Tektronix 775A Instruction Manual

Instruction Manual

Model 775A

Programmable Counter / Timer

©1987, Keithley Instruments, Inc.

All rights reserved.

Any unauthorized reproduction, photocopy, or use the information herein, in whole or in part, without the prior written approval

of Keithley Instruments, Inc. is strictly prohibited.

All Keithley Instruments product names are trademarks or registered trademarks of Keithley Instruments, Inc.

Other brand names are trademarks or registered trademarks of their respective holders.

Cleveland, Ohio, U.S.A.

Document Number: 775-901-01 Rev. B / February 1987

WARRANTY

Keithley instruments, Inc. warrants this product to be free from defects
in material and workmenship for a period of 1 year from date of ship­ment. 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 represent-

ative, or contact Keithley headquarters in Cleveland, Ohio. You will be
given prompt assistance and return instructions. Send the instrument,
transportation prepaid, to the indicated service:facility. Repairs will be
made and the instrument returned, transportation prepaid. Repaired
products are warranted for the balance of the original warranty period,
or at least 90 days.

LIMITATION OF WARRANTY

This warranty does not apply to defects resulting from unauthorized
modification or misuse of any product or part. This warranty also does
not apply to fuses, batteries, or damage from battery leakage.

This warranty is in lieu of all other warranties, expressed or implied, in-

cluding any implied warranty of merchantability or fitness for a par-

ticular use. Keithley Instruments, Inc. shall not be liable for any indirect,
special or consequential damages.

STATEMENT OF CALIBRATION

This instrument has been inspected and tested in accordance with
specifications published by Keithley Instruments, Inc.

The accuracy and calibration of this instrument are traceable to the

National Bureau of Standards through equipment which is calibrated at

planned intervals by comparison to certified standards maintained in
the Laboratories of Keithley Instruments, Inc.

KEITHLEY INSTRUMENTS, INC.
INSTRUMENT DIVISION I 29775 Aurora Road / Cleveland. Ohio 44139 / U.S.A. / 1216) 246-0400 / Telex: 99.5469

WEST QERMANY:

aREA BRITAIN: Keithlay Instruments, Ltd. / 1, Boulton Road / Reading, Berkshire RG 2 ONL / 10734) 66-l 2.67/66 / Telex: 94.7047

FRANCE Keithlsy Instruments SARL / 2, Bis Rue L&n Blum / 9.P. 60 / 91121 P$laiseau Cedex / 16101 l-51 -55 /Telex: 600-933

NETHERLAND%
SWITZERLAND:
AUSTRI*:
ITALY:

Keith@ lnatruments Ges.m.b.H. / Doblinger Haupstr. 32 / 1190 Wien / 314 299 / Telex: 13-4500

Kelthley Instruments, SRL / Viale S. Gimignano 4/A / 20100 Milano, Italy / 4120360

Keithley Instruments GmbH / Heiglhofstr. 5 / 6000 Munchen 70 / 10691 710020 / Telex: 52.12160

Kelthley Instruments BV / Arkelsedijk 4 / Postbus 559 / 4200 AN Gorinchem / 101 1930.25577 / Telex: 24-664

Kelthley Instruments SA / Kriesbachstr. 4 / 9600 Oibendorf / 01/821-94-44 / Telex: 57-536

SPECIFICATIONS

INPUT CHARACTERISTICS
Channel A, B; each channel

RANGE:
SENSITIVITY (d):

DYNAMIC RANGE (xl): 50mV to 5V pk-pk, <ZOMHz.

COUPLING: ac or dc, switchable.
IMPEDANCE: lMR nominal, shunted by <60pF.
ATTENUATOR: xl or xl0 nominal, switchable.
LOW PASS FILTER: -1OdB
SIGNAL OPERATING RANGE (xl): -2.55V dc to t2.55V dc.

TRIGGER LEVEL: -2.55V dc to +2.55V dc, xl.
TRIGGER LEVEL RESOLUTION: lGmV, xl.

TRIGGER LEVEL SElTING ACCURACY:

TRIGGER LEVEL SETTING OUTPUT: via rear panel BNC,
SLOPE: + or - slope, switchable.

DAMAGE LEVEL:

0 to l20MHz, dc coupled.
30Hz to IZOMHz, ac coupled.

25mV rms, <lOMHz.
50mV rms, > 1OMHz.

14OmV to 2.5V pk-pk, >20MHz.

at

1OOkHz nominal, switchable.

:25.5V dc to +25.5V dc, x10.

Mo”v, xx?

*(35mV + 2% of setting), xl.
*(35OmV + 2% of setting), x10

not adjusted for attenuators.

xl: dc-2kHz 250V dc + peak ac

2kHz-100kHz 5 x 1OsV rms*Hz/frequency

> 1OOkHz

x10: dcZOkHz 250V dc + peak ac

20kHz.100kHz 5 x 10%’ rms.Hz/frequency

> 1OOkHz

5v rms

5oV rms

PERIOD A

RANGE:

LSD DISPLAYED: 1Ons to O.lms.
ACCURACY:

Mns to 10” seconds.

*l LSD *(Time Base Error x Period) f Trigger Error.

PERIOD AVERAGE A

RANGE: 1Ons to 10sec.
LSD

DISPLAYED: (10ns x l’eriod)/Gate Time.

RESOLUTION:

fl LSD f

ACCURACY:

NUMBER OF PERIODS AVERAGED: Gate Time/Period

(1.4 x Trigger Error + Zns) x Period

Gate Time

f Resolution *(Time Base Error x Period)

TIME INTERVAL A-B

RANGE: 1011s to

LSD DISPLAYED: 1Ons to O.lms.
ACCURACY: fl LSD *(Time Base Error x Time Interval)

f Trigger Error * Trigger Timing Error -t2ns.

lo4 seconds.

PULSE WIDTH A (Positive or Negative)

RANGE: Mns to lo4 seconds.
LSD DISPLAYED: lOns to O.lms.

ACCURACY: fl LSD *(Time Base Error x Pulse Width)

f Trigger Error f Trigger Timing Error f2ns.

mALIZE A

Channel C (with Model 7751 option)

RANGE: 5OMHz to 1.3GHz.

SENSITIVITY: l5mV, 50MHz to l.OCHz;

25mV, l.OGHz to 1.2GHz;

75mV, 1.2GHz to 1.3GHz
DYNAMIC RANGE: 25mV rms to 1V rms.
COUPLING: ac.

IMPEDANCE: 500.
DAMAGE LEVEL:

dc-100kHz

>.lOOkHz

l5V dc + peak ac

5v rms

FREQUENCY A, B

RANGE: O.lHz to l20MHz.
LSD DISPLAYED: (101~s x Frequency)/Cate Time
RESOLUTION:

*l ,.SD -t (1.4 x Trigger Error + 2ns)x Frequency

Gate Time

ACCL RACY:

*Resolution *(Time Base Error x Frequency)

DIGITS DISPLAYED: 8 per second of Gate Time, minimum.

MODES: Cumulative or A gated by B
RANGE: 0 to lo”-1
REPETITION RATE: lZ0MHz “ax.
LSD DISPLAYED: 1 count up to lOLo-1, then 9 most signifi-

cant digits.

ACCURACY: kl LSD

GATE/DELAY

INTERNAL GATE TIME: Variable from loops to IOsec in 45

increments, or one period of the input, whichever is longer.
May be used in Frequency and Period Average
measurements.

EXTERNAL GATE TIME: Continuously variable from loops

to Klsec, or one period of the input, whichever is longer.

EXTERNAL GATE DELW: 10~s + one period of the

input signal, maximum.

INTERNAL DELAY TIME: Variable from lOO@ to 10s~ in 45

increments. May be used in Period, Time Interval and Pulse
Width measurements.

EXTERNAL DELAY TIME: Continuously variable from loops

to >l hour.

EXTERNAL GATE/DELAY INPUT: Positive TTL signal via

rear panel BNC.

TIME BASE

GENERAL

FREQUENCY: 1OMH.z.
AGING RATE: 55 x lo-‘/month.
TEMPERATURE: f5 x lo-! 0’ to 40°C, ref 25’C.

TCXO (with Model 7752 option)

FREQUENOI: l!&II-Iz
AGING RATE: <l x IO-‘/month.
TEMPERATURE: *I x 10-q 0 to 4O’C, ref 25’C.
LINB VOITAGE: < 1 x lO-’ for 10% change.

IEEE-488 INTERFACE

MULTILINE COMMANDS: DCL, LLO, SDC, Gm, GTL,

UNT, UNL, SPE, SPD.
UNILINE COMMANDS: IFC, RBN, EOI, SRQ, NN.
INTERFACE FUNCTIONS: SHl, AHl, T6, TEO, IA, LEO, SRl,

PPO, DCl, DTI, CO, El.
PROGRAMMABLE PARAMETERS: AI1 front panel controls

(except POWER) plus Reading Rate, Data Format, Trigger,

EOI, Terminator, Service Request, Self Test, Display, Stahu.
READING RATES: one shot, normal (3/second), fast

(ZYsecond), or dump (14O/second).

DISPLAY:
BENCH READING RATES: One shot, or normal (3/second).
ARMING nRIGGER): Each channel is armed by it’s own

signal; or RESET button 01 EXT ARMING input when in one
shot (HOLD) mode.

ARMING DELAY: 30~ in Frequency and Period Average;

lOas in Period, Tie Interval and Pulse Width.

EXTERNAL ARMING INPUT: positive edge ‘IX signal via

rear panel BNC.

EXTERNAL TIME BASE INPUT: lOMHz ‘ITL signal via rear

panel BNC

TIME BASE,OUT: 2V minimum @ MMHz, 1OOD output resis-

tance, via rear panel BNC.
GATE: LED ,indicator lights when gate is open.
WARMUP: 2 hours to rated accuracy and stability
OPERATING TEMPERATURE: 0” to 4O”C, 0% to 80% relative

humidity
STORAGE TEMPERATURE: -25” to 65°C.
POWER: lO?-l25V or 2lO-250V (rear panel switch selected),

50-6OHz. 35VA max. 90-1lOV available.
DIMENSIONS, WEIGHT: l27mm high x 2l5mm wide x

359mm deep (5”~ 8’X’x 14r).

Net weight 3.5kg (8 lbs).

Nine

LED digits with decimal point and exponent.

Specifications subject to change without notice.

TABLE OF CONTENTS

SECTION l-GENERAL INFORMATION

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

INTRODUCTION.
MODEL775 FEATURES
WARRANTY INFORMATION
MANUAL ADDENDA

SAFETY SYMBOLS AND TERMS
INSPECTION
USING THE MODEL 775 MANUAL
ACCESSORIES

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

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

................................................................. l-l

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

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

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

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

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

SECTION Z-BASIC COUNTER/TIMER OPERATION

2.1

2.2

2.2.1

2.2.2

2.2.3

2.2.4

2.3

2.3.1

2.3.2

2.3.3

2.3.4

2.4

2.5

2.5.1

2.6

2.6.1

2.6.2

2.6.3

2.6.4

2.6.5

2.6.6

2.6.7

2.6.8

2.6.9

2.7

2.7.1

2.7.2

2.7.3

2.7.4

2.8

INTRODUCTION
FRONTI’ANEL FAMILIARIZATICJI’J

Controls

Terminals .................................................................................

Display and Indicators
TiltBail

REAR PANELFAMILIARIZATION

Connectors and Terminals

Line Voltage Selector Switch ................................................................

IEEE-488 Address Switches .................................................................

Line Fuse

POWER-UP PROCEDURE ....................................................................

DISPLAYMESSAGES ........................................................................

No Option Message

CONTROL SELECTION

Function

Selecting GateTime .......................................................................

User Gate Function ........................................................................

Using Delay ...............................................................................

User Delay Function ......................................................................

Selecting Measurement Rate
Selecting the Number of Displayed Digits.
Input Condition Controls Setting.,

Setting Trigger Levels

ARMING..

Continuous Arming....................~ ..................................................

Front Panel Arming

External Arming ..........................................................................

Alarm Conditions

APPLICATIONS

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

................................................................................... 2-6

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

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

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

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

..................................................................... 2-6

............................................................ 2-6

.................................................................. 2-6

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

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

............................................................... 2-10

.................................................. 2-10

......................................................... 2-11

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

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

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

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

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

l-l
l-1

l-1

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

2-l
2-4

2-4
2-5

2-6
2-6
2-6
2-6

2-7

...2- 7

2-8

2-8

2-8

2-9

2-9

2-10

2-11
2-12

2.12
2-12
2-13

2-13
2-U

SECTION 3-IEEE-488 OPERATION

3.1

3.2

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .._..._.................................. 3-l

BUS DESCRIPTION . . . . . . . . . . . . . . . . . . .._...............................................,,... 3-l

TABLE OF CONTENTS

3.3

3.3.1

3.3.2

3.3.3

3.4

3.4.1

3.4.2

3.4.3

3.4.4

3.4.5

3.5

3.6

3.6.1

3.6.2

3.6.3

3.7

3.7.1

3.7.2

3.7.3

3.8

3.8.1

3.8.2

3.8.3

3.0.4

3.9

3.9.1

3.9.2

3.9.3

3.9.4

3.9.5

3.9.6

3.9.7

3.9.8

3.10

3.10.1

3.102

3.10.3

3.10.4

3.10.5

3.10.6

3.10.7

3.108

3.10.9

3.10.10

3.10.11

3.10.12

3.1o.u

3.10.14

3.10.15

3.10.16

3.10.17

3.11

3.11.1

3.11.2

3.11.3

3.u.4

3.: A

IEEE-488 BUS LINES . .

Bus Management Lines.. ..................................................................

HandshakeLines ..........................................................................

Data Lines

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

BUS COMMANDS ..........................................................................

Uniline Commands

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

UniversalCommands ......................................................................

Addressed Commands .....................................................................

Unaddressed Commands

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

Device-Dependent Commands .............................................................. 3-5

COMMAND CODES

COMMAND SEQUENCE. ..............................................

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

.< ................... 3-6

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

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

Device-Dependent Command Sequence

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

HARDWARE CONSIDERATIONS ............................................................

Typical Controlled Systems. ................................................................

BusConnections.. ........................................................................

Primary Address Programming ............................................................

:

SOFTWARE CONSIDERATIONS I .............................

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

Controlled Interface Routines ..............................................................

HP-8 BASIC Statements ....................................................................

Interface Function Codes . . .
Model 775 Interface Commandr

GENER,

AL BUS COMMAND PROGRAMMING

;

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

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

REN (Remot e Enable) .....................................................................

IFC (Interface Clear)

LLO‘(Local Lockoui)
GTL (Go To Local)

DCL(Device Clear)

SDC (Selective Device Clear)
GET (Group Execute Trigger)
Serial Polling (SPE,

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

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

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

.:

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

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

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

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

SPD)

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

DEVICE-DEPENDENT COMMAND PROGRAMMING ........................................

Execute (X). ..............................................................................

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

Channels A, d Coupling (AC, BC) .........................................................

Channels A, B Attenuator (AA, BA) .......................................................

Channels A, B Filter (AF, BF)
Channels A, B Slope (AS, BS).
Channels A, B Trigger Level (AL,

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

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

BL)

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

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

Gate Time(G) ...........................................................................

Delay Time(W) ..........................................................................

Delay(I) .................................................................................

Displayed Digits(N)

Triggering (T)

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

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

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

SRQ Mode (M) and Serial Poll Status Byte Format
Displayed Modes (D)
Self-Test

(J) ...............................................................................

READING FROM THE MODEL 775

Data Control Commands (B)
Status Word

Terminator (Y)
Prefix(P)

(U)

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

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

Dump Mode (53 Rate Mode)

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

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

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

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

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

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

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

3-4
3-5
3-5

3-5
3-6

3-6
3-6
3-6
3-6 1~

3-8
3-10

3-10. ...

3-10
3-11

3-L?
3-13
3-13
3-13

3-14

3-15

,3-15

3-15
3-16
3-16
3-19
3-19

3-19’ ’
3-20
3-20
3-20
3-20
3-21
3-22
3-22
3-23 I
3-23
3-23

3-23
3-24
3-26
3-27
3-27
3-28
3-29
3-30
3-31
3-31

TABLEOFCONTENTS

.

a 4.5.7

. +,4.5.8

3.12

3.x2.1

FRONT PANEL PROGRAhJ.MING

IDDCError .........................................................................................

3.12.2 IDDCO Error

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

...................................................................... 3-34

SECTION G-PERFORMANCE VERIFICATION

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

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

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

...

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

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

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

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

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

ii

413

‘~ 4.4

4.5

4.5.1

4.52

‘4.5.3

.,- 4.5.4

4.5.5

4.5.6

4.5.9

INTRODUCTION
ENVIRONMENTAL CONDITIONS
RECOMMENDED TEST EOUIFMENT
INITIAL CONDITIONS ­VERIFICATION PROCEDURES

Channels A, B and C Inputs Sensitivity.

Period Measurement Accuracy Check ...............................................

Period Averaged Measurement Accuracy Check
Tie Interval A-B Measurement Operation Check.,

Pulse A Measurement Operation Check.. ...........................................

Delay Operation Check
External Gate Operation Check
Arming Operation Check
Model7752TCXO Accuracy Check

SECTION 5-THEORY OF OPERATION

5.1

5.2

5.3

5.3.1

5.3.2

5.3.3

5.3.4

5.3.5

5.3.6

5.3.7

* 5.4

5.4.1

5.4.2

5.4.3

54.4

5.4.5

INTRODUCTION
OVERALL FUNCTIONAL DESCRIPTION
ANALOG CIRCIJITP.Y.

Input Circuits A and B ....................................................................

Input C~cuitC

1OMHz Standard Reference Oscillator
1OMHz ICXO Reference Oscillator
100MHzMultiplier

Measurement Section ......................................................................

Power Supply .............................................................................

DIGITAL CIRCUITRY

Microcomputer Block Diagram

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

Address Decoding
Keyboard/Display Interface
IEEE Interface

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

....................................................................... 5-3

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

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

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

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

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

........................................................................ 5-13

................................................................ 5-14

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

3-34
3-34

4-l
4-l

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

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

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

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

5-l

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

5-l

5-3
5-3

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

5-3
5-3

5-3
5-4

5-4

5-D
5-13

5-13

5-14

SECTION 6-MAINTENANCE

6.1

6.2
243

6.5

6.6

6.7

6.7.1

6.7.2

6.7.3

6.7.4

6.7.5

INTRODUCTION
LINE VOLIAGE SELECTION
FUSE REPLACEMENT
USING AN EXTERNAL TIME BASE,,
MODEL 7751 CHANNEL C OPTION INSTALLATION
MODEL 7752 TCXO OPTION INSTALLATION
CALIBRATION

Environmental Conditions.
Warm-Up Period
Recommended Test Equipment

Calibration Procedure

Multiplier Adjustment

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

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

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

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

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

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

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

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

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

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

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

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

6-l
6-l
6-l

6-2
6-3
6-4

6-5
6-5
6-5
6-5
6-5

6-7

iii

TABLE OF CONTENTS

6.7.6

6.7.7

6.7.8

6.7.9

6.7.10

6.8

6.9

6.10

6.10.1

6.10.2

6.10.3

6.10.4

6.10.5

6.10.6

6.10.7

6.10.8

6.10.9

Trigger Level Adjustment

Channels A and B Sensitivity Adjustment
Inputs A and B Attenuator Compensation
Tune Base Adjustment (Standard 5 PPM Tune Base)

Time Base Adjustment (Optional 1 PPM Tie Base)
SPECIAL HANDLING OF SEATIC SENSITIVE DEVICES

DISASSEMBLY INSTRUCI’IONS. .............................................................

TROUBLESHOOnNG ......................................................................

Recommended Test Equipment. ............................................................

Power-Up Self Diagnostics .................................................................

Power Supply Checks

Reference Oscillator and Clock Checks

Digital Circuitry and Display Checks

Signal Conditioning and Input Circuit Checks.

Multiplier Circuit Checks ..................................................................

Trigger Level Checks ......................................................................

Measurement Section Checks.. ............................................................

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

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

SECTION 7-REPLACEABLE PARTS

Zl

7.2

7.3

7.4

7.5

INTRODUCTION ............................................................................

PARTS LIST..

ORDERING INFORMATION .................................................................

FACTORY SERVICE
SCHEMATIC DIAGRAM AND COMPONENT LOCATION DRAWINGS

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

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

6-7

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

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

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

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

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

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

....................................................... 6-11

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

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

6-7

6-7

6-7

6-7

6-8

6-8
6-10
6-10
6-10
6-10
6-11

6-11
6-11
6-11
6-11

7-1
7-l
7-l
7-1

7-l
A
I

APPENDIX..
INDEX

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

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

A-l

I-l

iV

LIST OF ILLUSTRATIONS

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

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

3-9

3-10

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

6-l
6-2
6-3
6-4
6-5

Model775

Model775RearPanel ........................................................................

FallTime Measurement
Using Delay to Measure Contact Dwell Time
High Frequency Multiplexed Measurements

IEEE Bus Configuration
IEEE Handshake Sequence
Command Codes

System Types ............................................ 3-8

IEEE-468 Connector ......................................

IEEE-488 Connections., ...................................

Rear Panel of Model 775 Showing IEEE connector

Contact Assignments ..................................... 3-9

Typical IEEE-488 Bus Driver (One of 16)

IEEE-488 Display Error Messages ..........................

Model775 Simplified BlockDiagram
Frequency A Measurement Block Diagram.
Frequency B Measurement Block Diagram
Frequency C Measurement Block Diagram
Period A Measurement Block Diagram
Time Interval A-B Measurement Block Diagram
Pulse Width Measurement Block Diagram.
Microcomputer Block Diagram

Model 775 Standard 5ppm Timebase
Model 7751 Installation
Model 7752 Installation
Model 775 Calibration Adjustments

Model 775 Exploded View ................................

Front Panel

....................................................................... 2-2

2-3

..................................................................... 2-14

.................................................. Z-15

................................................... 2-15

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

................................ 3-3

........................................ 3-7

3-8

................... 3-10

.......................................................... 5-2

.................................................... 5-6

..................................................... 5-7

..................................................... 5-8

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

.................................................... 5-11

............................................................... 5-12

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

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

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

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

..,...

...........

.............................................. 5-10

.,..,.

.,....

3-9
3-9

3-35

5-9

6-2
b-3
b-4
6-6
6-9

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

7-5

7-b
7-7
7-8
7-9
7-10

Mother Board, Component Location Drawing
Mother Board, Schematic Diagram
Display Board, Component Location Drawing
Display Board, Schematic Diagram
Model 7751, Component Location Drawing

Model 7751, Schematic Diagram ....................................................

Model 7752, Component Location Drawing
Model 7752, Schematic Diagram
5 ppm Oscillator, Component Location Drawing.
5 ppm Oscillator, Schematic Location Diagram

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

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

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

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

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

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

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

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

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

7-11
7-13

7-26

7-27
7-29
7-30

7-31
7-32
7-33
7-34

LIST OF TABLES

2-l
2-2

3-l
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
3-11
3-12
3-D
3-14
3-15
3-16
3-17
3-18
3-19

3-20
3-21

4-l

Gate/Delay Determination.
Alarm Condition

IEEE-488BusCommand Summary
Hexadecimal and Decimal Command Codes

Typical Addressed Command Sequence

Typical Device-Dependent Command Sequence
IEEE Contact Designations
HP-85 IEEE-488 BASIC Statements
Model 775 Interface Function Codes,,

IEEE Command Groups .....................................................................

General Bus Commands
Default Conditions (Status Upon Power Up or After SDC or
Device-Dependent Command Summary

Rate Commands ............................................................................

Gate/Delay Time Predetermined Value.,
SRQ

Mask Commands

SRQ Mask Legal Commands..
Status Byte Interpretation
Data

String Format

Prefixes.

Status Word Format

DumpMode Specifications........................................................:

Dump Ouput Mode Result Calculation
Recommended Test Equipment for Performance Verification

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

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

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

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

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

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

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

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

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

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

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

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

DCL)

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

...................................................... 3-23

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

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

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

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

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

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

,
.

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

, ...................................

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

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

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

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

........ 3-13

3-24
3-25
3-26
3-28

..........

3-34

2-8

Z-13

3-4
3-h

3-b

3-6
3-9

3-11
3-12
3-13

3-15
3-17

3-21

3-2’)
3-30
3-33

5-l
6-l

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

6.11
6-12

7-l
7-2
7-3

Model775 Memory Mapping ................................................................

Line Fuse Selection
Recommended Test Equipment for Calibration

Static Sensitive Device
Recommended Minimum Test Equipment for Troubleshooting

Power Supply Checks

Reference Oscillator and Clock Checks

Digital Circuitry and Display Checks

Signal Conditioning Checks

Input Circuit Checks

Multiplier Circuit Checks
Trigger Level Circuit Checks..
Measuring Section Circuit Checks

Mother Board, Parts List

Display Board, Parts List

Model 775 Mechanical Parts List

........................................................................... b-l

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

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......

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................................................. 6-14

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.

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.................................. 6-K)

........................................ b-12

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5-13

6-5

6-8
b-11
6-12

b-13
6-U
6-13
b-14

7-2
7-25
7-35

vi

GLOSSARY OF TERMS

Time Base Uror4ime base error is the maximum frac-

tional frequency change in the time base frequency due

to all errors (e.g. aging, temperature, line voltage).

ligger Ermr-

q ei2 + en2

Input Slew Rate at Trigger Point

Where:

ei is the RMS noise voltage of the counter’s input channel

(25OhV typical).
en is the RMS noise of the input signal for lZ0MHz

bandwidth.

LSD-Unit value ot%eleast significant digit. Calculations

should ba rounded as follows: 1 to 1.3Hz becomes IHz,
l.hwec to liinsec becomes IOnsec, etc.

lklgger Timing Error-

35mV 35mV

+

Input Slew Rate at Start Input Slew Rate at Stop

Trigger Point Trigger Point

External Arming (Wgger) Delay-External arming delay

is the time from the positive going slope of the arming
signal to the internal gate open signal.

External Gate Delay-External gate delay is the time from

the positive going slope of the gating signal to the inter­nal gate open signal.

SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

The Keithley Model 775 Programmable CouirterlTimer is

a nine digit, microcomputer based, fully programmable,
universal counter/timer. The Model 775 measures with

high resolution the following parameters:

l

Frequency A

l

Frequency B

l

Frequency C

l

Period

. Period Averaged

l

Time Intervals A - B

l

Pulse Width (positive or negative) A

The Model 775 has an 14mm (0.56 in.) LED display. The
display consists of 9 digits with an additional digit for ex­ponent. The built-in interface makes the instrument fully
programmable over the IEEE-488 bus.

The Model 775 contains a programmable trigger level that

allows additional flexibility in measurements over the bus
(e.g. measuring rise and fall time with trigger points other
than 10% and 90%). Gate time is programmed in 46 steps
from 100psec to 1Osec or external from the front panel or
over the bus.

Trigger Delay Channel B-This feature is important for
some channel A - B time measurements.

True DC Coupling-Allows the Model 775 to do channel
A - B time measurements.

Reciprocal Technique-This counting method provides ad­vantages over all traditional counters from DC up to the
clock frequency (100MHz). The constant relative resolu­tion (8 digits/second independent of input frequency)
makes it even more useful for low frequency applications.

1.3 WARRANTY INFORMATION

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

1.4 MANUAL ADDENDA

1.2 MODEL 775 FEATURES

Dual Channel Capability-Dual channel capability with
two similar channels up to ‘IZOMHz.

Full Programmability-Full programmability of all func­tions and modes including different SRQ masks and chan­nel selection.

High Frequency Option-H&option adds a third measure­ment channel for frequencies up to 1GHz.

High Resolution-A 1OOMHz clock rate, along with the
latest technique in frequency counting (reciprocal techni­que), provides the high resolution of 8 digits/second or VIZ
out of a 1OOMHz input signal.

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

1.5 SAFETY SYMBOLS AND TERMS

The following safety symbols and terms are used in this
manual or found on the Model 775.

Then
should refer to the operating instructions in this manual.

The WARNING used in this manual explains dangers that
could result in personal injury or death.

symbol on the instrument denotes that the user

l-l

The CAUTION used in this manual explains hazards that
could damage the instrument.

1.6 INSPECTION

The Model 775 was inspected both mechanically and elec­trically before shipment. After unpacking all the items from

the shipping carton, check for any obvious signs of
physical damage that may have occurred during transit.
Report any damage to the shipping agent. Retain and use

the original packing materials in case reshipment is

necessary. The following items are shipped with every

Model 775.

Model 775 Programmable Counter/Timer

Model 775 Instruction Manual

Additional accessories as ordered.

If an additional Instruction Manual is required, order the

manual package (Keithley part number 775-901-00). The

manual package includes an instruction manual and any

applicable addenda.

1.7 USING THE MODEL 775 MANUAL

l

Section 1 contains general information about the
instrument.

l

Section 2 contains detailed operating information on us­ing the front panel controls and rear panel terminals.

l

Section 3 contains information necessary to operate the
Model 775 over the IEEE-488 bus.

l

Section 4 contains performance verification procedures
for the instrument. This information is helpful if you
wish to verify that the instrument is operating in com­pliance with stated specifications.

l

Section 5 contains a description of operating theory.

l

Section 6 contains information for servicing the instru­ment. This section includes information on line voltage
selection, fuse replacement, adjustments and
troubleshooting.

l

Section 7 contains replacement parts information.

Model 1019s Slide Rack Mount-The Model 10195 is a
sliding rack mount kit that allows the Model 775 to be rack
mounted with the added feature of sliding the instrument
forward for easy access to the rear panel and top cover.

Model 7007 IEEE-488 Shielded Cables-The Model 7007
connects the Model 775 to the IEEE-488 bus using shield­ed cables to reduce electromagnetic interference (EMI). The
Model 7007-1 is one meter in length and has an EM1 shield­ed IEEE-488 connector at each end. The Model 7007-2 is
identical to the Model 7007-1, but is two meters in length.

Model 7008 IEEE-486 Cables-The Model 7008 connects the
Model 775 to the IEEE-488 bus. The Model 7008-3 is 0.9m

(3 ft.) in length and has a standard IEEE-488 connector at
each end. The Model 7008-6 cable is identical to the Model
7008-3, but is 1.8m (6 ft.) in length.

Model 7051 BNC to BNC Cable--The Model 7051 is 1.5m
(5 ft.) in length and is terminated on each end with a BNC

Ph%
Model 7751 1GHz Channel C Option-The Model 7751 is

a factory-installed option which provides a third channel
(C) for measuring frequencies between 50MHz and IGHz.

Model 7752 TCXO-High Stability Crystal Oscillator
Option-The Model 7752 is a factory-installed TCXO-high

stability crystal oscillator that offers improvement over the
standard time base, relative to aging and temperature.

Model 7754-3 BNC to Alligator Cable-The Model 7754-3
is 0.9m (3 ft.) in length and is terminated on one end with
a BNC plug and on the other with two alligator clips.

Model 7755 5012 Feedthrough Termination-Ihe Model 7755
is a BNC tb BNC adapter for terminating RG 58 cable in

its characteristic impedance. VSWR <l.l, DC -250MHz.

SNC

PLUG

BNC

JACK

1.8 ACCESSORIES

The following optional accessories are available to enhance
the Model 775 capabilities.

Model 1019A Fixed Rack Mount-The Model 1019A is a sta­tionary rack mount kit that allows the Model 775 to be
mounted in a standard 19 inch rack.

l-2

SECTION 2

BASIC COUNTER/TIMER OPERATION

2.1 INTRODUCTION

Model 775 operation is divided into the two general
categories: basic bench operation, and IEEE-488 operation.
Basic bench operation which is covered in this section, con­sists of using the Model 775 to perform basic frequency
and time measurements. IEEE-488 programming can also
be used. These aspects are covered in detail in Sections
3 and 4. A layout of the front and rear panels of the Model
775 are shown in Figures 2-l and 2-2 respectively, includ-

ed is a brief description of each control, terminal and
indicator.

NOTE
Any front panel button push or IEEE device­dependent command (see Section 3) will cause the
measurement to restart, which will affect, for ex­ample, a measurement of the time from channels
A to B.

2-1

OPERATION

q

POWER ON/OFF-Turns the unit on or off.

q

FUNCIXON GROUP-

l

FREQ button toggles measurement between frequency
at channel A and frequency at channel 8.

l

PERIOD button toggles measurement b&./em the
period A and period average A.

l

TIME button toggles measurement between the time
interval A-B and pulse width of A.

l

MODE button places instrument in either the hold,
delay, both hold and delay, or normal mode.

El CHAN C-Measures frequencies from 50MHz to 1GHz

through channel C.

El

INPUT SEITING GROUP-

l

DC/AC button toggles instrument between AC and DC
coupling of the input signal.

* SLOPE button toggles instrument between the positive

or negative edge trigger.

l

A’lTEN button tot&sinstmment between the xl and
x10 input attenuZon.

l

FUR button toggles filter between on and off.

* LEVEL buttons select the threshold point on a signal

that the instrument will trigger.

El

DISPLAY MODIFY GROIJP­. GATE/DELAY button modifies display horn normal fre-

quency (or time reading) to gate time or delay time.

l

TRIGGER LEVEL button modifies the display to show
trigger level of both channels A and B.

El GATE/DELAY TIME CROUP-

. GATE/DELAY TIME buttons control: time gate is

open, delay of gate closure and number of digits
displayed.

l

These buttons increment or decrement the displayed
value by one step.

El

LOCAL-Enables front panel operation.

q

RESET-Resets display to initiate new measurement cy.

cle during normal or hold mode operation.

El TERMINALS-

l

CHAN A used when making frequency and time
measurements.

* WAN B used when making frequency and time A-B

measurmlents.

. CHAN C used when making high frequency measure-

ments up to 1GHz with a 500 input impedance (7751
option). The shell is connected to chassis ground as
indicated by the I symbol.

El DISPW AND INDICATORS-

l

Display consists of a nine digit mantissa and a single
digit exponent.

l

Ran

e indicator consist of Hz, SEC, V. Hz is on dur-

ing

qwncy measurement. SEC is on during time

te

and ,period measurements. V is on when TRIGGER
LEVEL button is pressed.

l

GATE indicator blinks at a rate proportional to gate
time.

l

IEEE status indicators select either remote. talk or listen
when programming over IEEE-488 bus.

2-2

Figure 2-1. Model 775 Front #Panel

OPERATION

CONNECrORS AND TRRMINALS-

El

l

AC receptacle connects to a three wire line cord
which provides connection to the line voltage.

l

IEEE-483 connector is used to connect the instrument
to the IEEE-488 bus. IEEE interface functions are
marked above the connector.

l

TRIGGER LEVEL OLPTPLJT connections are used to
connect the DC voltage level from the trigger circuits

to an external Dh4M or osciIloscope. DC output range
is marked above the connector.

l

CLOCK connactor is used to output the internal clock
as a reference to another instrument or to use an ax­ternal clock as the Model 775’s time base.

. EXT ARMING & GATE DELAY connector is used to

receive one of three signals: arming pulse, external
gate signal or external delay pulse.

Figure 2-2. Model 775 Rear Panel

LINE VOLTAGE SELEOR switch selects the line

El

voltage that the unit will operate on.
IEEE-488 address switches set the primary address for

El

IEEE-488 bus operation.
LINE FUSE provides protection on the AC power line

El

input.

2-3

OPERATION

2.2 FRONT PANEL FAMIC1ARIZATION

The front panel layout of the Model 775 is shown in Figure
2-1. The front panel is generally divided into three sections:
controls, terminals, and display and indicators. The follow­ing paragraphs describe the purpose of each of these items
in detail.

2.2.1~ Controls

All front panel controls except POWER are momentary
contact switches. Many controls include an annunciator
light to indicate the selected configuration. The controls
are color coded into functional groups for easier operation.

Front panel controls may be divided into the following
functional groups: Function, Input Setting, Display Modify
and Gate/Delay Time.

POWER-The POWER switch controls the AC power to the
instrument. Depressing and releasing the switch once
turns the power on. Depressing and releasing the switch
a second time turns the power off.

Function GrouP4he four FUNCTlON buttons control the
type of measurement, Each button is used to select one
of two functions.

MODE-Press the MODE button once to place the lnstru­ment in the hold mode. Press the RESET button to clear
the display and take a reading. The reading will be held
on the display until the RESET button is pressed again.
Pressing the MODE butt.on a second time, places the
Model 775 in the delay mode of operation; the instrument
holds off closure of the gate for the selected delay time.
Pressing the MODE button a third time places the instru­ment in both the hold and delay modes. Pressing of the
MODE button a fourth time turns the indicators off: and
places the instrument in the normal mode of operation.

NOTE

The delay ,mode is disabled in the frequency and

period averaging modes.

FREQ C--The: FREQ C button allows the Model 775 to
measure frequencies from 50MHz to lGHz on channel C.
Pressing the FREQ C button turns the C indicator on; ln­dicating the instrument is set to make high frequency
measurements on channel C. If the Model 7751 Channel
C option is not installed, a ‘no C OPY message will be
displayed for two seconds.

Input Setting Group-The six WAN A pushbuttons con­trol input attenuation, coupling, slope, trigger level and
high frequency noise suppression. The six CHAN B
pushbuttons are functionaly identical to the CHAN A
buttons.

FREQ-The FREQ button places the instrument in frequen­cy measurement mode. Pressing the FREQ button once
turns the A indicator on; indicating the instrument is set
for the frequency A mode. Pressing the button a second
time, turns the B indicator on; indicating the instrument
is set for the frequency B mode. Pressing of the FREQ but­ton toggles the measurement between the frequency at
channel A and frequency at channel B modes.

PERIOD-The PERIOD button places the instrument in
period measurement mode. Pressing the PERIOD button
once turns the A indicator on; indicating the instrument
is in the period A mode. Pressing the PERIOD button a
second time, turns the AVG A indicator on; indicating the
inetrument is in the period average A mode. Pressing of
the PERIOD button toggles the measurement between the
period A and period average A.

TIME-The TIME button sets the Model 775 up to measure

the time interval between channel A and 8. Pressing the

TIME button once turns the A-B indicator on; indicating

the instrument is in the time interval A-B mode. Press­ing the button a second time, turns the PLS A indicator
on; indicating the instrument is in the pulse A mode.
l’ressi,ig of the TIME button toggles the measurement bet­ween the time interval, A-B and pulse width of A.

DC/AC-The DC/AC button selects either the AC or DC
coupling mode. In default position, the instrument is in
the DC coupling mode. Pressing the DC/AC button turns
the AC indicator on; indicating the instrument is in the
AC coupling mode. Pressing of the DC/AC button toggles
the instrument between AC and DC coupling of the in­put signal.

SLOPE-The $LQPE button selects the slope that the
Model 775 will trigger on. In default position, the instru­ment triggers on a positive going edge. Pressing the SLQPE
button turns the ” 1
strument will trigger on a negative going edge. Pressing
of the SLOPE button toggles the instrument between the
positive or negative edge trigger.

ATTEN-The ATTEN button controls the attenuation of the
input signal. In default position, the signal will not be at­tenuated. Pressing the ATTEN button turns the x10 in­dicator on; indicating that the instrument will attenuate
the signal by Ill. Pressing of the ATTEN button toggles the
instrument between the xl and xl0 input attenuation. Note
that changing attenuation changes the trigger level. (e.g.
1V trigger on xl goes to lOV on x10).

” indicator on; indicating the in-

OPERATION

FLTR-The FLTR button limits high frequency noise to
about 1OOkHz through a low-pass filter installed at the in­put terminal. In default position, the low-pass filter is off.
Pressing the FLTR button turns the FLTR indicator on; in­dicating that the low-pass filter is on. Pressing of the FLTR
button toggles the filter between on and off.

LEVEL-The LEVEL buttons select the signal voltage level
that will trigger the instrument (e.g. start and/or stop the
measurement interval). Pressing the ‘I button decrements
the level by one step. Pressing the A button increments
the level by one step. Each step is 1OmV on the xl attenuator
setting or 1OOmV on the x10 attenuator setting. Holding the
LEVEL A or v button in for more than one second, causes
the trigger level to continuously move up or down respec­tively. Holding the LEVEL A and v buttons in at the same
time, causes the instrument to jump to the preset posi­tion O.OOV (or OO.OV).

Display Modify Group-The two pushbuttons in the
display modify group modify the display from normal fre­quency (or time reading) to another reading such as trig­ger level, gate time, delay time or displayed number of
digits.

GATE/DELAY-The GATE/DELAY pushbutton has two
functions: When instrument is in the frequency or period
averaged functions, this button modifies the display to
display the time that the gate remains open to complete
one cycle. When instrument is in the time interval, period
A or pulse A function, this button modifies the display
to show the time that the closure of the gate is delayed
after its opening. Press GATE/DELAY to exit.

TRIGGER LEVEL-The TRIGGER LEVEL button may be
used to modify the display to show the trigger level of both
channels A and B. Pressing !he TRIGGER LEVEL button
turns the indicator above the button on, indicating that
the instrument is in the trigger level display mode. The
display will contain two sets of readings (three digits for
each channel). The three digits to the left on the display
concern channel A, while the three digits to the right on
the display concern channel B. Use CHAN A or CHAN
B Level buttons to modify the values. Press TRIGGER

LEVEL to exit.

Display Function-The display function allows the user to
select the maximum number of most significant digits
which are to be displayed. In the normal operating mode,
the instrument will display a maximum of nine digits. The
minimum number of digits displayed is three. To access
the display function press simultaneously the
GATE/DELAY and TRIGGER LEVEL buttons. Select the
number of digits to be displayed by pressing the
GATE/DELAY TIME A or v button to increment or decre-

ment the display. To resume normal operation, simply
press any other button on the front panel. The instrument
will display its measurements with the preselected number
of digits.

GATE/DELAY TIME-The two GATE/DELAY TIME buttons
control: the time that the gate is open from 100~s~ to 1Osec
in 46 steps; the delay of the gate closure from 100psec to
1Osec in 46 increments; and the number of digits to be
displayed in increments of seven.

GATE/DELAY A, V-Each time the A button is pressed,
the gate or delay increments one step. Each time the v
button is pressed, the gate or delay decrements one step.
If A or v button is held in for more than one second, the
instrument will continuously increment or decrement. If
the A and v buttons are held in at the same time, the
instrument will jump to a preset position of laec delay time
or nine digits displayed numbers.

User Gate/Delay Function-Information on accessing this
function will be given later in this chapter.

LOCAL--Pressing the LOCAL button when the instru­ment is in remote operation (but not in remote (local)
lockout condition), will place the instrument in local opera­tion. Pressing this button when the instrument is already
in local operation will have no effect on the instrument.

RESET-Pressing the RESET button during normal opera­tion will reset the display and initiate a new measurement
cycle. When the instrument is in the hold mode of opera­tion, pressing the RESET button clears the display and

arms the instrument for the next measurement.

2.2.2 Terminals

The terminals are used to connect the Model 775 to the

signal to be measured.
Channel A-The CHAN A terminal is used when making

frequency and time measurements.
Channel B-The CHAN B terminal is used when making

frequency and time A-B measurements.
Channel C-The CHAN C terminal is used for high fre-

quency measurements up to 1GHz with a 5Ofl input im­pedance Although this terminal is always installed, the
internal circuitry needed to operate this function is optional
and may not be installed. BNC shell is connected to chassis
ground as indicated by the I symbol.

2-5

OPERATION

2.2.3 Display and indicators

The function of the display and indicators is described
below.

Display-The display consists of a nine digit mantissa and
a single digit exponent. The exponent uses a leading minus
to indicate negative values. The sign on the exponent
changes to + for zero or positive values. The dimension
is determined by the exponent and the Hz, SEC or V
indicdtors.

Units Indicators-The units are shown by three indicators.
The Hz indicator is on during frequency measurements
and the SEC indicator is on during time and period
measurements. When TRIGGER LEVEL button is pressed,
the V (volts) indicator turns on.

GATE Indicator-When the instrument takes a measure­ment, the GATE indicator blinks at a rate which is pro­portional to the gate time.

IEEE Status Indicators-The REMOTE, TALK and LISTEN
indicators are used when programming the instrument
over the IEEE-488 bus. Refer to Section 3 for complete IEEE
programming information. These status indicators are not
operational during front panel instrument operation.

2.2.4 Tilt Bail

IEEE-488 Connector--This connector is used to connect the
instrument to the IEEE-488 bus. IEEE interface functions
are marked above the connector.

TRIGGER LEVEL OUTPUT Connector-These two BNC
connectors are used to connect the DC voltage level from
the trigger circuits to an external Dh4M or oscilloscope. DC
output range is marked above the connectors.

CLOCK Connector-This BNC connector is used to out­put the internal clock as a reference to another instrument.
The same ihput may be connected to an external clock
reference. lb use an external clock reference, the internal
time base must be set for external operation. Refer to Sec­tion 6 for this procedure and proper signal levels to apply.

EXT ARMING & GATE/DELAY Connector-A BNdcon­nectar 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 than the in­ternal times are required or to take one reading with the
Model 775 in synchronized with other equipment.

2.3.2 LINE VOLTAGE SELECTOR Switch

The LINE VOLTAGE SELECTOR switch selects the line
voltage that, the Model 775 will operate on. For informa­tion on voltage selection refer to Section 6.

The tilt bail, which is located on the bottom cover of the
instrument, is useful for elevating the front of the instru­ment to a convenient viewing height. To extend the bail,
first rotate it 90” away from the bottom cover and push up
on the leg to lock it into pIdie. To retract the bail, pull the
legs away from the bottom cover and then rotate the bail
until it is flush with the bottom cover.

2.3 REAR PANEL FAMILIARIZATION

Figure 2-2 shows the rear panel lavout of the Model 775.

2.3.1 Connectors and Terminals

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.

2.3.3 IEEE-488 Address Switches

The IEEE-488 address switches are used to program the
primary.a@ress for IEEE-488 interface operation. The ad­dress may be set from 0 to 30.

2.3.4 Line Fuse

The LINE FUSE provides protection for the AC power line
input. For information on replacing this fuse, refer to Sec­tion 6.

2.4 POWER-UP PROCEDURE

The basic procedure of powering up the Model 775 is
described below.

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

2-6

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. If necessary, the power
line voltage may be changed by siidlng the
recessed LINE VOLTAGE SELECTOR switch to

the required voltage positlon. Refer to Section
6 for details

WARNING
The Model 775 is equipped with a 3.wire power
cord desianed to be used with arounded
outlets. When the proper connections are
made, instrument chassis Is connected to
power line ground. Failure to use a properly
grounded outlet may result in personal injury
or death because of electric shock.

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

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

8.8.8.8.8.8.8.8.8*8

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

Once the test is completed, the instrument will perform
ROM and RAM tests. If all these tests are passed, the
display will show the software revision level for about
one second similar to the example below:

SoFt A.1

Following the software revision level, the instrument
will display the default IEEE primary address which is
set by the IEEE address switch on the rear panel. For
example, with the rear panel switch set to address 23,
the display will show:

IE Adr 23

Following these display messages, the instrument will
go into the normal operating mode and is ready to take
readings, The instrument will be in the following
configuration:

OPERATION

l

Freq A

l

Gate/Delay Time = 1Sec

l

Trigger Levels = O.OOV

l

Filters: Off

l

Attenuators: Off

. DC/AC: DC

l

Slope: Positive

l

Mode: Normal

l

IEEE Status: Local

l

Displayed digits: 9

7. If any of the power tests fail, the instrument will lock
up and display an error message as follows:

FAtAL Err 1

It is recommended that the power-up procedure be
repeated several times to verify that a consistent error
occurs; if so, a problem exists in the instrument. See Sec­tion 6 for troubleshooting information,

2.5 DISPLAY MESSAGES

The Model 775 has two display messages associated with
basic front panel operation. One message indicates that
Model 7751 option is not installed, the other that gate time
or delay time are user selectable. Note that the instrument
has a number of additional display messages associated
with IEEE-488 programming.

2.5.1 No Option Message

The Model 7751 option must be installed in the instrument
before it can measure frequencies through the channel C
input terminal. If the FREQ C button is depressed and the
Model 7751 option is not installed, the following message
will be displayed:

no c oPt

NOTE
There are no additional software modifications re­quired after the Model 7751 option is installed.
After the Model 7751 option is installed, the no
option message will no longer be displayed.

2-7

OPERATION

2.6 CONTROL SELECTION

Selecting the various front panel operating modes is simply
a matter of depressing, once or twice, the appropriate but­ton as described in the following paragraphs.

2.6.1 Function

The Model 775 must be set up for the proper measuring

function with one of the four function buttons.

1. To measure frequency through the channel A input ter-

minal, depress the FREQ button.

2. To measure frequency through the channel B input ter-

minal, depress the FREQ button a second time.

3. To measure the period of a signal through the channel

A input terminal, depress the PERIOD button.

4. To measure the period averaged of a signal through the

channel A input terminal, depress the PERIOD button
a second time.

5. To measure time intervals from events in channel .4 to

events in channel B, depress the TIME button.

6. To measure the pulse width of a pulse at channel A in-

put terminal, depress the TIME button a second time.
Use the slope button(s) to select the desired portion of
the input signal.

7. To measure frequency through the channel C input ter-

minal, depress the FREQ C button.

2.6.2 Selecting Gate Time

The Model 775 may be operak:d in the present gate time
of one second or in one of 46 gate times which are factory
selected. When selecting the gate time, the instrument will
move up or down one gate time each time the A or V

button is pressed. The present gate time may be noted on
the display by pressing the GATE/DELAY button.

Select the gate: time as follows:

1. Press the GATE/DELAY button. The GATE/DELAY light
will turn on and the instrument will display the follow­ing message:

GAtE DDD*D SEC

2. To change the gate time press the GATE/DELAY TIME

A or V button. Pressing the A button will increase the

gate time. Conversely, pressing the V button will
decrease the gate time. Holding in the A or V button
for more than one second, causes the instrument to in­crement or decrement continuously.

3. Pressing the A and V buttons simultaneously will
change the gate time to a preset value of lsec.

4. To resume normal display operation, ~depress the

GATE/DELAY button. The GATE/DELAY light will turn

off and instrument will be ready to perform

measurements with the newly selected gate time. Table
2-1 lists the gate/delay times which are available.

It is also possible to change the gate time without observ­ing the actual gate time on the display. To do so, simply
press the GATE/DELAY TIME A or V button. Each time
the A button #is pressed, the instrument will increment

one gate time. Each time the V button is pressed, the in-

strument will decrement one gate time. Holding in the A
or V button for more than one second, causes the instru­ment to increment (or decrement) after each measuring
cycle.

2.0

Table 2-1. Gate/Delay Determination

OPERATION

NOTE

To prevent operator error, there is an internal

alarm that beeps whenever a limit is reached,
(e.g. 1OOjwsc low limit or 1Osec high limit). With
the GATE/DELAY light on, the alarm will sound
when the users gate is displayed and the A but­ton is pressed. Refer to Table 2-2 alarm conditions.

2.6.3 User Gate Function

The user gate function is useful when a gate time other
than the predetermined gate times listed in Table 2-l is re­quired. The limits which must be observed are the

minimum limit of lO@sec and the maximum limit of 10sec.
The user gate function is accessible in the FREQ A, B and
C and Period Averaged functions. To operate the instru­ment in the user gate mode proceed as follows:

1. Press the GATE/DELAY button and observe that the light
turns on and the instrument displays the’ following
message:

GAtE DDD+D SEC

2.6.4 Using Delay

The Model 775 has a delay function which disables the

closure of the opened gate for the predetermined periods
listed in Table 2-1. This function is very useful in burst
measurements, relay open/close time measurements where

bounce time should be eliminated or in measurements

done on a train of pulses.

NOTE

The delay mode is accessible only when PERIOD

A, TIME A-B or PLS A functions are on. The
selection of any other function, when the DELAY
light is on, will cause the instrument to exit from
delay mode

The delay time may be selected as follows:

1.

Press

the GATE/DELAY button. The GATE/DELAY light
will turn on and the instrument will display the follow­ing message:

dELAY DDDiD SEC

This display shows the actual gate time that the instru-

ment is set to operate. DDDiD SEC may be any time
from lOOE-6 to 10EcO.

2. Press and hold in the GATE/DELAY TIME A button and
observe that the display increments. After the 10s~ gate
time the instrument will enter the user gate mode and
the instrument will display the following:

USEr GATE SEC

Pressing the A button after the gate is displayed will
sound an alarm.

3. Press the GATE/DELAY button. The light will turn off
and the instrument will be ready for measurements with
an external gate time.

4. Apply a ‘ITL pulse to the rear panel EXT ARMING &
GATE/DELAY BNC terminal. The high level of the TTL
pulse width determines the length of the gate time.

NOTE
The user gate function may be accessed only
when the GATE/DELAY light is on. To exit the
user gate function press the GATE/DELAY TIME

V button, or both the A and V buttons to preset

the gate tiine to kc.

2. To change the delay time, press the GATE/DELAY TIME
A or V button. When the A or V button is depressed
for more than one second, the instrument will increment

or decrement continuously.

3. Pressing the A and y buttons simultaneously will

change the delay time to a preset value of lsec.

4.To resume normal display operation, press the
GATE/DELAY button. The GATE/DELAY light will turn
off and instrument will be ready to perform measure­ment with the newly selected delay time. Table 2-1 lists
the gate/delay times which are available as preselected
values.

It is also possible to change the delay time without obser-

ving the actual delay time on the display. To do so, simpl;,

press the GATE/DELAY TIME A or V button. Exh timk
the A button is pressed, the instrument will increment

one delay time. Each time the V button is pressed, the

instrument will decrement one delay time. When A or V

button is held in for more than one second, the instru-

ment will increment (or decrement) after each measuring

cycle.

2-9

OPERATION

NOTE
To prevent operator error, there is an internal
alarm that beeus whenever a limit is reached.
(e.g. 100ssec 10; limit or 1Osec high limit). When
the GATE/DELAY light is on, the alarm will
sound when the user’s delay is displayed and the

A button is pressed. Refer to Table 2-2.

2.6.5 User Delay Function

The user delay function is useful when a delay time other

than the predetermined delay times listed in Table 2-l is
required. The limits which must be observed are the
minimum limit of 100ssec and the maximum limit of

10,OOOsec. The user delay function is accessible in the
PERIOD A, TIME A-B or PLS A functions. To operate
the instrument in the user delay mode proceed as follows:

1. Press the GATE/DELAY button and observe that the light
turns on and the instrument displays the following
message:

dELAY DDD*D SEC

This display is the actual delay time that the instrument

is set to operate. DDDiD SEC may be any time from
lOOE-6 to lOE+O.

2. Press and hold in the GATE/DELAY TIME UP button
and observe that the display increments. After the 1Osec
delay time the instrument will enter the user delay mode
and the instrument will display the following:

NOTE
The user,delay function may be accessed only
when the GATE/DELAY light is on. To exit the user
delay mode simply depress the GATE/DELAY
TIME v button, or both the A and v buttons to
preset the delay time to lsec.

2.6.6 Selecting Measurement Rate

There are four measurement rates which are available on

the Model 775. Only two measurement rates are accessi­ble from the front panel: normal rate and single cycle
(Hold). The other measurement rates are accessible only
via the rear panel IEEE-488 bus and will be discussed in
further detail in Section 3. To select the measurement rate
proceed as follows:

1. Refer to the front panel MODE indicator: The HOLD
light determines the rate of measurement. When the in­dicator is off, the instrument is in the normal measure­ment rate.

2. Press the HOLD button. The HOLD light will turn on
and the instrument will go into the one-shot measure­ment cycle.

3. Press the RESET button. This action will clear the
display andthe Model 775 will be ready to take and pro­cess the next signal from the input terminal (see
paragraph 2.7 for arming).

2.6.7 Selecting the Number of Displayed Digits

USEr dLAY SEC

Pressing the A button after the user delay time is
displayed will sound an alarm.

3. Press the GATE/DELAY button and observe that the light
turns off.

4. Press the MODE button twice. The first time the MODE
button is pressed, the HOLD light will turn on. The se­cond time the button is pressed, the DELAY light will
turn on and the instrument will be ready for
measurements with an external delay.

5. Apply a TTL high level pulse to the rear panel EXT
ARMING & GATE/DELAY terminal. Delay would then

be enabled as long as this input is kept at a TTL high

level. The first negative transition to TTL low at this in­put will disable the delay. The delay would then be
disabled as long as this input is kept at a TTL low level.

2-10

A major advantage of the Model 775 is its capability to
display a fixed number of digits regardless of the frequen­cy of the sign@ For example, with a one second gate time,
the Model 775lis capable of displaying a minimum of eight
digits. This however, may turn out to a disadvantage when
measuring a frequency 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 775 is designed in such a way
that it truncates the unstable least significant digits while
still preserving the full performance of the Model 775. To
select the number of displayed digits proceed as follows:

1. Press the GATE/DELAY and TRIGGER LEVEL buttons
simultaneously. The respective indicators will light and

the following message will appear on the display.

D dIGIt

OPERATION

Where: D is any number from 3 to 9. The factory selected

default number for D is nine. This means that the max­imum number of digits that the Model 775 is capable
of displaying 9.

2.To change the number of displayed digits, press the
GATE/DELAY TIME A or v button until D is equal to

the required number of digits.

NOTE
Selecting five digits to be displayed, instead of
nine, will eliminate the four least significant digits
and will move the entire dis lay to the right by
four places. An example o P a normal display
reading, and the same display reading with five
digits of resolution is given as follows.

Display reading with nine digits:

1.13456789Hz

Display reading with selected five digits:

1.1345Hz

To change the input setting proceed as follows:

1. To change the slope that the instrument will trigger on,
press the SLOPE button. If the 1 indicator light is
off, the counter will trigger on the positive edge of the
input signal. If the \ indicator light is on, the counter
will trigger on the negative going edge.

2. To select the required coupling mode, press the AC/DC
button. The instrument is in the DC coupling mode
when the AC indicator light is off. When the AC in­diii;zr light is on, the instrument is in the AC coupling

3. When the signal exceeds the specified dynamic range
of the input, attenuation is required. To attenuate the
signal, press the ATTEN button. The input signal will
be attenuated by a factor of 10 when the light is on.
When the light is off, the input signal will not be

attenuated.

4. In low frequency measurements where the frequency
range is below lCOKI-Iz, the use of a filter is recommend­ed to attenuate high frequency signals which may in­terfere with the measurement. To apply a filter depress
FLIR button, the FLTR light will turn on.

2.6.9 Setting Trigger Levels

3. To return the Model 775 to the normal mode of opera­tion, simply press any button on the front panel, except

the LOCAL button.

NOTE
In certain circumstances, it is possible that the
Model 775 will display less than nine digits. This
may occur when the selected gate time is very
small. In this case, the instrument will override
the function of the selected number of digits and
will display only as many digits as it can. When
gate time is increased, the Model 775 will again
limit the number of displayed digits to the
selected value.

2.6.6 Input Condition Controls Setting

A proper setup of the input controls will ensure proper
operation of the instrument. There are six buttons which
control the input. These buttons are identical in both chan­nels A and 8.

Changing one of the input setting controls is simply a mat­ter of pressing the required button. There are four lights
which :re associated with each of the controls which will
turn on when a button is pressed.

There are two LEVEL buttons associated with both chan­nels A and 8. The LEVEL buttons set the signal 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.

1. Press the TRIGGER LEVEL button. The TRIGGER
LEVEL indicator will turn on and the display will rexi
as follows:

-D.DD -D.DD VOLT

The display segment ‘iD.DD” may have any value from

-2.55 to +2.55 if the “ATTEN” indicator is off. When the
ATTEN indicator is on, the value may range from -25.5
to +25.5. Also, note that the left three digits on the
display are associated with channel A and the three
digits on the right side of the display are associated with
channel B.

2-11

OPERATION

2. Simultaneously press the two LEVEL buttons and note
that the display section associated with channel A resets
to 0. The display wiIl appear as follows:

0.00 -D.DD VOLTS

3. To set a positive tri
Holding in the A or
cond, will cause the instrument to Increment or decre­ment continuously.

Pressing the LEVEL A or v button, when the
limits of +2.55 or -2.55 respectively have been
reached, will sound an alarm.

4. Press the TRIGGER LEVEL button. The indicator light
will turn off and the instrument will return to the
previous measurement state.

It is also possible to change the trigger level set­ting without observing the trigger level setting on
the display. To do so, proceed as follows:

er level press the A button.

9 button for more than a % se-

NOTE

NOTE

with infinite gate time, pulses are counted for as long as
they are present at the input terminal. This is called cum­mulative totalize mode. It is also possible to limit the
amount of time that the pulses are counted. This is done
by utilizing the total&e A by B mode, where a gating signal
on Channel B permits counting of channel A pulses

To operate the Model 77% in totalize A by 8, proceed as
follows:

1. Simultaneously press the FREQ and PERIOD buttons.
Note that, all function lights are turned off, indicating
that the instrument is set to operate in totaliie.

NOTE: Upon power up, the totalize function defaults
to totalire A by B.

2. Connect the signal to be counted to the Channel A in­put terminal.

3. Connect the gatin
minal. The GATE ight illuminates whenever t
at Channel B is above the selected trigger level.

NOTE: Press the RESET key to set counts back to zero.

4. Set Channels A and B to the required trigger level, mak­ing sure that the gating signal will cross the threshold

level.

signal to the Channel B in

F R

ut ter­e level

1. Select a function and gate time as discussed previously
in this section and apply the signal to be measured to

the appropriate input terminal.

2. To preset the trigger level, press both LEVEL A and v

buttons simultaneously. Observe the display, if the

GATE light flashes and the Model 775 dis
setting. If the GATE light does not flash or the reading

is noisy, press and hold in the LEVEL A button. The

instrument will increment until the bottom peak of the

signal is found. At this point the instrument will beep,
signalin
the GA 7%

Pressing and holding in the LEVEL A button after the

signal has been found will increment the instrument
once after every measurement cycle.

If the si nal cannot be found in the positive range of
OV to 2.

the A button is released. In this instance, continue to
search for the signal in the negative range of OV to -2S5V
using the T button.

to the user that the signal has been found, and

light will flash at a rate equal to the gate time.

V, the Model 775 will beep continuously until

.h

lays a steady

R result, there is no further need to change t

e trigger level

2.6.10 Selecting Totalize Operation

NOTE: Whenever the voltage level at the Channel B in­put terminal is above the Channel B programmed trig­ger level, the gate will open and the Model 775A will

accumulate the counted pulses at the Channel A input.
The gate may also be left open when Channel B is set
to a negative trigger level and no cable is connected to

its input.

To operate the Model 775A in the cumulative totalize mode;

proceed as follows:

1. Simultaneously press the FREQ and PERIOD buttons.
Note that, all function lights are turned off, indicating
that the instrument is set to operate in totalize.

2. Press the GATE/DELAY button. The GATE/DELAY light
turns on’ and the instrument displays the following
message:

tot A by B

The Model 775A is set to operate in totalize A by B.

3. To operate with infinite gate time, press the GATE/
DELAY A button once. The instrument displays the
following message:

tot InF

The totalize mode is used when counting the number of
pulses at the Channel A input terminal. Pulses may be
repetitive or erratic. When the Model 77% is set to operate

2-12

The Model 775 is set to operate in totaliie mode with

an in&rite gate time. Repeatedly pressing the button will
toggle the unit between the two gating options,

W’efiAlION

4. Press the GATE/DELAY button. The GAIEIDELAY indi­cator turns off and the GATE light turns on.

5. Connect the signal to be counted to the Channel A in­put terminal. The Model 775A will begin accumulating
counts.

2.7 ARMING

Arming allows a measurement to be triggered by the in­put signal. The Model 775 may be armed to take readings
in four ways:

1. Continuously armed in the normal mode.

2. With the front panel RESET button when the instrument
is in hold mode.

3. Through an arming pulse applied to the rear panel EXT
ARMING & GATE/DELAY input when the instrument
is in the hold mode.

4. With commands given over the IEEE-488 bus as des­cribed in Section 3. This section covers front panel and
external arming in detail.

2.7.1 Continuous Arming

When the instrument is not in the hold mode and there
is no signal present at the input terminals, the instrument
will stay in the idle state and the GATE 1iFht will not flash.
An input signal with the correct dynanuc range and cor­rect input control setting will initiate, a measurement cy­cle and the GATE light will flash wery time the internal

gate opens.

2.7.3 External Arming

External arming operates much like front panel arming ex­cept for the arming stimulus itself. In this case the arm­ing stimulus is applied to the rear panel EXT ARMING
& GATE/DELAY terminal (see Figure 2-2). The input arm­ing pulse must conform to TTL levels. To use external ar­ming, proceed as follows:

1. Place the instrument in the hold mode by pressing the
MODE button, (refer to parapaph 2.7.2). Note that the

GATE light will not flash, indlcatmg that the instrument
is in one-shot mode. The instrument will cease process­ing readings while it is waiting for the arming signal.

2. Connect the external arming source to the rear panel

EXT ARMING & GATE/DELAY connector. The first
positive going pulse at the input terminal will cause the
Model 775 to take and process the next available signal.
Note that after each positive going transition of the ar-

ming signal, the numeric display will be set to read zero
until the next data is processed and displayed.

3. To return the instrument to the continuous mode, press

and release the MODE button until the HOLD light
turns off.

2.7.4 Alarm Conditions

Table 2-2 lists the front panel conditions that will cause

the instrument to sound an audible alarm. Some of these
conditions are errors, while others provide information to
the user.

Table 2-2. Alarm Conditions

2.7.2 Front Panel Arming

Front panel arming is done with the RESET button. This

arming mode is very useful in burst measurements where
a signal is present on1
ming perform the

1. Enter the hold mode by pressing the MODE button. The
HOLD light will turn on and the GATE light will cease
flashing; indicating the instrument is in the one-shot ar­ming mode. The display will zero and no new readings
are processed until an arming stimulus is applied.

2. To trigger a single reading, press and release the RESET
button. The instrument will be ready to take and pro­cess the next reading.

3. To arm the instrument for a new measurement, press
the RESET button, the display will zero.

4. To remove the instrument from the one-shot arming
rnc !e, press the MODE button until the HOLD light
turns off.

temporarily. To use front panel ar-

Y

fol owmg steps.

Item

r

Description

1

Pressing two buttons other than those
specified as legal.

2

Pressing the GATE/DELAY TIME A or “V
button when high or low limits are
reached.

3

Pressing the LEVEL A or V button when
upper or lower limits are reached.

4

After selecting the number of digits to be
displayed, pressing the LEVEL A or V but­ton after the limits are reached.

2.8 APPLICATIONS

Applications for the Model 775 are many and varied and
will depend on the user’s needs. Figure 2-3 contains an
application concerning fall time m,easurements; while
Figure 2-4 contains an application usmg delay to measure
contact dwell time. For application information on high fre-

quency multiplexed measurements, refer to Figure 2.5.

2-13

OPERATION

1. Attach the input to channels A and B. (Use a BNC TEE connector.)

2. Display the trigger levels and adjust level A = 2.55V, level B = -2.55V.

3. Display frequency A and hold the level v button in until a gate occurs.

4. Display frequency B and hold the level A button in until a gate occurs,

5. Display trigger levels to realize the p-p voltage of the input signal. Assuming figure above, trigger A = .55V and trig
ger B = -.62V.

NOTE: While displaying frequency and holding a level button, the trigger level changes rapidly until a reading is
triggered; after which the level changes slowly (at one step per reading). This feature provides a means to detect the
peaks of an input sigal.

6. Set trigger A and trigger B levels to the 90% and 10% points (i.e. A = .4W and B = -.5V).

7. Set CHAN A and CHAN B to negative slope.
fi Display fall time by displaying time A-B.

NOTE: To verify the above procedure, measure the trigger level output voltage at the rear panel of the Model 775.

Y. To use this procedure over the bus, trigger levels must be sent by the controller, while monitoring the serial poll byte

for “reading done”. See Section 3 of this instruction manual.

Figure 2-3. Fall Time Measurement

214

OPERATION

(CONTACT BOUNCE TIME ltb,

1. Connect a signal to channel A input and select TIME PLS A.

2. Set the slope at channel A to trigger on the rising OI the falling edge, for high time or low time measurements.

3. Set the delay time to a value between the bounce time (tb) and the pulse width (tw) so that the bouncing is ignored.

4. The counter is now reading tw time. The delay in gate closing prevented the initial bounce time from prematurely
closing the gate.

Figure 2-4. Using Delay to Measure Contact Dwell Time

7063 500 RF SCANNER CARD

DC 120MHz

CHANNEL A OR 6

1. Use a 5061 feedthrough terminator (Model 7755) to balance line at inputs of channel A or B.

775

Figure 2-5. High Frequency Multlplexed Mesurements

215/z-16