1x10

A].

7-3

4. Connect the oscilloscope probe to the cathode of
CR6. Connect the ground lead from the probe to ground.

5. Set oscilloscope and adjust C3 to obtain the best
square wave response having minimum overshool. and
undershoot.

7-3-7. Input B x10 High Frequency

Adjustment

Equipment: Function generator. oscilloscope
Procedure:

1. Set function generator controls as in paragraph 7-3-5.

2. Press Model 776 push-bu(tons in the following se-

quence: [Znd]. [DCL], [FRQ B]. [5On B]. and then

[xl0 B].

3. Connect the function generator output to the Channel
B input connector.

4. Connect the oscilloscope probe to the cathode of
CR14. Connect the ground lead from the probe to

ground.

5. Set oscilloscope and adjust C28 to obtain the best

square wave response having minjmum overshoot. and
undershoot.

NOTE

The Models 776 and 77612.46 have
a default gate time of 1 second. The
Model 776/2.4G/R has a default gate
time of lOOtus. The resolution of
counter readings in the following
procedures are for a I second gate
time. Readings on the Model
776/2.4G/R will have one less digit.

7-3-8. Standard - 5 PPM Time Base

Adjustment

If range can not be reached. sclcct Cl 25 (in the range of
8 - IOpF) lo bring Cl24 within range.

5. Replace the top cover. and allow the Model 776 tO
operate with the coverson foranadditional periodof lj
minutes.

6. Using a plastic mawrial screwdriver. adjust Cl26
from the rear panel to give a display reading of:

10.00000000 E+6 flOOO LSD

If range can not be reached. repcat steps 4 through 6.

7-3-9. TCXO Time Base Adjustment

(option 2.4G)

Equipment: 10 MHz Standard
Procedure:

1. The following adjustment musl be performed in a
stable temperature environment of 2.5 “C +2 “C Remove
the top cover. refer to Figure S-1. and remove the adjusl­ment plug at the top of the oscillator bulk. Replace the
top cover. Power-up Model 776. and allow it to operate.

for at leasl half an hour. with its covers closed.

2. Press Model 776 push-buttons in the following se-

quence: [2nd]. ]DCL]. and then ISOn

3. Connect the IO MHz standard to the Model 776
Channel A.

4. Remove the top cover. and using a plastic-tip screw-

driver. ad.just the trimming resistor on top of the TCXO
board to give a reading of:

10.00000000 E+6 irIO LSD

5. Replace the ad,justment plug and the top cover. and

allow the Model 776 to operate with the covers on for
an additional period of 15 minutes.

6. Check if frequency is still in the range. as in step 4.
If reading shifted, repeat steps 4 through 6.

A].

Equipment: IO MHz Standard
Procedure:

1. The following adjustment must be performed in a
stable temperature environment of 25 “C +2 “C Remove

the top cover. and set Cl26 to about mid-range. Replace
the top cover. Power-up Model 776. and allow it to
operate. for at least an hour. with its covers closed.

2. Press Model 776 push-buttons in the following se-

quence: [2nd]. [DCL]. and then [SO.0

3. Connect the 10 MHz standard to the Model 776
Channel A.

4. Remove the top cover. and adjust CI2-l to give a
reading of:

10.00000000 E+6 f5000 LSD

7-4

A].

7-4. Troubleshooting

The troubleshooting instructions contained in this sec­tion are intended for qualified persomiel having a basic
understanding of analog. and digital circuitry The indi-

vidual should also be experienced at using @pica1 tc~(
equipment as well as ordinary troubleshooting proce-

dures. The information presented here has been written

to assist in isolating a defeclive circuit. or circuit sec­tion: isolation of the specified component is left to the

technician

74-l. Recommended Test Equipment

The success or failure in troubleshooting a complcs
piece of cquipmcnl. like the Model 776. dcpcnds noI

Table 7-l. Recommended Minimum Test Equipment For Troubleshooting

Adjusrmenrs and Troubleshooting

1”strume”t

DMM
Pulse/Function Generator
Signal Generator

Oscilloscope

Recommended
Model

Keithley 175A

HP 8116A 4 s - 20 ns. 15 Vp-p into 50 Q
HP 8663A 100 KHZ - 2560 MI-k
Tektronix 2465 300 MHz band width

50 ohm feed through

Termination

Tek 011-0049-01 50 R 2w. 1%

only on the skills of the technician, but also relies
heavily on accurate, reliable test equipment. Table 6-2
lists the recommended test equipment for a complete
troubleshooting and adjustment of the Model 776. How­ever. it is also possible to troubleshoot Model 776 with
the minimum equipment which is listed in Table 7-1.
Other equipment such as logic analyzer. and in-circuit
emulatoretc, could also be helpful in difficult situation.
71-2. Power-Up Self Diagnostics
An advanced feature of the Model 776 is its self diag­nosing capabilities. Upon power-up the Model 776 per­forms a set of tests which is described in paragraph 3-1.
If the Model 776 locks up due to ROM or RAM fail,

there is a little point in attempting to troubleshoot else­where unless the micro controller circuit is operating
properly.

Minimum
Specifications

.l V- 100 VDC. AC nns. .OS% basic accufac?~

7-5. Troubleshooting Procedure
7-5-l. Power Supply Checks

It is highly suggested that the first step in troubleshoot-

ing the Model 776. as well as any similar equipment,
would be
supply voltages within the instrument are not within the
required limits. troubleshooting the remaining circuits
can be vety difficult. Table 7-2 shows several checks
that can be made to the power supplies within the Model

776. In addition to the normal voltage checks. it is also
a good idea IO check the various supplies with a” oscil­loscope to make sure no noise or ringing is present.

In case of a “dead short” between one of the supplies

to the common ground. it would be best to disconnect

to

check the power supply. If the various

Step Item/Component

1

S2 Line Switch

2

Fl Line Fuse

3 Jl Line Power

4

+12 v Supply

5

u50 Input

6

-12 v Supply

7

u51 Input

8

+5 v Supply

9 Input to +5 v suppl)

10

Reference to +5 V
11 -5.2 V Supply
12 Input to -5.2 v
13

+5 v Supply to osc.
14 Input to +5 v us5

Table 7-2. Power Supply Checks

Required Condition Remark8

Set to 115 V or 230 V
Continuity

See paragraph 5-2

Remove fuse to check
Plugged into live receptacle;
power on
+12 v f5%
+I5 V minimum

Positive output of CR25

-12 v lt5%

-15 V minimum
+5 v *2%
Appros. +7 V
+5 v *5%

-5.2 V i2%
Appros. -7 V
+ 5 v f5%
112 v

Negative output of CR25

Cathode of CR29

Positive output of CR28

U52b pin 5 Supply

Anode of CR30

Negative output of CR28 Supply

U57 pin 8

U55 input/+ 12 V supply

7-5

Adiustments and Troubleshooting

In case of a “dead short” between one of the supplies
to the comtnon ground, it would be best to disconnect
the entire supply section from the remaining of the
circuitry, and then determine whether the problem is in
the power supply or in the remaining circuits. Model
776 is equipped with such quick-disconnect points.
which are located on the bottom side of the main PC
board. To access these points. it is necessary IO remove
the bottom cover. and then to remove the solder layer
from these points.

While troubleshooting the power supply section.
bear in mind that the +I2 V supply also provides the
reference voltage to the +5 V Therefore. it would be
impossible to troubleshoot the +5 V supply if the +I 2 V
supply is defective. Similarly. the +5 V supply is used
as a reference voltage to the -5.2 V supply.

74-2. Digital Circuitry and Display Checks

The most important section, to be verified after the
power supply checks, is the digital section with its
various clocks. Problems with the digital circuitry could
cause erratic operation or false display readings. Prob-

lems in the clock generator for the CPU and the digital

circuit may cause a complete malfunction of the entire
section. The CPU would not even start to generate the
control lines which makes it impossible to troubleshoot
the remaining of the circuitry. Check the various com­ponents, associated with the digital circuitry. clocks.
and the IEEE-488 interface. using the information in
Table 7-3.

7-53. Standard 5 PPM Reference

Oscillator Checks

The reference oscillator supplies a precise signal to the
500 MHz oscillator. This oscillator is integrated within
a phase locked loop. Therefore. the accuracy of this
oscillator determines the final accuracy of the 500 MHz
oscillator. Without this clock the instrument will oper­ate erratically. Verify that a 10 MHz TTL level signal is
present at U57 pin 5. U56 pin 6. 3. and 8. and at the
CLOCK output

position.

rear

panel connector. Check LKlaib

7-54. 500 MHz reference oscillator and

TCXO Checks

The 500 MHz oscillator circuit generates an ECL signal
for the counting circuit. This generator is a free running

voltage controlled oscillator. Its final accuracy is phase

locked to the IO MHz clock refcrcncc. Problems with
the 500 MHz oscillator will definitely cause false re­sults on the Model 776: in some cases. the counter may
display no result at all. Problems in the 500 MHz oscil­lator may bc identified using Table 7-1. When option 5 I
is installed. a TCXO reference replaces the standard

reference oscillator. The TCXO enhances the overall
accuracy of the insttumcnt. A malfunctioned TCXO
displays similar symptoms to an inoperative 500 MHz
oscillator. If a problem appears to be with the 500 MHz
oscillator, it is recommended that the TCXO outpul be
checked first.

7-5-5. Trigger Level Checks

The trigger level circuits control the threshold point
where the input circuit triggers. If a legal signal is
applied to the input connector. and the counter fails to
trigger. it is most likely that the fault is in one of the
trigger circuits. Problems within the trigger circuit may
be located using the checks given in Table 7-S.

74-6. Signal Conditioning And Input

Circuits Checks

Problems in these circuits could generate false results
on the Model 776. Tables 7-6 and Table 7-7 list the
checks to be made on the signal conditioning and the
input circuits respectively.

74-7. Measurement Logic Section Checks

The measuretncnt logic seclion circuitry is mainly used
as a digital traffic control to the analog signals within
the instrument. The function control circuit cheeks is

given in Table 7-8. Table 7-9 describes the remaining of
the measurement logic circuit. While performing cheeks
from Table 7-9. it is recommended to use a special high

frequency probe with very short grounding clip.

7-6

Table

7-3. Digital Circuitr.v and Display Checks

Step Tested Circuit

1

Required Condition

Turn on power Some tests here could

Remarks

fail due to digital problems.

2

Microprocessor clock

3

Microprocessor timer 0 to +4 V 7.8 KHz square w’ave

4

Keyboard/Display clock 0 to +4 V 2.0 MHz square wave

5

IEEE Interface clock

6

Beeper clock 0 to +4 V 3.9 KHz square wave Pin 1 on U41.

7

Reset Input Turn off instrument then back on

0 to +4 V 16 MHz square wave

0 to +I V 8.0 MHz square wave

Pie 18 on U39.
Pin 14 on U39.
Pin 3 on U36.
Pin 3 on U47.

Pin 9 on U39 stays low for

about .l s and then goes high.
8 ALE Line
9

PSEN Line 0 to +4 V 190 ns negative going pulses Pin 29 on U39.
10 RD WR Lines
11 Address/Data Bus

0 to +4 V 125 ns pulses
0 to +4 V 500 ns negative going pulses Pins 16 and 17 on U39.

0 to +4 V variable pulse train

Pin 30 on U39.

Pins 21 thou 28: Pins 32 thru 39:
Pins 3 thru 10 on U39 on U42.

Depress and hold the fi Level A during the nest six tests.

This will generate serial data on the RXD lines.
12 TTL Serial Data Input

0 to +5 V variable pulse train

Pin2ofUl:Pin2ofU3:
Pin 2 of U6: and. Pin 2 of U7.

13 ECL Serial Data Input

-5.2 to 0 V variable pulse train

Pin 2 of U15: Pin 2 of U14: and.
Pin 2 of u13.

I4 TTL Serial to Parallel

Converters Clocks

0 to +5 V bursts of pulse train

Pin 4 of U37: Pin 3 of Ul:
Pin 3 of U3: Pin 3 of U6: and.
Pin 3 of U7

15 ECL Serial to Parallel

-5.2 to 0 V bursts of pulse train

Pin3 ofUl5: Pin3 ofUl4:and.

Converters Clocks Pin 3 of U13

16 TTL Serial to Parallel

Converters Strobes

0 to +5 V bursts of pulse train

Pin IS of U37: Pin 1 of Ul:
Pin 1 of U3: Pin 1 of U6: and.
Pin 1 of U7

17 ECL Serial to Parallel

Converters Strobes

-5.2 to 0 V bursts of pulse train

Pin 1 of U15: Pin 1 of Ul4; and.
Pin 1 of U13

Depress. in turn. each one of the buttons on the front panel throughout the nest test.
This test will check all buttons on the front panel as well as the interrupt line.

18 Keyboard Interrupt Line 0 to +4 V variable negative going pulses Pin4ofU36
19 LEDs Sink Lines

0 to +4 V variable pulses

Pins 10 to 16 on U35: and.
Collector of 420

7-7

Adjustments ctnd Troubleshooting

Table 7-4.500

Step Tested Circuit Required Condition Remarks

1

2

hlHz Oscillaror and TC.\-0 Circuif Cluxks

Turn on power

TCXO IO MHz

0 to +4 V pulses

Phase Detector Signal

I 3

Input 0 to i-4 V 1.25 MHz pulses U2 pin 3.

4

Phase Detector Compare
Input 0 to +4 V 1.25 MHz pulses U2 pin 1. and U-l pin 2.

S

Low Pass Filter Out *l V around -0.5 V U6 pin 6.

Perform the following check with a I:10 probe. and a sampling osciIloscope

6

vco out 500 MHz pulses 1 Vp-p around -1.3 V 12

7

Noise Generator Approximately 200 mVp-p white noise U7 pin 6.

Table 7-5.

Trtnaer Level Circuit Checks

Step Tested Circuit Required Condition Remarks

1

2

D to A Reference +6.2 V +300 mV

Turn on power

Change front panel trigger level setting for Channels A and B to +O.OO V

3

Channel A Trigger Level +O.OO V &35 mV

4

Channel B Trigger Level +O.OO V t35 mV Pin 7 of U5

Ultl pi” 1. Ul pins 9. 10. and I I.

Pi” 15 of U4. and Pin 15 of US

Pin 7 of U9

Change front panel trigger level setting for Channels A and B to +5.00 V

5

Channel A Trigger Level +5.00 V +lOO mV Pin 7 of U9

6

Channel B Trigger Level +5,00 V +I00 mV

Table 7-6. .Si.wnl

Step Tested Circuit

Conditioning Checks

Required Condition

1 Turn power on

Input conditioning signals:

DC

AC
Filter On
Filter off

6 50 n
7 IMQ

8 Negative Slope
7 Positive Slope
9 Sl

10 xl0

+0.5 V dc
+5 V dc
+5 V
+O.S V dc
+0.5 V dc
+5 V dc
+0 V

-5.2 V dc
+5 V dc
+0.5 V dc

dc

dc

Pin 7 of U5

Remarks

The following lcsts are
performed on U2

Chamvel A

Pin 14
Pin 14
Pi” 15
Pin 15
Pin 12
Pin 12
U13 Pi” 11
U13 Pin 11
K3 Pin 6
K3 Pi” 6

Channel B
Pin 11

Pin 11
Pin 13

Pin I3
Pin IO
Pin 10

U13 Pi” I4

U13 Pin 14

K7 Pin 6
K7 Pi” 6

7-8

Table

I-1. Input Circuits Checks

Adjustments and Troub1eshootin.g

Step Tested Cirrnit

1

:, 2

Table

Chaonel A Input Amplifier 1 MHz ,150 Vp-p sine

3

Schmidt Trigger Operation A -1.7 V to -0.8 V 1 MHz square wave

4

Channel B Input Amplifier 1 MHz ,150 Vp-p sine

5

Schmidt

7-8. Function Control Circuit Checks

Trigger Operation B -1.7 V to -0.8 V 1 MHz square wave

Rcquircd Condition

Turn on power

Remarks

Apply 1 MHz .2 Vp-p sine

Press [2nd], [DCL] to Channel A input BNC

CR6 Cathode
Pin 1 on U12

Select FREQ B function Apply I MHz .2 Vp-p sine

Channel B input BNC
CR14 Cathode

Pin 16 on Ul2

to

Step

Tested

Circuit

Required Condition Remarks

1 Turn on power

Press

[2ndj. [DCL]. Apply 1

MHz 1 V p-p sine

10 Channel A input BNC.

2 Signal Selector #I -1.7 V to -0.7 V 1 MHz square wave

Pin 3 of LIZ.5

3 Synchronized Clock #l -1.7 V to -0.7 V 1 MHz bursts. Pin IS of U2G

Duration of burst is appros 1 s

The following are variable TTL/ECL level signals

with about 1 s burst duration - square waves.
Square wave period

4

Nl Divider Chain

2 1s

4 PS

8 PS

16 ps

32 ps

64 ps

U30b Pin 14 (ECL)
IJ31 Pin 12 (TTL)
U23 Pin 5 (TTL)
U4G Pin 11 (TTL)
U4G Pin 10 (TTL)

U46 Pin 9 (TTL)

128 ps U46 Pin S (TTL)

Signal Identifier

5

6

Gate Identifier TTL low level when gate is open. U31 Pin 13

TTL low level during measurement cycle.

U3 1 Pin 4

For the following check use a sampling oscilloscope with a 1: 10 probe

7 Synchronized Clock #2

-1.7 to -0.7 V 500 MHz bursts. Pin 15 of U28

Duration of burst is appros 1 s.
The following are variable signals with about 1 s

burst duration - square waves.

N2 Divider ‘Chain

8

9

Start/Stop Signal

10 Time Interval
11 Gate Identifier

7-10

Square wave period

ECL 4 ns
ECL 8 ns
ECL 16 ns
TTL 32 ns
TTL 64 ns
TTL 128 ns
TTL 256 ns
TTL Sl2 ns

Change panel setting to PER A,

-1.7 V to -0.7 V I KHz square wave

-1.7 V to -0.7 V 1 ms negative going
pulse for each cycle
TTL low level for 1 ms.
TTL high for about 300 ins after
gate closure

U29 Pin 3
U30 Pin 3
U27 Pin 14
U23 Pie 9
U46 Pin 3
U46 Pin 4
U46 Pin 5
U46 Pin 6

Apply 1 KHz I Vp-p square
wave to Channel A input BNC

U17 Pin 9
Ul8 Pin 15

U31 Pin 13

8

Parts List

8-1. General

This section contains information for ordering replace-

ment parts. the replacement parts are available from the
vendors listed or from Keithley Instruments. Mechani­cal parts are shown separately on Figure 8-l.

8-2. Ordering Information

When ordering replacement parts. always include the
following information:

a) Instrument Model number.
b) Instrument Serial number.
c) Keithley part number.
d) Part description.
e) Circuit designation (where applicable).

Keithley will do its best to improve the instrument and
make changes in style of components and replacement
parts. Replacement parts may differ in appearance from
those found in your instrument but are always equal or
superior in performance.

8-3. Parts Description

In the following Parts List Tables. unless otherwise
noted. resistors power rating is ll4W. resistance is

given in Q and capacitance is given in pF.

Some parts in the following pans lists are marked with
an asterisk (9 These parts belong to the standard time
base circuit. These parts will not be assembled when
option 2.4G is installed.

Matched or selected components may only be bought
from the factory. Selection guides for such components

are not given anywhere in this manual.

8-l

DWG PART
REF NUMBER

DESCRIPTION

DWG PART

REF NUMBER

DESCRIPTION

Cl

1521.04730
1500-01040

c2
c3

1550-01600

c5

1500-01040

C6

151 O-03ROO
1500-01040

c7

C6

151 o-06200

1500.01040

c9
Cl0

1500-01040

Cl1

1500-01040
1500-01030

Cl4
Cl5

1500-01040

CT6

1510-06200

Cl7 1500-01040

1500-01010

Cl6

1500-01010

Cl9

c20

1500-01040

c21

1500-01040
1560-01040

c22

C23

1540-01060

C24

1500-01040

C2S

1500471010

C26

1521.04730

C27

1500-01040

C28

1550-01 BOO
NOT USED

c29
c30

1500.01040

c31

151 O-03ROO
1500-01040

C32
c33 151 o-06200

1500-01040

c34
c35 1500-01040
C36 1500-01040

NOT USED

c37
C36 NOT USED

1500-01030

c39
c40 1500-01040

151 o-06200

c41
C42 1500-01040
c43 1500-01010
c44 1500-01010

1500-01040

c45
C46

1500.01040

c47

1540-01060
1560-01040

C48
c49

1500-01040

c50

1500-01010

c51

1500-01040

c52

1500-01040

c53

1500-01040

c54

1500-01040

c55

1500-01040

C56

1540-01060

c57

1540-01060

C58

1500-01040

c59

1540-01060

CAP POL.O47,,F 20% 260” MKT1616
CAP CER .I pF-20%+60% 60”
CAP VAR 5-I 8PF DV, 1 PSIBA
CAP CER .1 ,,F-20%+60% 5OV
CAP MICA 3 pF 10% 500V
CAP CER .I pF-20%+80% 50V
CAP MICA 62 pF 10% 500V
CAP CER .l lrF-20%+80% 50V
CAP CER .I uF-20%+60% 50V
CAP CER .I ;tF-20%+80% 6OV
CAP CER 10 “F 20% 50V
CAP CER .I uF-20%+60% 50V
CAP MICA 6i pF 10% iOOV
CAP CER .I &F-20%+80% SOV
CAP CER 100 pF 20% 50V
CAP CER 100 DF 20% 5OV
CAP CER .l &20%+60% 50V
CAP CER .I ,tF-20%+80% 50V
CAP CHIP .I pF SOV
CAP TANT 10 pF 25V
CAP CER .I ,,F-20%+80% 50V
CAP CER 100 pF 20% 50”
CAP POL.047 pF 20% 260V MKT1816
CAP CER .I pF-20%+60% 5OV
CAP VAR 5-I 6 pF DVI 1 PSI 8A

CAP CER .l )rF-20%+60% 50V
CAP MICA 3 pF 10% 500V

CAP CER .l ,&F-20%+60% 50V
CAP MICA 62 pF 10% 5OOV
CAP CER ., !tF-20%+60% 6OV
CAP CER .I PF-20%+80% 50V
CAP CER .1 uF-20%+80% 50V

CAP CER IO nF 20% SOV
CAP CER .I ,rF-20%+60% 50V
CAP MICA 62 pF 10% 500V
CAP CER .I >lF-20%+80% 5OV
CAP CER 100 pF 20% 50V
CAP CER 100 pF 20% 50V
CAP CER .I pF-20%+80% 50V
CAP CER .I ,,F-20%+80% 50V
CAP TANT 10 ,,F 25V
CAP CHIP .I k,F 5OV
CAP CER .I pF-20%+80% 50V
CAP CER 100 pF 20% 50V
CAP CER ., bF-20%+60% 50V
CAP CER .I pF-20%+60% 50V
CAP CER .I pF-20%+80% 50V
CAP CER .I fiF-20%+80% 50V
CAP CER .I pF-20%+60% 6OV
CAP TANT IO UF 25V
CAP TANT 10 ,,F 25V
CAP CER .I eF-20%+60% SOV
CAP TANT IO pF 26V

,540-o, 060

C60

C6, NOT USED
C65 1500-01040

1500-01040

C66
037 1560-01040

1560-01040

C68
C69’ 1500-01040

1500-01040

c70
c71 1500-04R70

1500-01010

C72
c73 1560-01040
c74 1500-01040
c75 1500-01040
C76 1500-01040
c77 ,560.01040
C78 1560-01040
C7S 1500-01040

1500-01040

C80
CSI 1500-01040

1500-01040

C82
CS3 1500-01040
CS4 1500-01040
C65 1500-01040
C86 1500-01030

C67 1532-01070

c90 1500-01040
C91 1500-01040
c92 1540-01050
c93 1500-01040
CS4 1500-01040
c95
C96 1500-01040
c97 1500-01040
C96
c99
Cl00
Cl01 1500-01040
Cl02
Cl03 1540-01060
Cl04 1540-01060
Cl05 ,533.01060
Cl06 1533-01080
Cl 07 1533-01070
Cl08 1533-01070
Cl09
Cl10
Cl11
Cl12 1500-01040

Cl13 1500-02210
c114
C115 1500-01030
Cl16 1532.04770

Cl 20’ 1500-01040

151 O-02200

C88
C89 1533-01080

,500-o, 040

1500.01040

1500-01040

1500-01040

1500-01040

1532-01090
1532-01090

1532.04770

1500-02210

CAP TANT 10 pF 25V
CAP CER .I pF-20%+60% 50V

CAP CER .I ,,F-20%+60% 50V
CAP CHIP .I ,,F 50V
CAP CHlP ., pF 50V
CAP CER .I pF-20%+80% 50V
CAP CER .I pF-20%+80% 5OV

CAP CER 4.7 pF 20% 5OV
CAP CER 100 pF 20% 50V
CAP CHIP .1 &rF 50V
CAP CER ., @20%+60% 5OV
CAP CER .I ,,F-20%+80% 50V
CAP CER .I ,,F-20%+80% 50V
CAP CHIP .I ,,F SOV
CAP CHIP .I k&F 50V
CAP CER .I ,rF-20%+80% 5OV
CAP CER ., pF-20%+60% 50V

CAP CER .1 ,,F-20%+80°b 50V
CAP CER ., ,d-20%+60% 50V
CAP CER .I ,rF-20%+60% 50V
CAP CER .I ,,F-20%+80% SW

CAP CER .I ,,F-20%+80% 50V
CAP CER 10 nF 20% 50V
CAP ELEC 100 ,I 16V

CAP MlCA 22 pF 20% 50V
CAP ELECTR 1000 b,F/25V

CAP CER .I ,&20%+60% 50V
CAP CER .I ,,F-20%+60% 5OV
CAP TANT 1 pF/25V
CAP CER .I ,rF-20%+80% 5OV
CAP CER .I FF-20%+80% 50V
CAP CER .1 ,,F-20%+60% 50V
CAP CER .I pF-20%+80% 5OV
CAP CER .I pF-20%+80% 50V
CAP CER .1 rrF-20%+80% 50V

CAP CER .1 ,,F-20%+60% 5OV

CAP CER .I ,,F-20%+80% 5OV

CAP CER .I rrF-20%+60% 50V
CAP CER .I ;F-20%+80% 50V
CAP TANT 10 rrF 25V
CAP TANT 10 ;tF 25V
CAP ELECTR 1000 ,,F/25V
CAP ELECTR 1000 &,F/25V
CAP ELECTR lOO~tF125V
CAP ELECTR 10O~Fl25V
CAP ELEC lO.OOO,~F 16V
CAP ELEC lO.OOOpF 16V
CAP ELECTR 470 pF/16V
CAP CER ., pF-20%+80% 50V
CAP CER 220 pF 20% 50V
CAP CER 220 pF 20% 50V
CAP CER 0.0, pF=20%+80% 50V
CAP ELECTR 470 pF/,GV
CAP CER .1 ,,F-20%+60% 5OV

8-2

Table 8-l. h<odel 776 PARTS LIST-MAIN BOARD ..lSSi5MllLl; (CO~rTI!Vl’k’l~)

-

DWG PART
REF NUMBER DESCRIPTION

C121’ 1540-01060 CAP TANT 10 ,,F 26”
C, 22’ 1540-01060 CAP TANT 10 ,,F 25V
C123’ 1500-01040 CAP CER .I pF-20%+80% 5OV
C124’ 1550-01800 CAPVAR5-18pFDVllPS18A
Cl25 SELECTED VALUE
C126’ 1550-01000 CAP VAR 2-10 pF JACKS 5750
Cl27 1500-01040 CAP CER .1 uF-20%+60% 5OV
Cl 28 1500-01040
Cl29 NOT USED
Cl 30 1560-01040
Cl31 1560-01040
Cl33 1500-01040
Cl34 1560-01040
CR1 0300-00400

CR2 0301-10000
CR3 0300.20400
CR4 0300-20010
CR5 0300-10300

CR5

0300-10300
CR6 0300-10300 CR6 0300-10300
CR7 0300-10300 CR7 0300-10300
CR8 0300-10300 CR8 0300-10300
CR9 0300-00400 CR9 0300-00400
CR10 CR10 0301-10000 0301-10000
CR1 1 CR1 1 0300-20400 0300-20400
CR12 CR12 0300-20010 0300-20010
CR13 CR13 0300-10300 0300-10300
CR14 CR14 0300-10300 0300-10300
CR15 CR15 0300-10300 0300-10300
CR16 CR16 0300-10300 0300-10300
CR1 7 CR1 7 0300-21100 0300-21100
CR16 NOT USED

CR16 NOT USED
CR19 NOT USED CR19 NOT USED
CR20 NOT USED CR20 NOT USED

CR21 NOT USED CR21 NOT USED
CR22 NOT USED CR22 NOT USED
CR23 0300-00400 CR23 0300-00400
CR24 NOT USED CR24 NOT USED
CR26 0300.60100

CR26

0300-50100
CR26 0300-30000 CR26 0300-30000
CR27 0300-30000 CR27 0300-30000
CR26 CR26 0300-50200 0300-50200
CR29 0300-90300 CR29 0300-90300

CR30 CR30 0300-90300 0300-90300
CR31 CR31 0300-00400 0300-00400
CR32 CR32 0300-00400 0300-00400
CR33 NOT USED CR33 NOT USED
CR34 NOT USED CR34 NOT USED
CR35’ CR35’ 0300-00400 0300-00400
CR36’ CR36’ 0300-00400 0300-00400
CR37 CR37 0300-90700 0300-90700

DLl 0600-10000
Jl 3000-30260
J2 3000-40120
J2 6800.50500

3000.40300

J2

Kl 0900-01100

CAP CER .t PF-20%+60% 5ov

CAP CHIP .l ,rF SOV
CAP CHIP .I pF 50V
CAP CER .I *F-20%+80% 50V
CAP CHIP .l PF 50V

DIODE Sl lN4151

DIODE PIC AMP PAD 50

DIODE ZENER 1 N758A IOV

DIODE ZENER lN751A 5.1V
DIODE 2835-MATCHED WITH CR6
DIODE 2835-MATCHED WITH CR5
DIODE 2635-MATCHED WITH CR6
DIODE 2835-MATCHED WITH CR7
DIODE Sl lN4151
DIODE PIC AMP PAD 50
DIODE ZENER lN758A IOV
DIODE ZENER lN751A 5.1V
DIODE 2835. MATCHED WITH CR14
DIODE 2835 -MATCHED WITH CR13
DIODE 2835. MATCHED WITH CR16
DlODE 2835. MATCHED WITH CR15
DIODE REF 1 N825A

DIODE Sl lN4151

DIODE BRIDGE WSO05

DIODE RECT 1 N4003
DIODE RECT 1 N4003
DIODE BRIDGE KBL-005 5A GI
DIODESA-5A

DIODESA-5A
DIODE SI IN4151
DIODE 81 1 N4151

DIODE SI lN4151
DIODE Sl lN4151
DIODE 1 N5225

DELAY LINE 7 ns 0402-0007-93
CON MALE 2X10 BERG
CON 24PIN FOR SOLDER
FLAT CABLE 24 PIN
CON GPIB 60924F MONO-8007

RELAY DUAL INLINE IA 5V-6007

DWG PART
REF NUMBER

::

0900-01100 0900-01000

K4

0900-01100

K5

0900-01100

K6

0900-01100

K7

0900-01000

K8

0900-01100

LKlA

3000-40810

LKl B

3000-40610

01

0400-00300

Q2

0400-40700

03

0400-40600
0400-00700

:i

0400-00700

Q6

0400-00300

Q7

0400.40700

Q8

0400-40800
0400-00700

EO

0400-00700

a11

0400-01340
0400-01340

Q12

Q13

0400-01340

Q14

0400-01200

Q15

0400-01200

Q16

NOT USED

Q17

NOT USED

Q16

NOT USED

QIQ

NOT USED

Q20

0400-01810

Q21

0400-00300

Q22

NOT USED
0400-00300

Q23
Q24

0400-00300

Q25

NOT USED

Q28

NOT USED

Q27

NOT USED

Q28

NOT USED

Q29

NOT USED

Q30

0400-40100

Q31

0400-40300

Q32

0400-01500

Q33

0400-40400

Q34

0400-01200

Q35

0400-01200

Rl

0104.10008

R2

0104-10008

R3

0104.9003A

R4

0104-9003A

R5

0104-10030

R8

0100-01540

R7

0100-03300

R6

0100-01510

RQ

.-

0100-01080

RlO

0100-04710

RI 1

0100-01030

RI2

0100-03300

R13

0100-03910

DESCRJPTJON

RELAY DUAL INLINE 1A 5V-6007
RELAY DUAL INLINE 1C 5V-6007
RELAY DUAL INLINE IA 5V-6007
RELAY DUAL INLINE 1A 5V-6007
RELAY DUAL INLINt IA SV-6007
RELAY DUAL INLINE 1C 5V-6007
RELAY DUAL INLINE 1A S/-6007
(‘) CON JUMPER X2
(‘) CON JUMPER X2

TSTR NPN 2N4124
TSTR 2N4418A(SELECTED)
TSTR MRF 904
TSTR NPN 2N5179
TSTR NPN 2N5179
TSTR NPN 2N4124
TSTR 2N4415A (SELECTED)
TSTR MRF 904
TSTR NPN 2N5179
TSTR NPN 2N5179
TSTR 2N3906A
TSTR 2N3906A
TSTR 2N3906A
TSTR 2N3904A
TSTR 2N3904A

TSTR 2N4401
TSTR NPN ZN4124

TSTR NPN 2N4124
TSTR NPN 2N4124

TSTR 2N2219A
TSTR MJE 2955A
TSTR PNP 2N2905A
TSTR MJE 3055
TSTR 2N3904A
TSTR 2N3904A

RES MTF 100 1% 1W
RESMTFlOOl%lW
RES MF QOOK 1% 1/2W
RES MF QOOK 1% 1/2W
RES MF 1OOK 1% 1/4W
RES COMP 150K 5% 1/4W
RES COMP 33 5% 1/4W
RES COMP 150 5% 1/4W
RES COMP 10M 5% 114W
RES COMP 470 5% 1/4W
RES COMP 10K 5% 114W
RES COMP 33 5% 1/4W
RES COMP 390 5% 114W

8-3

Ports Lisl

Table

8-1. Model 776 P.4RTS LIST - nlilIN BOARD ASSEMBLY /CONTINUl?D)

DWG PART
REF NUMBER

0100-01510

R14

0100-07520

R15

0100-01520

R16

010686530

RI7

0100-01810

R18

0100-02720

RlQ

0100-03920

R20
R21

0104-66610
0104-l 0030

R22

0104-28010

R23

0104-28010

R24
R2S

0104-l 0000
0104-10020

R28

0104-15020

R27

010410010

R28

0104.20020

R29

0104-10010

R30

0100-03900

R31

0100-03300

R32

01044R020

R33
R34

0104-30100
0104-11310

R35

0100-02210

R36
R37

0100-03310
0100-02220

R38
R39

0104-l 1030

R40

0104-10008

R41

0104-10008
0104-9003A

R42

0104-9003A

R43

0104-10030

R44

0100-01540

R45

0100-03300

R46

0100-01510

R47
R48

0100-01060
0100-04710

R49

R50

0100-01030
0100-03300

R51

0100-03910

R52
R53

0100-01510

R54

0100-07520
0100-01520

R55
R56

0104-66530
0100-01810

R57

0100-0270

R56
R59

0100-03920
0104-66610

R80

0104-10030

R61

0104-26010

R62

0104-26010

R63
R64

0104-10000

R65

0104-10020

R66

0104-I 5020

R67

0104-20020

R66

0104-10010

R69

0104-10010

R70

0100-03900

R7l

0100-03300
0104-4R020

R72

DESCRJPTJON

RES COMP 150 5% 114W
RES COMP 7.5K5% 1,4W
RES COMP 1.5K 6% 114W
RES MF 865K 1% 1/4W
RES COMP 180 5% 1/4W
RES COMP 2.7K 5% 1/4W
RES COMP 3.9K 5% 1/4W
RES MF 8.68K 1% 1,4W
RES MF IOOK 1% 114W
RES MF 2.8K 1% 1/4W
RES MF 2.8K 1% 1/4W
RES MF 100 1% l14W
RES MF 10K 1% 114W
RES MF 16K 1% 114W
RESMFlK1%1/4W
RES MF 20K 1% ,/4W

RESMFIK1%1,4W
RES COMP 39 5% 1/4W

RES COMP 33 5% 1/4W
RES MF 4.02 1% 1/4W
RES MF 301 1% 1/4W
RESMFl.l3K1%1/4W
RES COMP 220 5% 1/4W
RES COMP 330 5% 1,4W

RES COMP 2.2K5% l/4W
RESMTF110Kl/4Wl%
RESMTFfOOl%lW
RES MTF 100 1% 1W
RES MF QOOK 1% 1/2W
RES MF QOOK 1% 1,2W
RES MF 1OOK 1% 114W
RES COMP 150K 5% 1/4W
RES COMP 33 5% 1/4W
RES COMP 160 5% 114W
RES COMP 10M 5% 114W
RES COMP 470 5% 1,4W
RES COMP lOK5% 1/4W
RES COMP 33 5% 1/4W
RES COMP 390 5% 1,4W
RES COMP 150 6% 1/4W
RES COMP 7.5K5% 114W
RES COMP 1.5K5% 1/4W
RES MF 685K 1% 1/4W
RES COMP 180 5% 1,4W
RES COMP 2.7K6% 114W
RES COMP 3.9K 5% 1,4W
RES MF 8.66K 1% 1,4W
RES MF 1OOK 1% 1/4W
RESMF2,8Kl% 1/4W
RESMF2,6Kl%1,4W
RES MF 100 1% 1,4W
RESMF lOKl% 1/4W

RESMF 15Kl% ,,4W
RES MF 20K 1% ,,4W
RESMF lK,% 114W
RESMF lK,% ,,4W
RES COMP 39 5% 1/4W
RES COMP 33 5% 1/4W
RES MF 4.02 1% 114W

DWG PART

REF NUMBER

R73

0104-30100

R74

0104-11310

R76

0100-02210

R76

0100-03310

R77

0100-02220

R76

0104-11030

R79

0100-06210

R60

0203-02020

R81

0203-02020

R82

0203-01030

R83

0203-01030

R64

0203-02020

R85

0203-02020

R87

NOT USED

R88

NOT USED

R89

NOT USED

RQO

0100-05110

RQl

0100-01020

R92

0100-05110

R93

0100-05110

R94

0100-02410
R95 0100-05110
R96 0100-03310
R97 0100-02720

R98 0100-02220
RQQ 0100-03310
RIO0 0100-05110
RI01 0100-05110
R102 0100-06600
RI03 0100-02010
R104 0100-08800
R105 0100-05110
R106 0100.01220

R107 0100-01020
R108 0100-05110
RI09 0100-05110
RllO OlOO-05110
Rlll 0100-03310
RI 12 0100-02410
R113 0100-01010
R114 0100-05110
RI 15 0100-03310
R116 0100-07520
R117 0100-03310
Rll6 0100-05120
R119 0100-05110
R120 0100-05110
R121 0100-02720
R122 0100-05110
R123 0100-02220
R124 0100-05110
R125 0100-05110
RI26 0100-05110

R127 0100-05110
R128 0100-05110
RI29 0100-05110
RI30 0100-05110
RI31 0100-05110
R132 0100-05110

DESCRJPTJON

RES MF 301 1% 1/4W

RES MF l.l3Kl% 114W
RES COMP 220 5% lI4W
RES COMP 330 5% ll4W
RES COMP 2.2K 5% 1/4W
RESMTFllOK1/4Wl%
RES 620 1/4W5%
RES VAR 2K 3386F-l-202
RES VAR 2K 3386F-1.202
RES VAR 10K 3366F.l-103
RES VAR 10K 3386F-I-103

RES VAR 2K 3386F-l-202
RES VAR 2K 3386F.l-202

RES COMP 510 5% 1/4W
RES COMP 1 K 5% 114W
RES COMP 510 5% lI4W
RESCOMP5105% 1/4W
RES COMP 240 5% 1/4W
RES COMP 510 5% 1/4W

RES COMP 330 5% 1/4W
RES COMP 2.7K 5% 1/4W
RES COMP 2.2K 5% 1/4W
RES COMP 330 5% 1/4W
RES COMP 510 5% lI4W
RES COMP 510 5% 1/4W
RES COMP 68 5% 114W
RES COMP 200 5% 1/4W
RES COMP 86 5% 1/4W
RESCOMPBlOW 1/4W
RES COMP 1.2K5% 1/4W
RES COMP 1 K 6% 1/4W
RES COMP 510 5% 1/4W
RES COMP 510 5% 1/4W
RES COMP 510 5% 1/4W
RES COMP 330 5% ll4W
RES COMP 240 5% 1/4W
RES COMP 100 5% 114W
RES COMP 510 5% 114W
RES COMP 330 5% 1/4W
RES COMP 7.5K 5% 1/4W
RES COMP 330 5% 1/4W
RESCOMP5,1K5%1/4W
RES COMP 510 5% 114w

RES COMP 510 5% 114W

RES COMP 2.7K 5% 1/4W

RES COMP 510 5% 1/4W
RES COMP 2.2K 5% 1,4W
RES COMP 510 5% 114W
RESCOMP5105%1/4W
RES COMP 510 5% 114W
RES COMP 510 5% 114W
RES COMP 510 5% 114W
RES COMP 510 5% 1/4W
RES COMP 510 5% 1/4W
RES COMP510 5% 114W
RES COMP 510 5% 1/4W

83

Table 8-1.

Model 776 PARTS LIST-h&UN BOARD ASSEhfBL)~ (CONTINUED)

DWG PART
REF NUMBER

R133 0100-05110
R134 0100-07520
RI35 0100-05110

RI 38 0100-07520
R137 0100-01030
RI36 0100-01020
R139 0100-02720
R140 0100-06210
R141 0100-06210
R142 0100-01030
RI43 0100-01510
RI44 0100-08210
R145 0100-02020
RI48 0100-03310
RI47 0100-01030
R148 NOT USED
RI49 NOT USED
RI50 0100-5110
R151 0100-01020

R152 NOT USED
RI53 NOT USED
RI54 0100-01020
RI55 0100-01020
RI58 0100-01030
RI 57 0100-01020
RI58 0100-03310
RI59 0100-01020
R180 0100-03310
RI 66 0100-03320
RI67 0100-01030
RI 66 0203-01010
RI89 0104-12100
RI70 0104-10010

R171 NOT USED
R172 0100-01010
R173 0100-01520
RI 74 0100-02730.

DESCRIPTION

RESCOMP5105%1,4W

RES COMP 7.6K 5% ,,4W
RES COMP 610 5% ,,4W
RES COMP 7SK5% 1/4W
RES COMP lOK5% 114W
RESCOMPlK5%1/4W
RES COMP 2.7K 5% 1,4W
RES COMP 620 5% 1,4W
RES COMP 620 5% 1/4W
RES COMP 10K 5% 114W
RES COMP 150 5% 1/4W
RES COMP 820 5% 114W
RES COMP 2K5% 114W
RES COMP 330 5% 114W
RES COMP lOK5% 114W

RES COMP 510 5% 1/4W
RES COMP 1 K 5% ,,4W

RESCOMP lK6% 114W
RESCOMPlK5%1/4W
RES COMP IOK 5% 1/4W
RESCOMPlK5%1/4W
RES COMP 330 6% 114W
RESCOMPlK5%1/4W
RES COMP 330 5% 114W
RES COMP 3.3K 5% 114W
RES COMP lOK5% 1/4W
RES VAR 100 3388F-l-101
RESMF 121 1% 1/4W
RESMFlkl%1/4W

RESCOMP 1006% ,,4W
RES COMP 1 .SK 6% 1,4W
RES COMP 27K5% 1/4W

RESCOMP lK5% 1/4W
RES COMP 120 5% 1/4W
RES COMP 4.7K5% 114W
RES MF 5.76K 1% 114W
RESCOMP lK5% 1/4W
RESCOMPl205%1/4W
RES COMP 1 K 5% 1,4W
RES MF 8.86K 1% 1/4W
RES MF 8.04K 1% 1/4W
RESMFIOK1%1/4W
RESVARlK3368F.l-102
RES COMP 220 5% 1/4W
RES COMP 220 5% ,,4W
RES COMP 1.6K 5% 1/4W
RES COMP 580 6% 1/4W
RESCOMPlK5%1/4W
RESCOMPlKB% 1,4W
RES COMP ,.6K5% l14W

DWG PART
REF NUMBER

R201 0100.02R70
R202 0100.02R70
R203 0102-03300

RN1

0109.01500

RN2

0111-01038
01 IO-01 03c CSC 05A-01.103Y 4XlOK/5 PIN

RN3
RN4

0110-05118

SPl

0900-01900 BEEPER AT-02

SW1

2000-I 0800 BWON-OFF FOR 775

0540.01100

Ul
u2

0500-l 1800

0540-01100

I

0580-00700

u5

0500-58500
0540-01100

U6
“7

0540-01100

U6

0580-00700

u9

0500-56500

IJIO

0500-53400

Ull

0500-53400

u12

0500-80500

u13

0540-01100

u14

0540-01100

u15

0540-01100

U18

0540-00830

“17

0500-45300

UIS

0500-40910

UIQ

0500-40910

u20

0500-40900

lJ21

0500-45000

u22

0500-45300
0500-12800

U23

0500-46400

U24
Ll25

0500-40900

U28

0500-40900

U27

0500-41200

U26

0500-45000

U29

0500-45300

U30

0600-46300

u31

050040920

u35

0500-I 1800

U38

0500-20700

U37

0540.00830

u3s

051 o-02700

u39

0500-21420

lJ40

051 o-03650
0520-07000

u41
U42

0500-21230 EPROM 27258
0500-q ,180 MK48202B-20 MOSTEK

u43
U44

0550-00100 32EIT BINARY COUNTER LS7081

u45

0550-00100 32BlT BINARY COUNTER LS7081
U48
u47 0500-21300

0500-21510 BUFFER FOR GPIB DS75180N

U48
u49 0500-21520
u50 0500.52200 VOLTAGE REGULATOR MC7612CP
“51 0500.52300 VOLTAGE REGULATOR MC7912CP

DESCRIPTION

RES COMP 2.7 5% ll4W
RES COMP 2.7 5% ll4W
RES COMP 33 5% 1/8W 882205

RES NET MDP-16-03.150G 15118
RES NET lOWlO MSP-IOA-Ol-103G

CSC 05A-01.511Y 4X510/5 PIN

6 BIT SHIFT REGISTOR CD40946
BUFFER 9888 (L204)

8 BIT SHIFT REGISTOR CD4094S

D-A 10 BIT CONVERTOR AD7533JN

DUAL OP AMP LM1456N
8 BIT SHIFT REGISTOR CD40948
8 BIT SHIFT REGISTOR CD40946

D-A 10 BIT CONVERTOR AD7533JN

DVAL OP AMP LM1458N
SUPER GAIN OP AMP LN306A
SUPER GAIN OP AMP LN306A
AD 9887 BD
8 BIT SHIFT REGISTOR CD40946
8 BIT SHIFT REGISTOR CD40946
8 BIT SHIFT REGISTOR CD4094B
HEX INVERTOR CD 40498
ECL FLIP-FLOP MClOH13lP
ECLOR/NOR GATE MCl0105P
ECLOR/NOR GATE MC10105P
ECL NOR MC10102P
ECL NOR MC1OH102P
ECL FLI
D-FLIP­ECL X0
ECL NOR MCIOlOZP
ECL NOR MC10102P
ECL FLIP-FLOP MCl013Pl
ECL NOR MClOHl02P
ECL FLIP-FLOP MClOH13lP
ECL FLIP-FLOP MCfOH131P
ECL TO TTL-TTL TRANS MCl0125P
BUFFER 9886 (L204)
KEYBOARD/DISPL.INT. P6279
HEX INVERTOR CD4049B
LOW POWER SCHOTTKY 74LS138
SINGLE CHIP MICROCOMP P6031
LOW POWER SCHOTTKY 74LS373
H-MOS-DEVIDER SN74HC4040

IOW POWER SHOTKEY 74LS393N
G.P.I.B P6291A

BUFFER FOR GPlS DS7518lN

IP-FLOP MClOH131P
FLOP 74F74

R/XNOR MClOH107P

8-5

Table

8-1. Model 776 P;IRTS LIST - .MlI.V BOARD ASSEMBLY (COh’TIAWED)

DWG PART
REF NUMBER DESCRIPTlON

U52 0500-58500 DUAL OP AMP LMl458N
U55(‘) 0500-52000 VOLTAGE REGULATOR MC7605CP
U56(‘) 0510-02800 LOW POWER SCHOTTKY 74LS132

Table

8-2. Model 776 PARTS LIST - 500 MHz MULTIPLIER ASSEMBLI

DWG PART
REF NUMBER

Cl

1500-01040 CAP CER .I pF-20%+80% 50V
1500-01030

c2
c3

1580-01040 CAP CHIP .I pF 50V

c4

1540-01060

C5

1500-01040

C8

1500-01040 CAP CER .I ,,F-20%+80% 50V

c7

1540-01080 CAP TANT 10 pF 25V

C8

1500-01040

CQ

1500-01010

Cl0

1560-01040 CAP CHlP .l p’F 50V

Cl1

1500-01 ROO

Cl2

1580-01040

Cl3

1580-01040

Cl4

1580-01040 CAP CHIP .I ,,F 50V

Cl5

1540-01080

Cl8

1540-01080 CAP TANT 10 ;,F 25V

Cl7

1500-02030 CAP CER 20 nF 20% 50V

Cl6

1500-04720 CAP SCR 4.7 nF 20% 50V

C20

1540-01080 CAP TANT 10 pF 25V

c21

1580-01040 CAP CHIP .l ,,F 50V

c22

SELECTEDVALUE

C23

1580-02200 CAP CHIP 22 pF 50V

C24

1580-02200 CAP CHIP 22 pF 50V

C25

1580-02200 CAP CHIP 22 pF 50V

C28

* SELECTED VALUE

C27

1540-01080 CAP TANT 10 OF 25V

C26

1533-01070 CAP ELECTR iO0 @F,25V

CR1

0300-00400 DIODE SI 1 N4151

CR2

0300-00400 DIODE St 1 N4151

CR3

0300.20700 DIODE ZENER 1 N758A 6.2 V

CR4

NOT USED

CR5

0301-00200 DIODE 1N5445A

J1

3000-30250 CON MALE 2X6

J2

3000-18000 CON RF MALE JACKSON

DESCRIPTION

CAP CER 10 “F 20% 50V

CAP TANT 10 pF 25V
CAP CER .I pF-20%+80% 6OV

CAP CER .I ,,F-20%+80% 50V
CAP CER 100 DF 20% 50V

CAP CER 1 pF
CAP CHIP .1 uF 50V
CAP CHIP .I pF 50V

CAP TANT 10 nF 25V

DWG PART
REF NUMBER DESCRIPTION

U57(‘) 0600-50000
U56(‘) 0510-00110
U59(-) 0580-00900

Yl 0600-30000 CRYSTAL 18MHZ C.T.S

OSCILLATOR IOMHZ SPPM
LOW POWER SCHTTKY 74LSO2
DIGITAL TO ANALOG CONVAD8875

DWG PART
REF NUMBER DESCRIPTION

Jl

3000-30520

Ll

0800-03330

L3

4200-00000

LK1

3000-30200

LK2

3000-30200

LK3

3000-30200

R,

0100-01010
0100-01620
0100-05810

R4

0100-05810

R5

0100-05610

R8

0100-01030

R7

0100-04720

R6

0100-01220

RQ

0100-02040

RIO

0100-01020

Rll

SELECTED VALUE

R12

0100-01020

R13

0100-03330

RI4

0100-01030

RI5

0100-02220

RI8

0100-02220

RI7

0101-05810

Rl8

0113.01000

RI9

0101-02010
0510-02800

i:

0540-01800

“3

0500-57400

U4

0500-84300

“5

051 o-02400

“6

0500-57200
0500-58310

u”;

0500.90900

UQ

0400-20500

UlO

0600-90000

Llll

0500-52000

CON FEMALE 2X6-6200
COIL 3.3 fiH 1537-24

2X FERR BEAD CERAMAG24 57-1355
3 X CON BERG 75160-315 (1 PIN)

3 X CON BERG 75180-315 (1 PIN)
3 X CON BERG 75180-315 (1 PIN)

RESCOMPl005%1,4W
RES COMP 1.6K 5% 1/4W
RES COMP 580 5% 114W
RES COMP 580 5% 114W
RES COMP 580 5% 114W
RES COMP 10K6% 1,4W
RES COMP 4.7K 5% 1/4W
RES COMP 1.2K 5% 114W
RES COMP 200K 5% 1/4W

RES COMP IK 5% 1/4W
RES COMP 1 K 5% 1,4W

RES COMP 33K5% 114W
RES COMP lOK5% 114W
RES COMP 2.2K 5% 1/4W
RES COMP 2.2K 5% 114W
RES COMP 580 5% 112W
RES CHIP IO 5%
RES COMP 200 5% 1/2W
LOW POWER SCHOTTKY 74LSl32
PHASE DIDECTOR MC4044 18 PIN
PRESCALER DIVIDER:4 CA3199E
SP8829
LOW POWER SCHOTTKY 74LS93

BI-MOS OP-AMP CA3140E
OP AMP LM741 C
ANALOG SW DG211 CJ
MAR 3
TCXO 1OMHZ 1 PPM -OPTION 51
VOLTAGE REGULATOR MC7805CP

Table

8-3. Model 776 PARTS LIST FRONT PANEL ASSEMBLEY

DWG PART
REF NUMBER DESCRIPTION

CR1 0300-00400
CR2 0300-00400 DIODE SI IN4151
CR3 0300-00400 DIODE SI 1 N4151

DSl
TO

1200-10600

DS9
DSIO 1200-10100

DSII 1200-10200
DS12

TO
DSIB 1000-00300

DSl9
TO
DS41 1000-00700
DS42 1200-10600
J4 3000-40150

Ql
TO
Q14 0400-01800 TSTR PNP2N4403

DIODE SI 1 N4151

7 SEGMENT LED DISPLAY MDSP5501
LED HDSP 7507 +/- 16020

LED HDSP 7501 7 SEG 776

MINI 3MM LED RED 5082-4460

LED RED MV 57124-16 G.I
7 SEGMENT LED DISPLAY
CON 20 PIN MALE FOR SOLDER

MDSP5501

DWG PART
REF NUMBER

RI

0100-02210

R2

0100-02210

R3

0100-02210

R4

0100-02210

RS

0100-02210

R6

0100-02210

R7

0100-02210

R8

0100-02210

R9

0100.02210

RIO

0100-02210

RI1

0100-02210

R12

0100-02210

RI3

0100-02210

RI4

0100-02210

RI5

0100-02700

RI6

0100-02200

R99

0100-02210

Sl
TO
S16

2000-61600

“1

051 o-02700

“2

051 o-02700

DESCRIPTION

RES COMP 220 5% 114W
RES COMP 220 5% 1/4W
RES COMP 220 5% 114W
RES COMP 220 5% 114W
RES COMP 220 5% 1/4W
RES COMP 220 5% 114W
RES COMP 220 5% 1/4W
RES COMP 220 5% 1/4W
RES COMP 220 5% ll4W
RES COMP 220 5% 114W
RES COMP 220 5% 114W
RES COMP 220 5% 1/4W
RES COMP 220 5% 114W
RES COMP 220 5% 1/4W
RES COMP 27 5% ll4W
RES COMP 22 5% 114W
RES COMP 220 5% 1/4W

SWC PUSH MOMENTARY
LOW POWER SCHOTTKY 74LS138

LOW POWER SCHOTTKY 74LS138

Table

8-d. Model 776 P.4RTS LIST - 2.4 GHZ I:VPlJTASSEMBLt

DWG PART
REF NUMBER DESCRIPTION

Cl

1560-01020 CAP CHIP ,001 fi 50V
1560-01020

c2
c3 1560-01020 CAP CHIP ,001 p 50V
c4 1560-01020

1560-01020

c5
C6 1560-01020
c7 1560-01020 CAP CHIP .OO, ,I SOV
C8 1560-01020
C9 1560-01020
Cl0 1560-01020
Cl1 1560-01020
Cl2 1560-01020

1560-01020

ci3

1560-01020

Cl4
Cl5 1560-01020
Cl6 1560-01000
Cl7 1560-01020

1560-01020

Cl8
Cl9 1560-02200

1560-01040

c20

1560-01040

c21
c22 1560-01040

CAP CHIP ,001 p 50V

CAP CHIP ,001 p 50V
CAP CHIP ,001 p 50V
CAP CHIP ,001 ,I 50V

CAP CHIP ,001 p 5OV
CAP CHIP ,001 $SOV
CAP CHIP ,001 p 5OV
CAP CHIP ,001 p 50V
CAP CHIP ,001 ,, 50V
CAP CHIP ,001 ,, 50V
CAP CHIP ,001 p 50V
CAP CHIP .OOl p 50V
CAP CHIP 10 pF 50V
CAP CHIP ,001 p 50V
CAP CHIP ,001 p 50V
CAP CHIP 22 pF 50V
CAP CHIP .I r,F 50V
CAP CHIP .I ,,F 50V
CAP CHIP .I pF 50V

DWG PART
REF NUMBER

CR1

0300-10300

CR2

0300-10300

CR3

0300-10300

CR4

0300-10300

CR5

0300-10300

CR6

0300-10300

CR7

0300-10300

CR8

0300-10300

CR9

0300-10300

CR10

0300-10300

CR1 1

0300-10300

CR12

0300-10300
CR13 0300-10300
CR14 0300-10300
CR15 0300-10300

J1 3000-30250

RI 0113-05100
R2

0113-05100

R3 0100-02020
R4

0100-02020

DESCRIPTION

DlODE HOT CARRIER 5062-2635
DlODE HOT CARRIER 5062-2835
DlODE HOT CARRIER 5082-2835
DlODE HOT CARRIER 5082-2835
DlODE HOT CARRIER 5082-2635
DlODE HOT CARRIER 5062-2835
DlODE HOT CARRIER 5062-2835
DlODE HOT CARRIER 5082-2835
DIODE HOT CARRIER 5062-2635
DlODE HOT CARRIER 5082-2635
DIODE HOT CARRIER 5082.2635
DlODE HOT CARRIER 5082-2635
DIODE HOT CARRIER 5062.2835
DlODE HOT CARRIER 5082-2635
DlODE HOT CARRIER 5082-2835

CON MALE 2X8

RES CHIP 51 5%
RES CHIP 51 5%
RES COMP 2K 5% 114W
RES COMP 2K 5% 1/4W

8-7

Table

8-4. Model 776 PARTS LIST - 2.4 GHZ INPUTASSEARLY ICONTINUED)

DWG PART
REF NUMBER DESCRIPTION

R5

0100-03910

R6

0100-03910

R7

0100-03910

R8 0100-01020
R9 0100-01540
RIO

0100-01020

RI1

0100-01540

R12 0100-01020

R13 * SELECTED VALUE
RI4 0100-02250
RI5

0100-03310

RI6

0100-02710

RES COMP 390 5% 114W
RES COMP 390 5% 1/4W
RES COMP 390 5% 1,4W

RES COMP lK5% 1,4W

RES COMP 160K5% 1,4W
RESCOMPlK5%1/4W
RESCOMP150K5%1/4W

RES COMP lK5% 1/4W
RES COMP 2.2M 5% 1,4W

RES COMP 330 5% 1/4W
RES COMP 270 5% 1/4W

DWG PART
REF

NUMBER

RI7

0100-08210

RI8

0113-03010

R19

0113-03300

R20

0113-03010

R21

0113-03010

R22

0113-03010

R23

0100-01020

Ul

0400.20600

u2

0400-20600

u3

0400-20600

“4

0500-64400

U5

0500-53700

DESCRIPTION

RES COMP 620 5% 1/4W
RES CHIP 300 5% 1/8W
RES CHIP 33 6% 1/8W
RES CHIP 300 5% l/SW
RES CHIP 300 5% 1,6W
RES CHIP 300 5% l/BW
RESCOMPlK5%1/6W
MAR-7 MINI CIRCUITS
MAR-7 MINI CIRCUITS

MAR-7 MINI CIRCUITS

U.P.S. 5880 - NEC
LM393N

x-x