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