Tektronix 775A Instruction Manual

Instruction Manual

Model 775A

Programmable Counter / Timer

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.

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

2-9

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

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

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

...

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

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

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

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

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

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

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

6-8

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

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

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

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

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

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

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

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

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

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

..........

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

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

......

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

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

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

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

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

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

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

5-13

6-5

6-8 b-11 6-12

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

7-2 7-25 7-35

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:

Frequency A

Frequency B

Frequency C

Period

. Period Averaged

Time Intervals A - B

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

Section 1 contains general information about the instrument.

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

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

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.

Section 5 contains a description of operating theory.

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

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

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

FUNCIXON GROUP-

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

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

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

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.

INPUT SEITING GROUP-

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.

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

FUR button toggles filter between on and off.

* LEVEL buttons select the threshold point on a signal

that the instrument will trigger.

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

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

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.

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

LOCAL-Enables front panel operation.

RESET-Resets display to initiate new measurement cy.

cle during normal or hold mode operation.

El TERMINALS-

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-

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

Ran

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

ing

qwncy measurement. SEC is on during time

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

GATE indicator blinks at a rate proportional to gate time.

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-

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

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

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.

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

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

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

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

Freq A

Gate/Delay Time = 1Sec

Trigger Levels = O.OOV

Filters: Off

Attenuators: Off

. DC/AC: DC

Slope: Positive

Mode: Normal

IEEE Status: Local

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:

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

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

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-

fol owmg steps.

Item

Description

Pressing two buttons other than those specified as legal.

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

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

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

SECTION 3

IEEE-488 OPERATION

3.1 INTRODUCTION

The IEEE-488 bus is an instrumentation data bus with stan-

dards adopted by the IEEE (Institute of Electrical and Electronic Engineers) in 1975 and given the IEEE-488 designation. The most recent revision of bus standards was made

in 1978; hence the complete description for current bus standards is the IEEE-488-1978 designation. The Model 775

conforms ~CI 1978 standards.

This section contains genera1 bus information as well as

detailed programming information and is divided as follows:

General introductory information pertaining to the IEEE-488 bus may be found primarily in paragraphs 3.2 through 3.6.

Information necessary to connect the Model 775 to the bus is contained in paragraph 3.7 and 3.8.

General bus command programming is covered in

3. paragraph 3.9.

Device-dependent command programming is described in detail in paragraph 3.10. The commands outlined in this section can be considered to be the most important since they control virtually all instrument functions.

Additional information pertaining to front panel error

5. messages and controller programs can be found in paragraphs 3.11 and 3.12.

3.2 BUS DESCRIPTION

bus has only eight data lines that are used for both data and most commands. Five bus management lines and three handshake lines round out the complement of signal lines. Since the bus is of parallel design, all devices connected to the bus have the same information available simultaneously. Exactly what is done with the information by each device depends on many factors, including device capabilities.

A typical bus configuration for controlled operation is shown in Figure 3-l. The typical system will have one controller and one or more instruments to which commands’ are given and, in most cases, from which data is received.

Generally, there are three categories that describe device

operation. These designations include: controller; talker;

listener.

The controller does what its name implies: it controls other

devices on the bus. A talker sends data, while a listener receives data. Depending on the instrument, a particular device may be a talker only, a listener only, or both a talker and listener.

Any given system can have only one controller (control may be passed to an appropriate device through a special command), but any number of talkers or listeners may be present up to the hardware constraints of the bus. Generally, the bus is limited to 15 devices, but this number may be reduced if higher than normal data transfer rates are required or if longer than normal cables are used.

The IEEE-488 bus as designed as a par?llel data transfer

medium to optimize data transfer without using an ex-

cessive number of bus lines. In keeping with this goal, the

Several devices may be commanded to listen ,lt NKP, but only one device may be a talker at any given time. Otherwise, communications would be scrambled.

3-1

IEEE-488 OPERATION

TO OTHER DEVICES

Once the device is addressed to talk or listen, appropriate bus transactions are set to take place. For example, if an instrument is addressed to talk, it will usually place its data on the bus one byte at a time. The listening device will then read tqs information, and the appropriate software can then be used to channel the information to the desired location.

3.3 IEEE-488 BUS LINES

DEVICE 3 )NLY ABLE r0 LISTEN IPRINTER,

, DATA BUS

DATA BYTE

TRANSFER

CONTROL

GENERAL

INTERFACE

MANAGEMENT

} D101...8 DATA 18 LINESI

v FD HANDSHAKE

BUS MANAGEMENT

The signal limes on the IEEE-488 bus are grouped into three general categories. The data lines handle bus information, while the handshake and bus management lines ensure that proper data transfer and bus operation takes place. Each of the bus lines is active low so that approximately zero volts is a logic one. The following paragraphs describe the purpose of these lines, which are shown in Figure 3-l.

3.3.1 Bus ,Management Lines

The bus management group is made, up of five signal lines

that help ensure an orderly transfer of ,data. These lines are used to, send the unihne commands described in paragraph 3.4.1.

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

cribed in paragraph 3.4. IFC (Interface Clear)-Setting the IFC line true (low) causes

the bus to go to a known state. REN (Remote Enable)-Setting the REN line low sends the

REN command. This sets up instruments on the bus for remote operation.

Figure 3-1. IEEE Bus Configuration

Before a device can talk or listen, it must be appropriately addressed. Devices are selected on the basis of their primary address; the addressed device is sent a talk or listen command derived from its primary address. Normally, each device on the bus has a unique primary address so that each may be addressed individually. The bus also has another addressing mode called secondary addressing, but not all devices use this addressing mode.

3-2

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

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

3.3.2 Handshake Lines

The bus uses three handshake lines that operate in an in-

terlocked sequence. This method ensures reliable data transfer regardless of the transfer rate. Generally, data

IEEE-488 OPERATION

transfer will occur at a rate determined by the slowest active device on the bus.

One of the handshake lines is controlled by the data source, while the remaining two lines are controlled by ac-

cepting devices. The three bus handshake lines are: DAV (Data Valid)-The source controls the state of the DAV

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

state of the NRFD line. NDAC (Not Data Accepted)-The acceptor also controls the

NDAC line.

The complete handshake sequence for one data byte is shown in Figure 3-2. Once data is on the bus, the source checks to see that NRFD is high, indicating that all devices on the bus are ready for data. At the same time NDAC should be low from the previous byte transfer. If these conditions are not met, the source must then wait until the

NRFD and NDAC lines have the correct status. If the source is a controller, NRFD and NDAC must remain stable for at least 1OOnsec after ATN is set low. Because of the possibility of bus hang up, some controllers have time-out routines to display error messages if the handshake sequence stops for any reason.

Once the NRFD and NDAC lines are properly set, the source sets the DAV line low, indicating that data on the bus is now valid. The NRFD line then goes low; the NDAC line goes high once all devices on the bus have accepted the data. Each device will release the NDAC line at its own rate, but the NDAC line will not go high until the slowest device has accepted the data byte.

After the NDAC line goes high, the source then sets the DAV line high to indicate that the data on the bus is no longer valid. At this point, the NDAC line returns to its low state. Finally, the NRFD line is released by each of the devices at their own rates, until the NRFD line finally goes high when the slowest device is ready, and the bus is set to repeat the sequence with the next data byte.

The sequence just described is used to transfer both data and multiline commands. The state of the ATN line determines whether the data bus contains data or commands as described in paragraph 3.4.

3.3.3 Data Lines

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

to be transmitted and received in a bit-parallel, byte-serial manner. These eight lines use the convention DIOl through DIOS instead of the more common DO through D7 binary terminology The data lines are bidirectional and, as with the remaining bus signal lines, low is true.

DA”

NRFD

VALID

SOURCE

ACCEPTOR

NDAC

DATA

TRANSFER

BEGINS ENDS

DATA

TRANSFER

ACCEPTOR

Fl;ure 3-2. IEEE Handshake Sequence

3.4 BUS COMMANDS

While the hardware aspect of the bus is essential, the in-

terface would be essentially worthless without appropriate commands to control communications between the various instruments on the bus. This paragraph briefly describes the purpose of the bus commands, which are grouped into

the following three general categories: Uniline commands-Sent by setting the associated bus line

low. Multiline commands-General bus commands which are

sent over the data lines with the ATN line low (true). Device-dependent commands-Special commands that

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

3-3

IEEE-488 OPERATION

Command Type

Uniline

Multiline

Universal

Addressed

Unaddress

Device-dependent**

Table 3-1. IEEE-488 Bus Command Summary

Command REN (Remote Enable) EOI

1FC (Interface Clear) ATN (Attention) SRQ (Service Request)

LLO (Local Lockout) DCL (Device Clear) SPE (Serial Poll Enable) SPD (Serial Poll Disable) SDC (Selective Device Clear) GTL (Go To Local)

GET (Group Execute Trigger)

UNL (Unlisten)

UNT (Untalk)

state of

TN Line” Comments

X X Sent by setting’EO1 low. X Clears Interface

Low Defines data bus contents.

X Controlled by external device.

Law Law Lmv Enables serial polling. Low Disables serial polling. Law

Low Low Low Law

High

-I-

Set up for remote operation.

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

Returns unit to default conditions.

Returns to local control.

Triggers device for reading.

Removes all listeners from bus. Removes all talkers from bus. Programs Model 775 for various modes.

Don’t Care

*x =

**See paragraph 3.10 for complete description

3.4.1 Uniline Commands

Uniline commands are sent by setting the associated bus line low. The ATN, IFC and REN commands are asserted only by the system controller. The SRQ command is sent by an external device. The EOI command may be sent by either the controller or an external device depending on

the direction of data :.ansfer. The following is a brief description of each command.

REN (Remote Enable)-When the controller sends the REN command, the instrument will be set up for remote operation. Generally, the REN command should be sent befom attempting to program instruments over the bus.

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

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

ATN (Attention)-The controller sends ATN while transmitting addresses or multiline commands. Device-

Dependent commands are sent with the ATN line high (false).

SRQ (Service Request)-The SRQ command is asserted by an external device when it requires service from the controller. If more than one device is present, a serial polling sequence, as described in paragraph 3.9.8, must be used

to determine which device has requested service.

3.4.2 Universal Commands

Universal commands are multiline commands that require no addressing AU instrumentation equipped to implement the command will do so simultaneously when the command is itransmitted over the bus. As with all multiline commands, the universal commands are sent over the data lines with ATN low.

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

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

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

in the serial polling sequence, which is used to determine

which instrument has requested service with the SRQ command.

3-4

IEEE-488 OPERATION

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

3.4.3 Addressed Commands

Addressed commands are multiline commands that must

be preceded by a listen command derived horn the device’s

primary address before the instrument will respond. On-

ly the addressed device will respond to each of these

commands:

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

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

GET (Group Execute Trigger)-The GET command is used to trigger devices to perform a specific action that depends on device configuration. Although GET is considered to be an addressed command, many devices res-

pond to GET without being addressed.

quency A mode. The IEEE-488 bus treats device-dependent commands as data in that ATN is high (false) when the commands are transmitted.

3.5 COMMAND CODES

Each multiline command is given a unique code that is transmitted over the data bus as 7-bit ASCII data. This section briefly explains the code groups which are summarized in Figure 3-3. Every command is sent with ATN low.

Addressed Command Group (ACG)-Addressed commands are listed in column O(B) in Figure 3-3. Column O(A) lists the corresponding ASCII codes.

Universal Commad Group (UCG)-Columns l(A) and l(B) list the universal commands and the corresponding ASCII codes.

Listen Address Group (LAG)-Columns 2(A) and 3(A) list the ASCII codes corresponding to the primary address listed in columns 2(B) and 3(B). For example, if the primary address of the,instrument is set to 16, the LAG byte will correspond to an ASCII zero.

Talk Address Group (TAG)-TAG primary address values and the corresponding ASCII characters are listed in col-

umns 4(A) through 5(B).

3.4.4 Unaddressed Commands

The two unaddressed commands are used by the con-

troller to remove all talkers and listeners from the bus simultaneously. ATN is lov. when these multiline commands are asserted.

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

UNT (Untalk)-The controller sends the UNT command

to clear the bus of any talkers.

3.4.5 Device-Dependent Commands

The meaning of the device-dependent commands is deter-

mined by instrument configuration. Generally, these commands are sent as one or more the device to perform a specific function. For example, FO is sent to the Model 775 to place the instrument in the fre-

ASCII

characters that tell

The preceding address groups are combined together to

form the Primary Command Group (KG). The bus also has another group of commands, called the Secondary Command Group (SCG). These are listed in Figure 3-3 for

informational purposes only; the Model 775 does respond to these commands, but other devices may have secondary addressing capability.

NOTE

Commands are normally transmitted with the 7.bit code listed in Figure 3-3. For most devices, the condition of D7 (DI08) is unimportant, as shown b> the “Don’t Care” indication in the table. Some devices, however, may require that D7 assumes ‘1 specific logic state before the commands are recognized.

Hexadecimal and decimal values for each of the commands or command groups are listed in Table 3-2. Each value in the table assumes that D7 is set to 0.

3-5

IEEE-488 OPERATION

Table 3-2. Hexadecimal and Decimal Command

Codes

Command 1 Hex Value*

GTL 01

SDC

GET

04 08

LLO 11

DCL

SI’E 18

SPD 19 LAG TAG UNL UNT

20-3F

40-5F

3F 5F

*Values shown with D,=O

Decimal Value

1 ii

20 24

25 32-63 64-95

3.6 COMMAND SEQUENCES

The proper command sequence must be sent by the controller before an instrument will respond as intended. The universal commands, such as LLO and DCL, require only that ATN be set low before the command is sent. Other commands require that the device be addressed to listen first, This section briefly describes the bus sequence for several types of commands.

3.6.1 Addressed Command Sequence

Before a device will respond to one of these commands,

it must receive a LAG cc.nmand derived from its primary address. Table 3-3 shows a typical sequence for the SDC

command. The LAG command assumes that the instru-

ment is set at a primary address of 23.

3.6.2 Universal Command Sequence

The universal commands are sent by setting ATN low and then placing the command byte on the bus. For example,

the following gives the LLO command:

ATEI.LLO

Note that both the ATN and LLO commands are on the bus simultaneously. Also, addressing is not necessary.

3.6.3 Device-Dependent Command Sequence

Device-dependent commands are transmitted with ATN high. However, the device must be addressed to listen fist

before the commands are transmitted. Table 3-4 shows the

sequence for the following command:

This command, which sets the Model 775 to the frequen-

cy A mode, is described in detail in paragraph 3.10.2.

Table 3~4. vpical Device-Dependent Command

Sequence

Data Bus

Step Command ATN State ASCII Hex Decimal

1 2 3

-5

*Assumes primary address=23

UNL Set low ? 3F

LAG* stays low

Data Set high F Data Stays high 0 Data Stays high X

7 37 55

46 70 30 58

Note that an UNL command is transmitted before the LAG, SDC sequence. This is generally done to remove all other listeners from the bus first so that only the addressed device responds.

Table 3-3. Qpical Addressed Command Sequence

Data Bus

Step Command ATN State ASCII Hex Decimal

UNL Set low ? 3F 63

3 4

*Assumes primary address=23

3-6

LAG* stays low

SDC stays low

Returns high

37 55

ELT 04 4

3.7 HARDWARE CONSIDERATIONS

Before the Model 775 can be used with the IEEE-488 bus, the instrument must be connected to the bus with a suitable connector. Also, the primary address must be properly programmed as described in this section.

3.7.1 ‘ly;plcal Controlled Systems

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

IEEE-488 OPERATION

Figure 3-3. Command Codes

3-7

IEEE-488 OPERATION

Figure 3-4 shows two typical system configurations. Figure 3-4(A) shows the simplest possible controlled system. The controller is used to send commands to the instrument, which sends data back to the controller.

The system becomes more complex in Figure 34(B), where additional instrumentation is added. Depending on programming, all data may be routed through the controller, or it may be transmitted directly from one instrument to another,

For very complex applications, a much larger computer can be used. Tape drives or disks can

then

be used to store

data.

Pigure 3-5. IEEE-488 Connector

MODEL 775

IA1 SIMPLE SYSTEM

CONTROLLER

ISI ADDITIONAL INSTRUMENTATION

CONTROLLER

Figure 3-4. System vpes

3.7.2 Bus Connections

The Model 775 is connected to the bus through an IEEE488 connector which is shown in Figure 3-5. This connector is designed to be stacked to allow a number of parallel connections on one instrument.

NOTE

To avoid possible mechanical damage, it is

recommended that no more than three connectors be stacked on any one instrument. Otherwise, the resulting strain may cause internal damage.

A typical connecting scheme for the bus is shown in Figure 3-6. Each cable normally has the standard IEEE connector on each end. The Keithley Model 7007 cable is ideal for this purpose. Once the connections are made, the screws should be tightened securely.~For the location of the connector on the rear panel of the Model 775, refer to Figure

3-7.

NOTE

The IEEE-488 bus is limited to a maximum of 15 devices, including the controller. Also, the maximum cable length is 20 meters. Failure to observe these limits will probably result in erratic bus operation.

NOTE

For control of possible radio frequency interference, a shielded IEEE488 cable (such as the Keithley Model 7007-1) must be used.

3-8

IEEE-488 OPERATIOI

INSTRUMENT

CONTROLLER

Figure 3-8. IEEE-488 Connections

Table 3-5. IEEE Contact Designations

contact

Number

1 2 3

z 6 7

10 ii

13 14 15 16 17 18 19 20 21 22 23 24

IEEE-488 Designation DIOl Data

D102 D103 Data D104 EOI (24) Management DAV Handshake NRFD NDAC IFC Management

SRQ

ATN Management

SHIELD D105 Data DI06 Data D107 Data DIOS REN (24) Management Gnd, (6) Ground Gnd, (7) Ground Gnd, (8) Ground Gnd, (9) Gnd, (10) Gnd, (11) Ground Gnd, LOGIC

Type Data

Data

Handshake Handshake

Management Ground

Data

Ground Ground

Ground

Figure 3-7. Rear Panel of Model 775 Showing IEEE

Connector

Custom cables may be constructed using the information in Table 3-5 and Figure 3-6. Table 3-5 lists the contact assignments for the various bus lines, while Figure 3-8 shows contact designations. Contacts 18 through 24 are return lines for the indicated signal lines, and the cable shield is connected to contact 12 and the connector shell. Each ground line is connected to digital common in the Model 775.

*Numbers in parentheses refer to signal ground return of

referenced contact number. EOI and REN signal lines return on contact 24.

CONTACT 12 CONTACT 12

CONTACT 24

CONTACT 1 CONTACT 1

CONTACT 12

Figure 3-8. Contact Assignments

3-9

IEEE-488 OPERATION

‘CAUTION The voltage between IEEE common and ground must not exceed 30V or damage to the instrument may occur.

A typical signal line bus driver is shown in Figure 3-9. With the configuration shown, the driver has bidirectional capability. When the 110 control line is high, the line is configured as an output line. When the control line is low, the driver is set up for input operation. Note that not all signal lines have bidirectional capability. Some lines, such as ATN, will always be configured as an output line in the controller and as an input line for all other devices on the bus.

DATA LINE

‘0 CONTROL

To check the present primary address:

1. Turn on the instrument.

2. The Model 775 wiB display the present primary address. For example, with the factory set value, the display will show the following:

IE Adr 23

This message will show on the display after a lamp test

is complete and the version of the software has been

displayed.

NOTES:

1. If a new address is set with the address switch on the rear panel, the instrument should be turned off and then on to activate the new address.

2. Each device on the bus must have a unique primary address. Failure to observe this precaution may result in erratic bus operation.

3.8 SOFTWARE CONSIDERATIONS

Figure 3-g. Typical IEEE-488 Bus Driver (One of 16)

3.7.3 Primary Address Programming

The Model 775 must receive a listen command before it

will respond to addressed commands. Similarly, the instrument must receive a talk command before it will transmit its data string, status word, or status byte. These listen and talk commands are derived from the instrument’s primary address. The Model 775 is shipped from the factory with primary address of 23. The primary address may be set to any value between 0 ad 30 as long as address conflicts with other bus instruments are avoided. This may be done by setting the address switch on the rear panel. Note that the primary address of the instrument must agree with the address specified in the controller’s programming language.

The most sophisticated computer in the world would be

useless without the necessary software. This basic requirement is also true of the IEEE-488 bus, which requires the use of handler routines as described in this paragraph.

3.8.1 Controller Interface Routines

Before a controller can be used with the IEEE-488 inter-

face, the user must make certain that appropriate handler

software is present within the controller. With the HP-85

computer,:for example, the HP-85 interface card must be

used with, an additional I/O ROM, which contains the

necessary ,handler software.

Other smd computers that can be used as controllers have

limited IEEE command capability. The I’ETKBM com-

puters, for example, are incapable of sending multiline

commands from BASIC, although these commands can

be sent through machine language routines. The

capabilities of other small computers depends on the par-

ticular interface being used. Often, little software “tricks” are required to achieve the desired results.

NOTE The programmed primary address is briefly displayed as part of the power-up cycle.

3-10

From the preceding discussion, the message is clear: make sure the proper software is being used with the instru-

IEEE-488 OPERATION

ment. Often, the user may incorrectly suspect that a hardware problem is causing fault, when it was the software that was causing the problem all along.

3.8.2 HP-85 BASIC Statements

Many of the programming instructions covered in this section use examples written in Hewlett-Packard Model 85 BASIC. The HP85 was chosen for these examples because it has a large number of BASIC statements that control IEEE488 operation. This section covers those HI-85 BASIC statements that are essential to Model 775 operation.

A complete list of HP-85 IEEE-468 BASIC statements is shown in Table 3-6. All the statements in the table have one or three digit arguments that must be specified. The first digit is the HP-85 interface select code, which is set to 7 at the factory. The last two digits of those statements that require a three digit argument specify the primary address Generally, only those commands that actually require an address to be sent over the bus require that the primary address be specified in the BASIC statement.

Those statements in the table with three digit arguments assume that the primary address of the device is set at 23. Other primary addresses require that the last two digits be set to the corresponding value. For example, to send a GTL command to device 22, the following BASIC statement would be used: LOCAL 722.

Some of the statements in the table have two forms; the exact configuration used depends on the desired command. For example, CLEAR 7 will cause a DCL to be sent, while CLEAR 723 causes an SDC to be transmitted to device 23.

The third column of Table 3-6 lists the mnemonics for the

command sequences. While most of these are covered elsewhere, a couple of points should be noted. As described earlier, the ATN line is set low by the controller if the data bus contains a multiline command. This is indicated in the table by ANDing the ATN mnemonic with the first command on the bus. For example, ATN*GET means that ATN and GET are sent simultaneously.

ABORT10 7 CLEAR 7 CLEAR 723 ENTER 723;A!$

LOCAL 723 LOCAL LOCKOUT 7 OUTPUT 723;A$

REMOTE 7 REMOTE 723

RESET 7 SPOLL(723)

TRIGGER 7 TRIGGER 723

Table 3-6. HP-85 IEEE-488 BASIC Statements

Action Send IFC.

Send DCL.

Send SDC to device 23. Device 23 addressed to talk. Data placed in AS. Send GTL to device 23. Send LLO. Device 23 addressed to listen. Transmit A$. Set REN true. Set REN true. Address device 23 to listen. Send IFC, cancel REN. Address device 23 to talk. Conduct serial poll. Send GET Address device 23 to listen. Send GET.

Bus Command

IFC ATN*DCL ATN*UNL;MTA;LAG;E ATN*UNL;MLA;TAG;ATN;data

ATN*UNL;MTA;LAG;GTL ATN*LLO ATN*MTA;UNL;LAG;ATN;data

REN REN;ATN*IJNL;MTA;LAG

1FC;REN;REN ATN*IJNL;MLA;TAG;SPE;ATN status byte;ATN*SPD;UNT ATN*GET ATN*IJNL;MTA;LAG;GET

Sequence

3-11

IEEE-448 OPERATION

Two commands not previously covered am MLA (My Listen Address) and MT4 (My Talk Address). These are ordinary PCG (Primary Command Group) addresses sent by the HI-85 to facilitate bus operation.

NOTE

The HE-85 address is set to 21 at the factory. Since

each device on the bus must have a unique primary address, do not program the Model 775 for the controller’s address to avoid possible conflicts.

3.8.3 Interface Function Codes

The interface function codes are part of the IEEE-4884978

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

Table 3-7 lists the codes for the Model 775. These codes

are also listed for convenience on the rear panel of the instrument immediately above the IEEE connector. The numeric value following each one or two letter code defines Model 775 capabilities as follows:

SR (Service~Request Function)-The ability for the Model 775 to request service from the controller is provided by the SR function.

RL (Ramota&cal Fun&on)-The ability for the Model 775 to be placed in the remote or local modes ls provided by the RL function.

PI’ (Parallel~Poll Function)-The Model 775 does not have parallel polling capabilities.

DC (Device Clear Function)-The ability for the Model 775 to be cleared (initialized) is provided by the DC function.

DT (Device Trigger Function)-The ability for the Model 775 to have its readings triggered is provided by the DT function.

(Contrder

troller capabilities.

TE (Extended Talker Capabilities)-The Model 775 does not

have extended talker capabilities. LE (Extended Listener Capabilities)-The Model 775 does

not have extended listener capabilities.

Function)-The Model 775 does not have con-

Table 3-7. Model 775 Interface Function Codas

SH (Source Handshake Function)-Ihe ability for the Model 775 to initiate the transfer of message/data on the data bus is provided by the SH function.

AH (Acceptor Handshake Function)-The ability for the Model 775 to.guarantee proper reception of message/data on the data bus is provided by the AH function.

T (Talker Function)-The ability for the Model 775 to send device-dependent data over the bus (to other devices) is provided by the T function. Model 775 talker capabilities exist only after the instrument has been addressed to talk.

L (Listener Function)-The ability for the Model 775 to receive device-dependent data over the bus (from other devices) is provided by the L function. Listener function capabilities of the Model 775 exist only after it has been addressed to listen.

Coda

SHl AH1 T6

SRl

RLl

IT0

DC1

LEO

Interface Function Source Handshake Capability

Acceptor Handshake Capability Talker (Basic Talker, Serial Poll, Unaddressed To Talk On LAG) Listener (Basic Listener, Unaddressed To Listen On TAG) Service Request Capability Remote/Local Capability No Parallel Poll Capability

Device Clear Capability Device Trigger Capability No Controller Capability Open Collector Bus Drivers No Extended Talker Capabilities No Extended Listener Capabilities

3-12

IEEE-488 OPERATION

3.8.4 Model 775 Interface Commands

Interface commands controlling Model 775 operation are

listed in Table 3-8. Not included in the table are device-

dependent commands, which are covered in detail in paragraph 3.10.

Table 3-8. IEEE Command Groups

HANDSHAKE COMMAND GROUP

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

UNIVERSAL COMMAND GROUP

ATN=ATTENTION DCL=DEVICE CLEAR IFC=INTERPACE CLEAR LLO=LOCAL LOCKOUT REN=REMOTE ENABLE SI’D=SERIAL POLL DISABLE SPE=SERIAL POLL ENABLE

ADDRESS COMMAND GROUP

LISTEN: LAG=LISTEN ADDRESS GROUP

MLA=MY LISTEN ADDRESS UNL=UNLISTEN

TALK: TAG=TALK ADDRESS GROUP

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

ADDRESSED COMMAND GROUP

ACGFADDRESSED COMMAND

GROUP

GET=GROUP EXECUTE TRIGGER

GTL=GO TO LOCAL

SDC=SELECTIVE CLEAR

STATUS COMMAND GROUP

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

Unaddressed Commands-No primary address is required for these commands. All devices equipment to implement these commands will do so simultaneously when the command is sent.

General bus commands are summarized in Table 3-9, which also lists the HI-85 BASIC statement that sends each command. Each addressed command statement assumes a primary address of 23.

NOTE

The Model 775 rear panel address switches must be set for a primary address of 23 to work with addressed command examples.

Table 3-9. General Bus Commands

/ Addressine / HP:85 BASIC

Command 1 Required 7 Statements

REN Yes

IFC

LLO NO

GTL Yes DCL No SDC Yes

GET* Yes GET* NO

*GET may be sent with or without addressing

1 REMOTE 723

ABORT10 7 LOCAL LOCKOUT 7 LOCAL 723 CLEAR 7 CLEAR 723 TRIGGER 723 TRIGGER 7

3.9.1 REN (Remote Enable)

The remote enable command is sent to the Model 775 by the controller to set the instrument up for remote operation Generally, this should be done before attempting to program the instrument over the bus. The Model 775 will indicate that it is in the remote mode by illuminating its front panel REMOTE indicator.

3.9 GENERAL BUS COMMAND PROGRAMMING

General bus commands are those commands which have

the same general meaning regardless of instrument configuration. These commands are grouped into two categories:

Addressed Commands-These commands require that the primary address of the instrument agrees with the primary address in the controller’s programming language.

To place the Model 775 in the remote mode, the controller must perform the following steps:

1. Set the REN line true.

2. Address the Model 775 to listen,

NOTE

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

3-13

IEEE-488 OPERATION

Programming Example-This sequence is automatically sent by the HP-85 when the following is typed into the keyboard.

After the END LINE key is pressed, the Model 775 REMOTE indicator light should come on. If not, check to see that the instrument is set for the proper primary ad-

dress, Also, check to see that all bus connections are tight.

3.9.2 IFC (Interface Clear)

The IFC command is sent by the controller to set the Model

775 to the talk and listen idle states.

To send the IFC command, the controller need only set the IFC line true.

After the END LINE key is pressed, the Model 775 is in the talk and listen idle states.

3.9.4 GTL (Go To Local)

The GTL command is used to take the instrument out of the remote mode. To send the GTL command, the controller must perform the ~following sequence:

1. Set ATN true.

2. Address the Model 775 to listen.

3. Place the GTL command on the bus

NOTE

The GTL command does not remove the local lockout state. With the local lockout condition

previously set, the GTL command will enable fmnt panel control operation until the next time 3 listener address command is received. This places the Model 775 in the local lockout state again.

Programming Example-If the instrument is not in the remote and lockout modes, enter the following statements into the HP-85 computer:

3.9.3 LLO (Local Lockout)

The LLO command is sent by the controller to remove the

Model 775 from the local operating mode. Once the unit receives the LLO command, all its front panel controls (except POWER) will be inoperative.

NOTE

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

To lock out the front panel controls of the Model 775, the controller must perform the following steps:

1. Set ATN true.

2. Send the LLO command to the instrument.

Programming Example-This sequence is automatically performed by the HP-85 when the following statement se-

quence is typed into the keyboard:

Check to see that the REMOTE indicator is on and that

the front panel controls are locked out. The CTL command sequence is automatically sent by the HP-85 with the following statement.

Note that the REMOTE Light on the front panel turns off.

Front panel control operation can be restored by setting

the REN line false with the following HP-85 statement:

After executing this statement, the front panel controls will again operate.

NOTE

Setting REN false with the LQCAL 7 statement will also take the instrument out of the remote mode.

314

3.9.5 DCL (Device Clear)

3.9.6 SDC (Selective Device Clear)

The DCL command may be used to clear the Model 775, setting it to a known state. Note that all e uipped to res

dll B

en the MO el 775 receives a DCL command, it will

return to the default, conditions listed in Table 34.0.

To send a DCL command, the controller must perform the following steps:

1. Set ATN true.

2. Place the DCL command on the bus.

ond to a DCL will do so simultaneously

devices on

the bus

Table 3-10. Default Conditions (Status Upon Power

Up or After SDC or DCL)

iraluc xi-

Frequency on channel A.

AC0

DC coupled on channel A.

AA0 xl attenuator on channel A.

AFO Filter off on channel A. Slope AS0 Coupling BCO Attenuator BAO xl attenuator on channel 8. Filter BFO 90 e

De ay IO Display Mode Data Format PO Reading with prefix, without

Displayed Digib EOI

SRQ Mask MOO Rate Sl Normal 3rdgs per second.

Terminator

Gate Time :i Delay Time

Trigger Level Trigger Level Totalize TOO Totalize A by B

Positive slope on channel A. DC coupled on channel 8.

Filter off on channel B.

BSO Positive slo P e on channel B.

Delay disab ed.

DO Display the measurement.

reading zero.

Set maximim displayed di its to 9

E81 enabled. SRQ disabled.

CR LF One second gate time.

One second delay time.

AU) ov

BIJI

The SDC command performs the same function as the DCL command except that only the addressed device

responds. This command is useful for clearing only a

selected instrument instead of all devices simultaneously.

The Model 775 will return to the default conditions listed

in Table 3-10 when responding to an SDC command.

To transmit the SDC command, the controller must perform the following steps:

1. Set ATN true.

2. Address the Model 775 to listen.

3. Place the SDC command on the data bus.

Programming

place the instrument in the frequency B measurement mode and enable the AC and filter modes. Now enter the following statement into the HP-85:

Note that the instrument did not respond because the SDC

command was sent with a primary address of 12. Now

enter the following statement into the HP-85 keyboard:

This time the instrument returns to the default conditions listed in Table 3-10.

Example-Using the front panel controls,

r;LE# ‘1”

I &

3.9.7 GET (Group Execute Trigger)

The GET command is sent to the Model 775 to arm the instrument. Using the GET command is only one of several methods that can be used to initiate readings. More detailed information on triggering including GET can be found in paragraph 3.lO.18.

Programming Example-Place the instrument in the frequency B measurement mode using the front panel controls. Also, enable the AC and filter modes. Now enter the following statement into the HP-85:

CLEAR 7

When the END LINE key is pressed, the instrument return? to power-up status.

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

1. Set ATN true.

2. Address the Model 775 to listen.

3. Place the GET command on the data.

GET can also be sent without addressing by omitting step

3-15

IEEE-488 OPERATION

Programming Example--Type in the following statement into the HP-85 keyboard:

REMOTE 723

Place the instrument in the one-shot on GET trigger mode with the following statement:

When the END LINE key is pressed, the GATE LED will

stop flashing and the HOLD LED will light indicating the instrument is waiting for a trigper.

The instrument may be triggered to take a single reading

with the following statement:

The GATE LED will flash once, indicating that one reading

has been processed.

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

3. The Model 775 is addressed to talk.

4. The controller sets ATN false.

5. The instrument then places its status byte on the bus to be read: by the controller.

6. The controller then sets the ATN line low and places

SPD (Serial Poll Disable) on the bus to end the serial polling sequence.

Steps 3 through 5 may be repeated for other instruments on the bus b using the correct talk address for each instrument. J A N must be true when the talk address is transmitted and false when the status byte is read.

Programming Example-The HP-85 SPOLL statement automatically performs the serial polling sequence. To demonstrate serial polling, momentarily power down the Model 775 and enter the following statements into the HP-85 keyboard:

NOTE

The Model 775 will also respond to GET without

addressing. This command is sent with the following HP-85 statement: TA Il;cER 7.

NOTE

The Model 775 will open the gate and complete

a reading, only if a signal is applied to the input and a proper trigger level has been set.

The preceding examples use device-dependent commands to place the instrument in the appropriate trigger modes. These commands are covered in detail in paragraph 3.10.

3.9.6 Serial Polling (SPE, SPD)

The serial polling sequence is used to obtain the Model

775 status byte. Usually, the serial polling sequence is used to determine which of several devices has requested service over the SRQ line. However, the serial polling sequence may be used at any time to obtain the status byte from the Model 775 for more information on status byte format, refer to paragraph 3.10.15.

The serial polling sequence is~ conducted as follows:

1. The controller sets the ATN line true.

When END LINE is pressed the second time, the computer performs the serial polling sequence. When END LINE is pressed the last time, the status byte value is displayed on the CRT. Paragraph 3.10.15 covers the status byte format in detail.

3.10 DEVICE-DEPENDENT COMMAND PROGRAMMING

IEEE-488 device-dependent commands are sent to the Model 775 to control various operating modes such as

function, trigger levels, gate time, filter and data format.

Each command is made up of an ASCII alpha character followed by one of more numbers designating specific parameters. For example, a function is programmed by sen-

ding an ASCII “F” followed by numbers representing the

function. The IEEE bus treats device-dependent commands as data in that ATN is high when the commands are transmitted.

A number of commands may be grouped together in one string. The Model 775 will ignore all nonprintable ASCII

characters (00 HEX through LF IHEX) and space character

(20 HEX) will be ignored. A command string is terminated

by an ASCII “X” character which tells the instrument to

execute the command string.

3-16

IEEE-488 OPERATION

If an illegal command or command parameter is present within a command string, the Instrument will:

1. Ignore the entire command string.

2. Display appropriate front panel emor messages.

3. Set certain bits In its status byte.

4. Generate an SRQ if programmed to do so.

These pro

3.10.15 an

I-IF-85 examples are included throughout this section to clarify programming.

Before performing a programming example, it is recommended that the instrument be set to its default values by sending an SDC over the bus. See paragraph 3.9.6 for information on using the SDC command.

If the HP-85 should become “hung up” at any point, operation may be restored by holding the SHIFT key down and then pressing RESET on the keyboard.

In order to send a device-de troller must perform the fo

amming aspects are covered in paragraphs

3.11.

NOTE

endent command, the con-

lr owing sequence:

1. Set ATN true.

2. Address the Model 775 to listen.

3. Set ATN false.

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

Pmgrammln sent by the I-K-85 using the following statement:

A$ in this case contains the ASCII characters that form the command string.

REN must be true when attempting to program the Model 775.

Commands that affect the Model 775 are listed in Table 3-11. All the commands listed in the Table 3-11 are covered in detail in the following paragraphs.

Programming Examples that follow assume that the Model 775 primary address is at its factory setting 23.

g Example-Daice-dependent commands are

NOTE

Mode Function

Coupling

Attenuator

Filter

Table 3-11. Device-Dependent Command Summary

Command

FO Frequency on Channel A ii

F3 F4 F5

;;

AC0 AC1 BCO BCl

AA0 AA1

BAO

BAl AFO

AFI

BFO BFI

Description Frequency on Channel B

Period on Channel A Period avera Time interva B Pulse on Channel A Frequency on Channel C Totalize on Channel A

DC coupled on Channel A AC coupled on Channel A DC coupled on Channel B AC coupled on Channel B

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

Filter Off on Channel A Filter On on Channel A Filter Off on Channel B Filter On on Channel B

e on Channel A

from A to B

3-17

IEEE.488 OPERATION

Table 3-11. Device-Dependent Command Summary (Cont.)

Table 3-11. Devlce-Dependent Command Summary (Cont.)

IEEE-488 OPERATION

Mode Self Test Data Control

Status Word

Execute

Command Description

uo Send operating mode status. Ul

X Execute other device-dependent commands.

Test ROM, RAM

Send measuring data string. Send gate time data string. Send delay time data string.

Send trigger level A data string. Send trigger level B data string.

Send error status.

3.10.1 Execute (X)

The execute command is implemented by sending an ASCII “X” over the bus. Its purpose is to tell the Model 775 to execute other device-dependent commands. Generally, the “X” character is the last byte in the command string.

NOTE

A command string sent without an execute character will not be executed at that time. but will be stored in the command buffer. The next time an execute character command is received, the stored commands will be executed, assuming all commands in the previous string were valid.

amming Example-Enter the following statements in-

I+%?

to the HP-85 keyboard:

FO=FREQ A Fl-FREQ B F2=l’ERIOD A F3=PERIOD AVG A M=TIME A-B F5=PLS A F6=FREQ C F7=Totalize

Upon power-up, or after the instrument receives a DCL or SDC command, the FO mode will be enabled.

Programming Example-Place the Model 775 in the fre-

uency A function from the front

ollowmg statements into the HP-8

me1 and enter the

keyboard:

REMOTE 723

rJlJTPlJT 723; 6 1 Xv 3

When END LINE key is pressed the second time, the front panel LISTEN LED flashes on then off, showing that the instrument received the command. No other changes will occur with this example because no other commands were given.

3.10.2 Function (F)

The function commands select the type of measurement made by the Model 775A. The eight parameters associated with the function comman d set the instrument to measure FREQ A, FREQ B, PERIOD A, PERIOD AVG A, TIME A-B, PLS A and Totalize, and with Model 7751 option installed, FREQ C. The function may be programmed by sending one of the following commands:

After the END LINE KEY is pressed the second time, the Model 775 will change to the period A function as shown by the PERIOD A indicator light.

3.10.3 Channels A, B Coupling (AC, BC)

The coupling command gives the user control over the in-

put coupling of the channel A and B inputs for the Model

775. The coupling may be programmed by sending one of the followmg commands:

ACO=DC coupling CHAN A ACl=AC coupling CHAN A BCO=DC coupling CHAN B BCl=AC coupling CHAN B

3-19

IEEE-488 OPERATION

Upon power-up, or after receiving a DCL or SDC, the in-

strument will be in the AC0 and BCO.

Programming Example-Select AC coupling with the front panel DC/AC button. Enter the following statements into HP-85:

When END LINE is pressed the second time, the AC LED indicator turns off and the instrument switches to DC coupling.

3.10.4 Channels A, B’Attenuator (AA, BA)

The attenuator command gives the user control over the

input attenuator mode of the channels A and B inputs for the Model 775. The attenuator may be programmed by sending one of the following cornman&:

AAO=xl attenuator AAl=xlO attenuator BAO=xl attenuator BAl=xlO attenuator

Upon power-up, or after receiving a DCL or SDC, the instrument will be in AA0 and BAO.

Programming Example-Select the X10 attenuator with the front panel ATTEN button. Enter the following statements into HP-85:

BFO=Filter off BFl=Filter on

Upon power-up, or after receiving a DCL or SDC, the in-

strument will be in AFO and BFO.

Programming Example-Select the filter off with the front panel FLTR button. Enter the following statements into HP-85:

When END LINE is pressed the second time, the FLTR

LED indicator turns on and the instrument switches the

filter on.

3.10.6 Channels A, B Slope (AS, BS)

The slope selection command gives the user control over the input slope mode of the channels A and B inputs for the Model 775. The slope may be programmed by sending one of the following commands:

ASO=I’ositive slope ASl=Negative slope BSO=I’ositive Slope BSl=Negative Slope

Upon power-up, or after receiving a DCL or SDC, the in-

strument will be in the AS0 and BSO.

Programming Example-Select the positive slope with the front panel SLOPE button. Enter the following statements into HP-85:

When END LINE is pressed the second time, the X10 LED indicator turns off and the instrument switches to Xl attenuation.

3.10.5 Channels A, B Filter (AF, BF)

The filter onioff~command gives the user control over the

input filter of the channels A and B inputs for the Model

775. Thea filter may be programmed by sending one of the following commands:

AFO-Filter off

.‘\Fl*Flter on

3.20

When END LINE is pressed the second time, the negative slope LED indicator turns on and the instrument switches to negative slope.

3.10.7 Channels A, B Trigger Level (AL, BL)

The trigger level selection command gives the user control over the input threshold point on the signal applied to the channels A and B inputs of the Model 775. The trigger mode may be programmed by sending a command using the following format:

IEEE-433 OPERATION

ALn BLn

Where n ls the trigger level in volts ln engineering format e.g. (<sign>D.DDE<sign>D). The sign and the exponent are optional. The trigger level may range from -2.55

to +2.55V in lOmV steps or from -25.5 to +25.5V in lOOmV steps. Selecting a trigger level in the range of -2.55V to

+2.55V will automatically set up the xl attenuator. Selec-

ting a trigger level in the range of -25.5V to +25.5V will

change the attenuator setting internally to the x10 at-

tenuator mode.

Upon power-up, or after receiving a DCL or SDC, the instrument will be in ALO and BU) (trigger levels at O.OOV).

Frogramming Example-Select the trigger level O.OoV by pressing simultaneously the LEVEL A and v buttons. Select xl attenuator mode. Enter the following statements into

HP-85:

REMOTE 723

OUTPUT723j“D3X”

OUTPUT723j“AL+l@.OX”

When END LINE is pressed the second time the Model

775 enters the trigger level display mode (More detailed

information on all display modes, including D3 can be found in paragraph 3.10.16). Observe that the trigger level on channel A is O.WV.

When END LINE is pressed the third time, the x10 in-

dicator turns on and the trigger level for channel A is set

to +lo.ov.

NOTE To increase flexibility, the Model 775 was designed in such a way to allow free format in programming the trigger level. In the previous example therefore, the last line may be replaced with one of the following lines:

3.10.8 Rate (S)

The rate command gives the user control over the measuring rate of the Model 775:Rate command parameters are summarized in Table 342.

The instrument will be in the Sl mode upon power-up, or after receiving a DCL or SDC command.

NOTES

1. The rate of transfer of information from the Model 775, depends to a great extent on the gate time. Table 3-12 lists the measuring rates, with the shortest gate time selected.

2. The data output format for the 53 mode is different from the data output format for all the other modes (More detailed information on data output format for the dump mode (S3), can be found in paragraph 3.11.5).

3. It may appear that GATE light does not flash when the fast rate mode (S2) is selected. This is because the microcomputer is busy performing the fast rate measurements and therefore cannot update the GATE light.

Table 3-12. Rate Commands

[ Process Time

Between

Command Mode Measuring Rate

so 1 Hold 1 One-shot on T, GET or]

external arming input.

Normal 3 readings per sec.

Fast*

25 readings per sec. wsmec “w.x

DunuP 140 readines oer sec.

Tan not be selected through front panel programming.

Measurements

W5smec max

5.5msec “lax

3-21

IEEE-488 OPERATION

Programming Example-Observe that the HOLD LED is off. If the indicator is on, press the MODE button on the front panel of Model 775 to turn the HOLD LED off. Enter the following statements into HP-85:

When END LINE is pressed the second time, the front panel HOLD LED will turn on, indicating that the oneshot mode is enabled.

3.10.9 Gate Time (G)

The gate time command controls the time that the gate remains open. The gate time may be programmed by sending a command using the following format:

G” Where n is the gate time in seconds in engineering for-

mat e.g. (DE <sign>D). The sign and the exponent are optional. The allowable values for gate time are listed in Table 34.3.

NOTE

To increase flexibility, the Model 775 was designed in such a way to allow free format in programming the gate time. In the previous example therefore, the last line may be replaced with one of the following lines:

3.10.10 Delay Time (W)

The delay time command controls the amount of delay in

closing the gate after the gate was (pen. The delay time mode may be programmed using a command with the following format:

Where n is the delay time is seconds in engineering format e.g (DE < sign > D). The sign and the exponent are op-

tional. The allowed values for delay time are listed in Table

3-n

Upon power-up, or after receiving a DCL or SDC, the instrument will be in the Gl mode, with a gate time of one second.

The gate time may be programmed to the external user gate time by sending a command using the following format: GU.

Programming Example-Select the frequency A function, then select the gate time of one second by pressing simultaneously the GATE/DELAY TIME A and V buttons on the front panel. Enter the following statements into HP-85:

When END LINE is pressed the second time the Model 775 enters the gate time display mode. (More detailed in-

formation on all display modes; including Dl, can be found

in par;;raph 3.10.16.) Observe that the gate time is one se-

cond. When END LINE is pressed the third time, the gate

time

is set to 500msec.

Upon power-up, or after receiving a DCL or SDC, the instrument will be in the Wl mode (delay time of one second).

The delay time may be programmed to external delay by sending a command using the following format: WU

Programming Example-Select TIME A-B function, then select a delay time of one second by pressing simultaneously the GATE/DELAY TIMP A and V buttons on the front panel of the Model 775. Enter the following statements into the HP-85:

When END LINE is pressed the second time the Model 775 enters in delay time display mode. (More detailed information on all display modes; including D2,

can

be found in paragraph 3.10.16). Observe that the delay time is one second. When END LINE is pressed the third time, the delay time is set to 30msec.

3-22

IEEE.488 OPERATION

NOTE To increase flexibility, the Model 775 was designed in such a way to allow free format in programming the delay time. In

the

previous example therfore,

the last line may be replaced with one of the following

lines:

OUTPIJT 723) 6 6 W30E-3x9 ’

CllJTPUT 723; 6 ~11013WMB8, BO@!43E3::<7 ’

UUTPUT723;“W3E-2N?’

Table 3-13. Gate/Delay Time Predetermined

lsec

2sec 3sec 4sec 5sec 6sec

7sec

3.10.11 Delay (I)

Where n may have any value fom 3 to 9.

Upon power-up, or after receiving a DCL or SDC, the instrument will be set to N9.

Programming Example-Select the frequency A function, then select the gate time of one second by pressing simultaneously the GATE/DELAY TIME A and 7 buttons.

Press simultaneously the GATE/DELAY and TRIGGER LEVEL DISPLAY buttons and then, press simultaneously the GATE/DELAY TIME A and v buttons. This will set up the Model 775 to display nine digits. Press any pushbutton on the front panel of the Model 775 to return to the normal display mode. Apply a signal to the channel A input of Model 775 and observe that the frequency of the signal will be displayed with at least eight digits. Enter the following statements into the HP-85:

REMOTE 723

l:llJTPlJT 723; i i ,,,L$><’ 1

The delay command gives the user control over the delay

mode. The delay mode inay be programmed by sending one of the following commands:

IO=Delay off Il=Delay on

Upon power-up, or after receiving a DCL or SDC, the in-

strument will be in the IO mode.

Programming Example-Select TIME A-B function, then

select the delay off mode with the front panel MODE but-

Len. Enter the following statemen’s into the HP-85:

REIIOTE 723

ICIJTPIUT 723j 6 1 II:):? 9

When END LINE is pressed the second time, the DELAY LED indicator turns on and the instrument switches to the delay on mode.

3.10.12 Displayed Digits (N)

The displaved digits function sets the maximum number of digits that the Model 775 will display. To program the

number of digits send the folIowing command:

When END LINE is pressed the second time the measured frequency will be displayed with maximum four digits.

3.10.13 Triggering (T)

The “T” and GET commands are used to trigger the Model 775 over the IEEE bus (see GET 3.9.7). Triggering arms a measurement cycle. In the continuous mode, the Model 775 is always armed. In the one-shot mode (SO), a separate trigger stimulus is required to arm each measurement cycle.

Programming Example-Place the Model 775 into mode. Using the MODE button on the front panel of the Model 775, apply a signal to the channel A input of Model 775 and observe that the GATE LED ,indicator is not flashing, indicating the instrument is waiting for a trigger. Enter the following statements into the HP-85:

When END LINE is pressed the second time the GATE indicator flashes once, indicating one reading has been processed. To continue taking readings in this mode, a bigger is needed for each measurement cycle.

the hold

3.23

IEEE-488 OPERATION

3.10.14 EOI (K)

The EOI line on the bus is usually set low by the device

during the last byte of its data transfer sequence. In this way, the last byte is properly identified, allowing variable length data words to be transmitted. The Model 775 will normally send EOI during the last byte of its data string or status word. The EOI response of the instrument may be sent with one of the following commands:

KO=Send EOI during last byte. Kl=Send no EOI.

Upon power-up, the K!J mode is enabled.

Programming Example-The Model 775 EOI response will be suppressed with the following HP-85 statement sequence:

NOTE

HP-85 does not rely on EOI to mark the last byte of data transfer. Some controllers, however, may require that EOI be present at the end of transmitting.

3.10.15 SRQ Mode (M) and Serial Poll Status Byte Format

The SRQ comntand controls which of a number of conditions within the Model 775 will cause the instrument to request service from the controller with the SRQ line command. Once a SRQ is generated, the Model 775 status byte can be checked, via serial polling (see paragraph 3.9.8), to determine if it was the Model 775 that requested service. Other bits in the status byte could also be set depending on certain data or error conditions.

TheModel77Scanbe one or mans of the following conditions.

1. If a reading has been completed.

2. If an overflow condition ocm.

If en error condition caxrs.

4. lf a self test has

5. If the Model 775 is ready to receive device-dependent commands.

Upon power-up, or after a DCL or SDC command, SRQ

is disabled.

SRQ Mask-In order to facilitate SRQ programming, Model 775 uses an internal mask to generate the SRQ. When a particular mask bit is set, the Model 775 will send a SRQ when those conditions occur. Bits within the

can

be controlled by sending the ASCII letter “M” followed by a decimal number to set the appropriate bits. Table 3-14 lists the commands to set the various mask bits, while Table 3-15 lists all legal SRQ mask commands.

ProgammedtogenemteSRQun~

been

completed.

the

mask

Table 314. SRQ Mask Commands

Condition to

Command

Ml MT!

M8 Ml6 M32

Sets Bit Number

BO (LSB)

Bl 83

t----l

B4 B5

Generate

Overflow Self-test done Reading done Ready Error

--I

SRQ

3-24

IEEE-488 OPERATION

Table 3-15. SRQ Mask Legal Commands

Rit Number I B5 1 84 1 83 I 82 1 Bl 1 BO fLSBI

Command

MO Ml M2

Kl Ml1 Ml6

Ki Ml9

M24

M25 M26 M27 M32 M33

E M40

M41 M42 M43

kiti MS0

M51

M56

M57

M58

M59

Reading

Error Ready

Done

No No NO No No NO No No

NO No No NO No No

Yes No No Yes No No

Yes No No Yes NO Yes No

Yes EE NO

Yes rJ:

Yes NO NO Yes Yes No Yes NO Yes

Yes Yes

NO Yes Yes Yes No Yes No Yes No Yes No

NO NO NO

No Yes No Yes Yes No Yes Yes No Yes No

Yes

Yes Yes Yes NO Yes Yes

Yes Yes

Yes Yes NO Yes Yes Yes Yes Yes Yes Yes

Yes Yes

Yes Yes Yes

Self-Test

Done

NO NO Yes Yes NO NO Yes Yes NO NO Yes Yes

NO Yes Yes

E Yes Yes

NO Yes Yes

Overflow

Yes

Yes,

Yes

NO Yes NO Yes No Yes NO Yes NO Yes NO Yes NO Yes

NOTE

There are 32 legal SRQ mask commands that are

possible with the Model 775. Table 3-15 lists all

combinations. (e.

request service afi

. selecting MlO, Model 775 will er one reading is complete or

a self-test occurs.)

Status Byte Format-The status byte conGns information relating to data and error conditions within the instrument. Table 3-16 lists the meaning of the various bits. The status byte is obtained by using the WE, SPD polling sequence described in paragraph 3.9.8.

IEEE-488 OPERATION

Bit Number 87 (MSB) B6 B5 B4 B3 82 Bl BO (LSB) 1

Interpretation 0

Table 3-16. Status Byte Interpretation

Reading Self-Test

RQS Error Ready Done

0 Done Overflow

The various bits in the status byte are described below:

1. Overflow-When measuring a time interval larger than 1OOOOsec in SO, Sl and S2 modes, the overflow bit will

be set. In S3 mode, the overflow bit will be set when measuring a time interval larger than 9msec or measuring frequency and PERIOD AVG A with a gate time larger than 9msec. This bit is cleared after the Model 775 is addressed to talk in the BO mode.

2. Self-Test Done-Set after power-up self test completion

or after executing the self test (J) command. This bit is cleared by reading the error status word (Ul).

3. Reading Done-Set after completion of a measurement cycle. The reading done bit is cleared after the Model 775 is addressed to talk in the BO mode.

4. Ready-Set after power-up. This bit is cleared when the Model 775 receives an execute command (X) and is reset after the instrument completes the command (Mode1 775 is ready for the next command string).

5. Error-Set if an illegal command has been received or gate error has occurred in the last measurement cle. This bit is cleared by reading the error status word 7 Ul).

6. RQS-Model775 will set this bit if one or more condi-

tions for service request occur, and the SRQ mask, for at least one of these service request conditions is enabl-

ed. This bit is cleared by reading the status byte using

the WE, SPD pollin: sequence.

Programming Example-Enter the following program into the HP-85:

PROGRAM

Press the HP-85 RUN key. The computer conducts a serial poll and displays the status byte bits in order on the CRT. The SRQ (B6) and the Error (B5) bits are set because line 30 of the program attempts to program the instrument with an illegal command option (F7). The Model 775 will then respond with an IddCo Err message which will be diplayed for about one second.

COMMENTS

eration.

Proeram for SR on

error. Attempt to program illegal command option. Perform serial poll.

NOTES

1. Once the Model 775 has generated an SRQ, its status byte should be read to clear the SRQ line. Otherwise

the instrument will continuously assert the SRQ line.

2. The Model 775 may be programmed to generate an SRQ for more than one condition simultaneously. For exam-

ple, to set SRQ mask bits for an SRQ if an error occurs

and when an overflow condition occurs, the following command would be sent: M33X. All possible mask combinations are listed in Table 3-15.

3. If the instrument is programmed to generate an SRQ when a reading is done, it will generate the SRQ only

once when the reading is complete; the SRQ may be cleared by reading the status byte. The reading done bit

in the status byte may then be cleared by requesting a normal reading from the instrument.

3.26

3.10.16 Display Modes (D)

The display command controls what the Model 775A places on the display. The six parameters associated with the display command set the instrument to display the measurement, gate time, delay time, trigger levels, totalize gate option or an ASCII message. The display mode may be programmed by sending one of the following commands:

DO=Measurement Dl=Gate Tie D2=Delay Time D3=Trigger Levels D4=Totalize gate option D5=ASCII message

IEEE-488 OPERATION

In the D5 display mode, the ASCII message that can be placed on the Model 775A display is limited by the capabilities of the seven segment readout, but; even with those limitations, considerable versatility is possible.

NOTES

1. The maximum number of characters that can be sent

with the D5 command is 10. Any additional characters will be ignored.

2. Display position 10 (the second position from the right on the displa ) is not used in this mode because of its limited possi&ities.

3. Any undisplayed character will appear as an underline

segment.

4. Decimal points are set on the current display position,

if possible, and do not advance the display to the next position.

5. Sending a “D5X” command will blank out the display.

6. The “DOX” command restores the display to normal (measurement) operation.

Pmgramming Example-Enter the following statements into the HP-85 keyboard:

When the END LINE is pressed the second time, the instrument performs the self-test, The result of the self-test may be checked by reading the Ul error status word. A detailed description on the Ul error status word and how to read it is given in paragraph 3.11.2.

3.10.18 Totalize (TO)

The totalize command allows the user to select between two gating options: Total&e A by B and cumulative totalize. Totalize A by B allows the user to limit the amount of time that pulses are counted; where as, the cumulative totalize command allows an infinite gate time. The totalize gate option may be programmed by sending one of the following commands.

TOO=Totalize A by B TOl=Cumulative totalize

NOTE: The TO command only selects the gate option. The F7 command must also be used to select the totalize function.

Upon power up, or after receiving a DCL or SDC, the in-

strument defaults to TOO.

REMOTE 723

When END LINE is pressed the second time, the “HELLO-775” message will be displayed.

3.10.17 Self-Test (J)

The J command causes the instrument to perform ROM and RAM tests similar to the power-up procedure tests. When the self-test command is given, the Model 775 performs the following tests:

1. RAM test

2. ROM test

The J command has no parameters. When the test is complete the SELF TEST DONE bit in the status byte is set, and if the SRQ mask bit for self test done is set, the Model 775 will request service. If the self-test is successful, the

SELF TEST bit in the Ul error status word (see paragraph

3.11.2) will be a 0. Otherwise, this bit will be a 1.

Pro

amming Example-Enter the following statements in-

to t e HP-85:

REtWTE 723

QIJTPIJT 723; 1 1 .JX’ 9

Programming Example-With the Model 775A in the

Totalize A by B mode, enter the following statements into

the HP-85 keyboard.

REIIOTE 723

I:IIJTPI~IT 723.: 6 i FTTljl::” 7

After the END LINE key is pressed a second time, the Model 775A will change to the cumulative totalize mode.

3.11 READING FROM THE MODEL 775

The reading sequence is used to obtain from Model 775

various information strings such as measurement, gate time, delay time and tri is made up of ASCII alp PB For more details on the information string format refer to paragraph 3.11.1.

The reading sequence is conducted as follows:

1. The controller sets the ATN line true.

2. The Model 775 is addressed to talk.

3. The controller sets ATN false.

4. The instrument sends the information string over the bus one byte at a time.

5. The controller recognizes that the string is terminated.

6. The controller sets the ATN line true.

7. The LINT (untalk) command is placed on the bus by the controller.

er levels. Each information string

a and alphanumeric characters.

3.27

IEEE.488 OPERATION

NOTE Most controllers use the CR (Carriage Return) or LF (Line Feed) character to terminate their input sequences, but other techniques may be used as well to recognize the end of input sequence (e.g. EOI line is low on the bus during the transfer of the last byte).

Programming Example-The command sent by HP-85 to request the data string from the Model 775 has the following format:

EHTER 723; kb

DISP AB

zi$$his case contains ASCII characters that form the data

Upon power-up, or after the instrument receives a DCL or SDC command, the Model 775 will respond to a request for a data string by sending the data string contained in the measuring buffer. This data string is sent only once

for each measuring cycle. After this string has been sent,

the next re pletion of t

uest for a data string will be delayed until com-

e next measurement cycle. The data format

for the measuring string is described in Table 3-V.

To read other strings of information besides the measur-

buffer,

to %

e sent by the controller. This is covered in detail in the

a data control device-dependent command has

following paragraph.

3.11.1 Data Control Commands (6)

The data control commands allow access to information

concerning the present operating conditions of the instru-

ment. When the data control command is given, the Model 775 will transmit the associated data string instead of its normal data,string the next time it is addressed to talk the Model 775 data control commands include:

BO=Normal data string (measuring buffer) Bl=Gate Time string B2=Delay Time string B3=Trigger Level A string B4=Trigger Level B string

Table 3-B’ shows the general data string format for each of five commands,

NOTES

1. Data strings have fixed length of 14 ASCII characters for the BO command without the prefix and terminator. For all other data strings (Bl, 82 83 and B4), the length of the data string is five ASCII characters without the prefix and terminator. If the data string is sent with a prefix,

four additional ASCII characters are included (refer to paragraph 3.11.4). If the data string is sent with one or two terminators, the length of the data string increases by one or two characters respectively. If the Model 775 was programmed to the S3 measuring rate (see paragraph 3.10.13), the 80 data string is no longer ASCII characters but 12 binary coded digits (BCD), incor-

porated into six bytes. See paragraph 3.11.5 for detailed information on using the dump mode (S3).

2. All data string information, besides the normal data

string, will be sent only once each time the command is sent. Once the data string is read, the instrument will

send its normal data string the next time it is addressed to talk.

3. To ensure that the correct data string is received, the data

string should be read immediately after sending the command, to avoid having an incorrect data string

transmitted.

3.28

Table 3-17. Data String Format

Data String Format* Description (orefix)+1.23456789E+OfCR LFI 1 Normal Data Strine**

~ATE;IE+o(CR LF) ~ ’ Data String Formarfor Gate Time GATE=USER (CR LF) DLAY+lE+O(CR LF) DLAY=USER (CR LF) TRGA+O.OO (CR LF) TRGB+O.OO (CR LF) Data String Format for Trig Level B

*CR LF is normal terminator. The terminator may be changed (see paragraph 3.11.3):

The prefixes are listed in Table 3-28.

W format is valid for all measuring rates except for the S3 rate mode. S3 mode is covered

in more detail in paragraph 3.11.5.

Data String Format for Delay Time Data String Format for Trig Level A

Table 3-18. Pdlxes

Data String Prefixes Description

The prefix defines a normal or overflow reading as well as the measuring

function. If a reading is overflow. N- prefix become 0- and the number is set to: +9.99999999E+9.

NTRA l

NFRB l FREQ B measurements NPER * PERIOD A measurements

NAVG * PERIOD AVERAGE A measurements

NWB * TIME A - B measurements NPLS * PULSE A measurements NFRC * FREQ C measurements

FREQ A measurements

IEEE-488 OPERATION

Example-Enter the following program in-

iIziE%?

PROGRAM

10 REMOTE723

2B OUTPUT723i

~‘BiX”

39 ENTER 723; A 40 DISPAS

5B END

Press the HP-g5 RUN key. The computer reads and dtsplays the gate time string.

COMMENTS

Set up remote operation. Program Model 77.5 to send the gate time data string. Enter reading into computer.

Display reading into

computer.

Display on CRT

3.11.2 Status Word (U)

The status word commands allows access to information concerning present operating modes and the error history of the instrument. When the status word command is given, the Model 775 will transmit the appropriate status information instead of its normal data sting the next time it is addressed to talk. The Model 775 status word commands include:

UO-Operating mode status word Ul=Error status word

Table 3-19 shows the general format for each of the status words.

3.29

IEEE-488 OPERATION

Command 1 Status Word Format

Table 3-19. Status Word Formats

775FACAAAFASBCBABFBSIDl’NKM*SYTO(CRLF)

CR LF is normal terminator. The terminator may be changed (see paragraph 3.11.3).

“The UO status word sends 2 bytes for the M status and 1 byte for all others.

1 775 IDDC IDDCO GATEERROR SELFI’EST 0 0 0 0 0 (CR LF)

NOTES

1. Status word information will be returned only once each time the command is sent. Once status is read, the in-

strument will send its normal data string the next time

it is addressed to talk.

2. To ensure that the correct status is received, the status

word should be read immediately after sending the command, to avoid having an incorrect status transmitted.

3. The status word should not be confuged with the status

byte. The status word contains a string of bytes pertaining to the various operating modes of the instrument.

The status byte is a single byte that is,read with the SPE,

SPD command sequence and contains information on SRQ status.

The retimed Ul value is 1 for an IDDC error, for an IDD-

CO error, for a GATE ERR that occurs after the Ul status

word has been cleared the last time and if the self test

failed.

5. Ul error status word is cleared by reading Ul status

word. Reading this status word also clears the self test done and the error bits in the SRQ status byte (see paragraph 3.10.15).

3.11.3 Terminator (Y)

To allow for a wide variety of controllers to be used, the

terminator can be changed by sending an appropriate command over the bus. The default value is the commonly used carriage return, line feed (CR LF) sequence (mode YO). The terminator sequence will assume this default value upon power-up, or after receiving a DCL or SDC. The terminator for the Model 775 may be programmed by sen-

ding one of the following commands:

YO=(CR LF) Yl=(LF CR) M=(CR)

M=(LF) Y4=No terminator

NOTE

Most controllers use the CR or LF character to terminate their input sequence. Using the no terminator mode Y4 may cause the controller to hang up unless special programming is used.

Programming Example-Enter the following program into the HP-85:

PROGRAM

Press the HP-85 RUN key. The computer reads and &plays the error status word.

3-30

COMMENTS

Set up remote operation. Program Model 775 to send the error status word. Enter reading into computer. Display on CRT.

Programming Example-The terminator can be eliminated

by sending the following HP-85 statements:

When END LINE is pressed the second time, the terminator is suppressed; no terminator will be sent by the instrument when data is requested. The absence of the normal terminator may be verified by entering the following statement into the HP-85 keyboard:

At this point, the HP-85 ceases to operate because it is waiting for the standard CR LF terminator sequence to terminate the ENTER statement. The computer may be reset

by holding down the Sm key and then pressing RESET

IEEE-488 OPERATION

on the keyboard. To return the instrument to normal terminator sequence, enter the following statement into HIVE:

OUTPUT723;“YBX”

3.11.4 Prefix (P)

The prefix on the data string may be suppressed using this command. When the prefix is suppressed the output data

string is four bytes shorter. The P command is also used to replace leading space character (ASCII 20 HEX) in the data string with character 0 (ASCII 30 HBX). For some controllers an attempt to read a number, instead of a string, will result ln a reading error because of its inability to read

the spaces before the first significant dlglt. To eliminate thls problem, the Model 775 should be programmed to send the data string with leading zeros. P command parameters incude:

PO-With prefix, without leading zero PItWithout prefix, without leading zero P2-With prefix, with leading zero P3-Without prefix, with leading zero

Pmgrammlng Example-Enter the following program in-

to the HP65:

PROGRAM COMMENTS

10 REMOTE723

20 OUTPUT723i

‘ ‘ P3B0X’ ’

30 ENTER723iA9 40 DISPM

50 END

Press te HP-85 RUN key. The computer reads and displays the data string without prefix and with leading zeros.

Note that in the previous pmgramming example two device-dependent commands have been sent in the same command string.

Set up remote operation. Program Model 775 to send the data string without urefix and with leading zeros. Enter reading into

NOTE

3.11.5 Dump Mode (53 Rate Mode)

The 53

put Model 775 readings to the bus at an extremely fast rate or to analyze raw measurement data. In this mode the processing and the display cycles are bypassed and a “busy’ message is displayed on the front panel. Table 3-20 lists the dump mode specifications and considerations. When Model 775 is addressed to talk, the instrument sends a data string of 12 binary coded digits (BCD), in six bytes plus

the terminator if the instrument is in the YO, YI, Y2 or Y3 terminator modes. The first six BCD digits are from the

TIh4B register and the other six BCD digits are from the

EVENT register.

Table 3-21 lists the formulas which are used to calculate

the result for the different functions. Examples for some calculations are also given.

PROGRAM

rate mode may be used when it is desired to out-

COMMENTS

Program to exercise binary dump of 775

D=723

DItlGsC331~k$

ClllrA(8)

REMOTE D

INPUT GO

OUTPUT D i G$

P=SFOLL t::Dl

DI:;P 6 6 !;pljLL=” 9 .: F

56 60

ENTER Di A9

FOR I=1 TO E,t?iUI::s

=NUM IQ$[ I];tlG! NEXT

I=1 @ GO!jllEl 2001E

T=R

I =4

‘8

;0 71

13 GO!:IJB 2MO@

E=R F=lcJ vE:Tc:E/T) DI!;;F G ‘FF:E,;!=’ f ,; F

DI::;F d c L::;D ,:,F F’E!XILIJTII:IN= ! ,i

F...~T

DISF ‘ L E,.,,T =“jE;“,,,;T

GOTU 40

Configure 775 suggest

“G.OOlS3X”.

80 is OFLO bit. Binary equivalent of

BCD string. Decimal time value. Decimal event count.

Packed BCD to decimal.

200

R=0

FOR N=2 TO 0 STEP

202

-1

R=R+Ck(I+N)MOD

lb+AcI+N>DIU 16*10)*10 vc2*

(2-N)) NEXT N

225 230

RETURN

3-31

IEEE-488 OPERATION

Device-depedent Command: S3 Display During Dump: bu,SY Processing Time

Between Measurements: Data Transfer:

Minimum ReadingslSec: Maximum ReadingslSec: Operational Functions

Disabled During Dump: Data Format:

Output Format:

Table S-20. Dump Mode Specifications

Lass than 5.5msec (measurement processing and display are suppressed).

Controller speed dependent (2.75msec using PSI 80,. -

40 (with a gate time of 9.99999msec). 140 (with a gate time of 100ssec). Normal display, external trigger.

BCD except terminator.

T5,T4 T3,TZ Tl,lU E5,E4 E3,E2 El,EO

first byte

I-

last byte -

Interpretation:

Gate Time Limits:

Overflow Indication:

Conditions that cause overflow:

1. Gate-time longer than 9.99999msec.

2. Ir FREQ A or B and PERIOD AVG when maximum frequency x gate time is greater than 999,999, but under no condition should gate time be longer than 9.99999msec.

3. In TIME INTERVAL A to 8, PERIOD A and PULSE A + delay time longer than 9.99999msec.

4. In FREQ C when frequency/256 x gate time is greater than 999,999.

T5-IB=TIME REGISTER E5-EO=EVENT REGISTER

1OOssec to 9msec with internal gate-time. 1OOFsec to 9.99999msec with external gate-time.

999999 in either time or event registers. Overflow bit in the SPOLL byte is set, RQS in Ml mode.

3-32

IEEE.488 OPERATION

Dump Output Mode Calculation lhamplee: Frequency

Mode: FOG%3Y4S3X output:

Time Register: 089852 Event Register: 000005

5 x 108

Frequency: =

5564m6407h

89852

5564.mcm

*LSD: = 0.061931914Hz

89852

This is rounded to O.lHz. Adjusted Frequency Reading: 5.5647R+3Hz.

Period

Period Averaged

Mode: F3GlE-3Y4S3X OUtpUt:

lo1 121 64 1001 03109

Tie Register: 101264 Event Register: OOtl309

Ml264 x lo-’

Period Averaged:

= 3277l52104 x 10

309

3277152104 x 1O-1

*LSD:

= 0.003236245 x lo-

101264

This is rounded to .Ol x lO+. Adjusted Period Averaged Reading: 327.7lE-6s~.

Frequency C

Mode: F2Y4S3X output:

I73 22 1781 001 001 00 I

Time Register: 732273 Event Register: 0

Period: 732273 x W Adjusted Period Reading: Z32278E-3sec.

Mode: F6G9E-3Y4S3X output:

901 171 891 031 73 06

Time Register: 901789 Event Register: 037306

256 x 37306 x lOa

Frequency: = 10.5904565 x lO*H

901787

10.5904565 x lOa

*LSD: = 0.00001174 x 10BHz

901787

Thrs IS rounded to 0.00001 x 108Hz

I ”

Adjusted Frequency Reading = l.O59045E+9Hz

*LSD is the least significant usable digit.

3-33

IEEE-488 OPERATION

,,, .Table 3-21. Dump Output Mode Result

3.12 FRONT PANEL ERROR MESSAGES

The process of programming the Model 775 involves the proper use of syntax. Syntax is defined as the orderly or systematic arrangement of programming commands or languages. The Model 775 must receive valid commands with proper syntax or it will:

CalCuhtlOn

3.12.1 IDDC Error

An IDDC error results when the Model 775 receives an

invalid command such as ClX. This command is invalid

because no such letters exists in the instruments ptogram-

ming language.

1. Ignore the entire command string in which the invalid command appears.

2. Set appropriate bits in the status byte and error word.

3. Generate an SRQ if programmed to do so.

4. Display an appropriate front panel message.

Device-dependent co ASCII characters. Some examples of valid command strings include:

FOX Single command string. FOD282X Multiple command string. Bl X Space is ignored.

Examples of invalid command strings are: COX Invalid command; C is not a command.

F8X Invlaid command option; 8 is not an option of the F command.

Figure 3-10 shows the front panel error messages employed by the Model 775. The messages in Figure 3-M(a) results from an Negal Device-Dependent Command @DC), while the message in Figure 3-10 (b) results from an Illegal Device-Dependent Option (IIDCO).

mmands are sent as a string of several

Programming Example-To demonstrate an IDDC enter the following statements into the HP-85 keyboant:

REMOTE 723

OUTPUT723~“CiX”

When END LINE is pressed the second time, the error message in Figure 3-u) (a) is displayed for about one second.

3.12.2 IDDCO Error

An IDDCO error occurs when the numeric oarameter

associated with a legal command letter is in&d. For example, the command D7X has an invalid option because the instrument has no display mode associated with that number.

Programming Example-To demonstrate an IDDCO error enter the following statements into the HP-85 keyboard;

REMOTE 723

OIJTPUT 723 i ‘ @ D7X’ ’

When END LINE is pressed the second time, the error message in Figure 3-10(b) is displayed for about one

second.

3-34

A. ILLEGAL-DEVICE DEPENDENT COMMANDS IIDDC)

(--mJml

S. ILLEGAL DEVICE-DEPENDENT COMMAND OPTION IIDDCO)

Figure 3-10. IEEE-488 Display Error Messages

IEEE-488 OPERATION

3.3513.38

SECTION 4

PERFORMANCE VERIFICATION

4.1 INTRODUCTION

This section contains information necessary to verify that the Model 775 is performing within the specified accuracy. The Model 775 specifications may be found preceding Section 1 of this manual. Ideally, performance verification should be performed when the instrument is first received to ensure that no damage or change in calibration has occurred during shipment. The verification procedure may also be performed whenever instrument operation is suspect or following calibration. If performance on any of the functions is substandard, adjustments can be performed as described in Section 6.

NOTE

If the instrument does not meet specifications and it is still under warranty (less than 12 months since date of shipment), contact your Keith@ representative or the factory to determine the action to be taken,

4.2 ENVIRONMENTAL CONDITIONS

4.3 RECOMMENDED TEST EQUIPMENT

Recommended test equipment for the Model 775 performance verification is listed in Table 4-l. Different equipment may be used as long as the accuracy specifications are equal or exceed the specifications listed in Table 4-l.

4.4 INITIAL CONDITIONS

Before performing the verification procedures, make sure the Model 775 meets the following conditions:

If the instrument has been subject to temperatures below 0°C or above 50°C, allow sufficient time for the instrument to reach temperatures within the range.

Generally, it takes one hour to stabilize an instrument

that is WC (18°F) outside of this range.

Turn on the power to the Model 775 and allow it to warm-up for at least two hours before beginning the verification procedure.

4.5 VERIFICATION PROCEDURES

All measurements should be made at an ambient temperature between 0 and 40°C with a relative humidity of less than 80%.

Table

Instrument Model

Oscilloscope Multimeter

Synthesized Signal Generator Marconi 2019 Function Generator 1OMHz Standard

4-1. Recommended Test Equipment For Performance Verification

Recommended Tektronics 465

Keithley I75 HP-33I2A

Oscilloauartz 2200 10~Vdav, 5x10-‘” 0-50°C

The following paragraphs give the basic verification procedure for the following functions: Channels A, B and C input sensitivity, Period A, Period Averaged A, Pulse A, Time Interval A-B, Delay, Ext. Gate/Delay, and Ext.

Arming.

Specifications 1OOMHz bandwidth

0.1% basic DC accuracy 104OMHz, lo-’ 0-5O’C WMHz pulse, sine, triangle, triggered

4-i

PERFORMANCE VERIFICATION

NOTE Channel C input sensitivity verification procedure requires that the Model 7751 option be installed. TCXO accuracy verification requires that Model 7752 option be installed.

4.5.1 Channels A, B and C Input Sensitivity

The input sensitivity verification procedure is done by ap

plying an accurate sine signal to the channels A, B and C input terminals and then checking to see if the displayed value is~ stable within the required range.

NOTE Unless otherwise specified the initial set up of the Model 775 throughout the verification procedure should be the default position upon power-up. Should this set up change during one of the following verification procedures, it is imperative that the default condition is restored before the next procedure is started.

The output of the synthesized signal generator should

always be terminated, at the input terminals of the Model 775, with 500 feedthrough terminator.

1. Set the synthesized signal generator to 1OMHz and an amplitude of 25mV RMS. Apply this signal to the channel A input terminal.

2. Observe that the reading on the display is stable within the limits of lO.OOOOOOOE+6Hz *500 counts.

3. Change the signal generator settings to 1OOMHz and an amplitude to 5OmV RMS.

4. Observe that the reading on the display is stable within the limits of 100.000000E+6Hz *500 counts.

5. Change Model 775 setting to frequency B and repeat steps 1 through 4 while applying the signal to the chan-

nel B input terminal.

6. Change the Model 775 setting to frequency C.

7, Set the signal generator to 1OOMHz and an amplitude

of 25mV RMS, remove the 5OB feedthrough terminator and apply this signal to the channel C input terminal.

8. Observe that the reading on the display is stable within the limits of lO0.000000E6Hz i500 counts.

9. Change the signal generator setting to 1040MHz.

10. Observe that the reading on the display is stable within the range of 1.04000000E+9Hz f500 counts.

4.5.2 Period Measurement Accuracy Check

The period measurement verification procedure is done by applying an accurate sine signal to the channel A input terminal and then checking to see if the displayed value is within the required range.

1. Set the synthesized signal generator to lMHz and an amplitude of 1oOmV RMS. Apply this signal to the channel A input terminal.

2. Change the Model 775 setting to PERIOD A.

3. Observe that the reading on the display is stable within

the limits of LOOE-6 second +l count.

4. Change signal generator setting to 100MHz.

5. Observe that the reading on the display is stable within

the limits of O.OlE-6 second *l count.

4.5.3 Period Averaged Measurement Accuracy Check

The period averaged measurement verification procedure is done by applying an accurate sine signal to the channel A input terminal and then checking to see if the displayed value is within the required range.

1. Set the synthesized signal generator to lh4Hz and amplitude of 1OOmV RMS. Apply this signal to the chan-

nel A input terminal.

2. Change the Model 775 setting to PERIOD A.

3. Observe that the reading on the display is stable within

the limits of 1.00000000E-6 second i500 counts.

4. Change signal generator setting to 100MHz.

5. Observe that the reading on the display is stable within

the limits of 10.0000000E-9 second i500 counts.

4.5.4 Time, Interval A-B Measurement Operation Check

The time interval A-B measurement verification procedure is done by applying a square wave signal to the channels A a,nd B input terminals simultaneously, and then checking to see if the displayed value is within the required range.

1. Set the function generator to 500kHz square wave and an amplitude of 1V RMS. Apply this signal through a “T” BNC adapter to the channels A and B input terminals.

4-2

PERFORMANCE VERIFICATION

2. Change the Model 775 setting to TIME A-B, and SLOPE B setting to negative slope.

Observe that the reading on the display Is appmximate-

3. ly l.OBE-6 second.

Change the Model 775 setting to positive SLOPE B and

4. negative SLOPE A.

Observe that the reading on the display is approxlmate-

5. ly l.OOE-6 second.

4.5.5 Pulse A Measurement Operetlon Check

The pulse A measurement verification procedure is done by applying a square wave signal to the channel A input terminal and then checking to see if the displayed value is within the required

Set the function generator to 5OBkH.z square wave and

1. an amplitude of 1V RMS. Apply this signal to the channel A input terminal.

2. Change the Model 775 setting to PLS A. Observe that the reading on the display is approximate-

3. ly l.OOE-6 second.

range.

4.5.6 Delay Operation Check

The delay function verification procedure is done by applying a square wave signal, to the channels A and B input terminals simultaneously, and then checking to see of the displayed values, with and without the delay, are within the required range.

Set the function generator to Wz square wave and an

amplitude of IV RMS. Alply this signal through a “T” BNC adapter to the channels A and B input terminals.

Change the Model 775 setting to TIME A-B, and

SLOPE B setting to negative slope. Observe that the reading on the display is approximate-

ly 5OBE-3 second. Change the Model 775 MODE setting to DELAY.

Observe that the reading on the display is approximately 1.5 second.

4.5.7 External Gate Operation Check

The external gate operation verification is done by apply-

ing a Bating signal through the rear panel Input terminal and then checking to see lf the ‘reading on the display is within the requlnad range.

1. Set the synthesized signal generator to 1OMHz and an amplitude of 50mV RMS. Apply this signal to the channel A input terminal.

2. Change the Model 775 setting to frequency A and user gate mode.

3. Change function generator setting to .5Hz square wave.

4. Apply this SYNC output (‘ITL) to the rear panel EXT ARMING & GATE/DELAY input terminal.

5. Observe that the Model 775 displays 1OMHz with a resolution of nine digits.

6. Change the function generator setting to lkHz.

7. Observe that the Model 775 displays 1OMHz with a resolution of five digits.

8. Change the function generator frequency setting throughout the range of .5Hz to lOkHz and observe that the displayed resolution on the Model 775 increases when frequency setting on the function generator decreases and vice-versa.

4.5.8 Arming Operation Check

The arming operation verification is done by applying a

signal to the channel A input terminal when the Model 775 is in the hold mode; then applying an arming signal to the rear panel EXT ARMING & GATE/DELAY input terminal or depressing the RESET button to activate one measuring cycle.

1. Set the synthesized signal generator to 1OMHz and an amplitude of 50mV RMS. Apply this signal to the channel A input terminal.

2. Change the Model 775 setting to the frequency A hold mode. Note that the GATE LED does not flash, indicating that the Model 775 is in hold mode but has not received an arming signal yet.

3. Change the function generator setting to IkHz square wave and manual trigger, and apply the SYNC output (‘ITL) to the rear panel EXT ARMING & GATE/DELAY terminal.

4. Depress the MAN button on the function generator and observe that the GATE light flashed once and the Model 775 displays 10.0000000E+6Hz *500 counts.

5. Reinove the cable from the rear panel EXT ARMING & GATE/DELAY terminal leaving the above set-up as is.

6. Press once the front panel RESET button and obsenre that the display reading is cleared (0), the GATE indicator illuminates for about one second and then the following reading is displayed: 10.0000000E+6Hz +500 counts.

4-3

4.5.9 Model 7752 TCXO Accuracy Check

Model 7752 performance verification is done by using the same procedures as described above. The difference is in the resulted display, where instrument equipped with the

Model 7752 option should display a reading with a tighter tolerance. Therefore, instruments which are equipped with the Model 7752 option where specified tolerance in the above checks is 500 counts, tolerance should change to 100 counts.

4-4

SECTION 5

THEORY OF OPERATION

5.1 INTRODUCTION

This section contains an overall functional description of the Model 775 as well as detailed circuit analysis of the various sections of the instrument. Information pertalnlng to the standard IEEE interface and the Models 7751 Channel C and 7752 TCXO options are also included.

Information is arranged to provide a description of individual functional circuit blocks. As an aid to understanding, the descriptions are keyed to accompanying block diagrams and simplified schematics. Detailed schematics and componet layout drawings am located a: the end of this instruction manual.

5.2 OVERALL FUNCTIONAL DESCRIPTION

The Model 775 is a nine digit counter with six standard

measurement functions as well as one optional measure-

ment function. Model 775 utilizes a modem reciprocal

measurement technique hence increasing resolution in low

tmquency measurements; as compared to other counters which utilize the more conventional fixed gate technique. As an example, a conventional counter measuring WI2 with a gate time of one second will display a resolution

of lHz; where as the Model 775 with the same gate time,

will always display a minimum of eight digits of resolution.

A simplified block diagram of the Model 775 is shown in Figure 5-l. The heart of the Model 775 is the two counting registers: one totallzing the number of input events - the EVENT COUNTER; and one, at the same time, totalizing the number of pulses from the reference oscillator - the TIME COUNTRR. The internal microcontroller then computes the result to be displayed, using the following formula:

EVENT COUNTER

TlME COUNTER x T

where: T=the period of the reference oscillator.

The input signal is applied through the input amplifiers to switching circuits which in turn routes the signals to the correct ed, a signal from the channel C input terminal will pass through the channel C input amplifier to the internal selectors. The microcontroller, working under software control, then converts the signal into a form suitable for the display on the front panel or over the IEEE bus,

counting

circuits. If the Model 7751 is install-

5-1

THEORY OF OPERATION

5-2

Flgure 5-1. Model 775 Slmplltled Block Dlagram

THEORY OF OPERATION

5.3 ANALOG CIRCUITRY

The following paragraphs contain a description of the input circuits, measurement circuits, frequency multiplier and the power supply. These circuits may be found on schematic diagrams located at the end of this manual.

5.3.1 Input Circuits A and B

NOTE

Channels A and B are identical in terms of components and operation. Therefore, the following description, which reviews channel A circuits, applies to channel B as well. Note that letter designations for components in channel A are different for similar components in channel 8.

The signal which is applied to the channel A input signal is preconditioned in front of the amplifier circuit by means of relays and electronic components as follows:

Coupling-Coupling is controlled by a relay Kl and

capacitor Cll. When the instrument is CC coupled, Kl contacts are closed. When the instrument is AC coupled, Kl contacts are open and Cl1 blocks the DC components of the input signal:

5.3.2 Input Circuit C

The signal which is applied to the channel C input terminal is AC coupled through Cl and through the amplitude limiting network CR1 to CR6 and CRT2 and CR13 to the input of the first stage amplifier. Further protection is achieved with a fuse FL The amplifier consists of a two stage amplifier. Ql and Q2 with their associated components form the first stage, while Q3 and 44 and their associated components form the second stage. The output of the second stage amplifier (the collector of Q4) is AC coupled through C20 to a divide by 256-Ul.

5.3.3 1OMHz Standard Reference Oscillator

The reference oscillator includes a hibrid oscillator Yl, buffers U2a, b and d and a voltage regulator Ul. C2 through C4 adjust the oscillator frequency to a known reference; C4 provides a coarse adjustment and C3 provides a fine adjustment. Sl selects the signal to be applied to the Model 775 internal circuitry either an internal reference or an external standard. CR1 and CR2 protect the external input against overloads.

5.3.4 1OMHz TCXO Reference Oscillator (Option 7752)

Attenuation-Attenuation is controlled by relay K2, resistor

‘network R14 and 1215 and capacitor network Cl2 and Cl3.

When K2 is shorting between points 1 and 8 on the relay,

there is no attenuation. When K2 is shorting between

points 8 and 14 on the relay, attenuation is x10. Filtering-The low-pass filter is controlled by relay K3. Con-

tacts on K3 are normally closed thus, Cl5 is in parallel to R16. When the relay contact is open, the impedance of R16 shunted by the input capacitance of the impedance converter, act as a low-pass filter.

Input Protection-Front panel conditioning is capable of handling signals within the specified dynamic range of the Model 775. Protection <If the input circuit from over-voltage signals (up to the specified limits) are accomplished by R17, CR2, 3 and CRZ.1.

Amplifier-The amplifier consists of an impedance converter formed by QZO, an amplifier formed by and U34a, and their associated components. The trigger level is controlled by Q22 via L15 and R33. The slope that the input signal trisers on is controlled by an exclusive OR circuit-U35.

and

a Schmidt trigger which is formed by U34b

Q21

and Q22

The TCXO reference oscillator circuit consists of a hybrid oscillator Yl, buffers U2a, band d and a voltage regulator Ul U2d is an output buffer which connects the internal

1OMHz signal to a rear panel BNC terminal.

5.3.5 100MHz Multiplier

The 1OMH.z reference oscillator is multiplied internally to generate a stable 1OOMHz signal which is related both in phase and accuracy to the 1OMHz reference oscillator. The

1OMHz signal from the reference oscillator is coupled to the multiplier via C49. U50a converts the TTL signal coming from the oscillator to a sine wave which is then fed

to Q37.437 amplifies the 1OMHz signal and produces two

1OMHz signals with a phase difference of 1804 CR16 and

CR17 act as full wave rectifiers, thus creating a 20MHz signal. The 20MHz signal is fed via C58 to a tuned circuit where LA and C62 are tuned for 20MHz. The x5 multiplier consists of U51a and U51b which are tuned by the tank circuits I.5C67 and L&C70 to the fifth harmonic of the

20MHz signal.

5-3

TIIEONY OF OPERATION

The lOOMFIr signal is finally coupled through 0’2 to the

lOOMHa buffer Q38 and its associated components.

5.3.5 Measurement Section

The measurement section is a block which controls various switching, routes the internal signals to the correct ports. It also controls the sequence of the gate and resets and synchronizes the time and the event counters for the microcontroller. Figures 5-2 to 5-7 show the routes for the input s&nal and the reference signal in every measurement function. The following is a brief explanation of the various

segments in the measurement section. Control-The control circuit consists of U26, U28 and U30.

Information from the microcontroller is sent in a serial form to control the ICs which in turn convert the serial information to a parallel format. The parallel outputs of these ICs are being used to control the D to A converters and the signal routes as described previously.

Trigger Level--The trigger level circuit comprises U31, U32, U33, UW, U29 and their associated components. Binary data which is received from the control circuit is converted by U31 and UW to a known DC voltage with U32 and U29 respectively. U33 is a +5V voltage reference with very good stability. R6 adjusts the full scale voltage of the D to A converters.

Main Gate-The main gate of the Model 775 consists on

U42c. Signals from the synchronizer or the time detector are applied to one input of this reference signal is applied to the second input resulting

at the output of the gate.a 1OOMHz burst of pulses.

Clock Divider-The burst of pulses with a frequency of

1OOMHz divided by two by U41b and applied to the ECL to the TTL through U43a to the dividers chain.

Signal Divider-The signal coming from the synchronizer

circuit is divided by two using a D flip-flop U4Ob and ap

plied to the ECL to the TTL converter which in turn out-

puts a TTL signal through U49b to the divider chain.

Signal Identifier-The signal identifier comprises U4la, Q28

and 429 and their associated components. A signal when

present at the appropriate input terminal, is applied to the CLK input of U4la, converted to a Tl’L level signal with Q28 and Q29 and then fed to one of the microcontroller ports via U49a. This port will be used to flag the presence of a signal at the input terminals. This signal is also used as the arming signal of the counter.

Gate Identifier-The gate identifier informs the micmcontroller of theistate of the main gate. The gate identifier circuit also serves as a time stretcher of gate signals with very small periods. The gate identifier consists of U43b, 433, Cl0 and is buffered by U43d and U43c.

converter

which in turn outputs a TIL signal

gate

and the ICOMHz

Signal Selector-The signal selector circuit comprises U3% U38a and U38b. One of Sig 0 through Sig 3 are selected to be transmitted to the time detect, signal identifier or the synchronizer.

Time Detect-The time detect circuit consists of a dual D flip-flop U39 and a gate L&Id. U39a receives the start signal

and U39b (elk in) receives a stop signal. Following a reset signal at the reset input of U39, U38d outputs a single negative going pulse with a duration which is equal to the

time interval between the start and the stop signals,

regardless if the start and the stop signals are repetitive.

Synchronizer-The synchronizer consists of a D flip-flop LJ40a and a gate U38c and their associated components. A gate signal is applied from fhe microcontroller to the D input of U4Oa and the measured signal is coupled to the CLK input on the same IC. After a reset cycle, and assum-

ing that a signal is present at the appropriate input ter-

,minal, the output of U4Oa will generate a pulse with an

approximate width of the original gate signal from the

microcontroller, but with a new adjusted width which is

equal to an integer number of periods of the signal being

measured. This pulse will be used as the main gating

signal throughout the instrument. Gates U42a. U42b and

U42d control the routing of the synchronized gate and the

trme interval pulses to the main gate of the Model

775442c.

Event Counter-The event counter counts the number of pulses or events which occur at the input terminal. The event counter comprises a high speed divider chain which

is formed bythe signal divider circuit in combination with U44 and U45 and a low speed counter Ul2.

Time Counter-The time counter counts the number of pulses from the reference oscillator. The time counter corn. prises a high speed divider chain which is formed by the clock divider circuit in combination with U46, U47a, U48

.and a low speed counter Ul3.

5.3.7 For the following discussion, refer to the power supply

schematic at the end of the manual. The power supply is made up of’s line fuse, power on-off switch, line voltage selection switch, power transformer, two bridge rectifiers, two regulators and a 5V regulator which is formed by U54, Q40, 441 and 439 and their associated components.

Fuse Fl is the LINE FUSE which is accessible on the rear

panel. 52 is the LINE VOLTAGE SELECT switch which is accessible on the rear panel to select ll5V or 230V operation and Sl is the power on-off switch.

Pow&r Supply

5-4

THEORY OF OPEAATIOh

CR18 is used as a full wave rectifier to provide a sufficient

ply. This reference is then buffered by U54 amplifier and DC voltage for the +l2V and XV regulators U52 and U53 applied through Q41 to the series regulator Q40. Q40 is respectively. mounted on the rear panel to absorb the heat generated

by the power transistor. Q39 and Rl23 form a protection circuit against accidental shorts or overload.

LJ54 receives a reference voltage of 5V from the ‘l2V sup-

5-5

THEORY OF OPERATION

5-6

Figure 5-2. Frequency A Measurement Block Diagram

THEORY OF OPERATION

FIgwe 5-3. Frequency B Measurement Block Dlagrem

6-7

THEORY OF OPERATION

6-6

Figure 5-4. Frequency C Measurement Block Diagram

THEORY OF OPERATION

I III” I

Figure 5-5. Period A Measurement Block Diagram

5-9

THEORY OF OPERATION

5-10

Figure 5-6. Time Interval A-B Measurement Block Diagram

THEORY OF OPERATION

t t-

Y-2

Flgure 5-7. Pulse Width Measurement Block Diagram

5-11

THEORY OF OPERATION

5.12

Figure 5-6. Microcomputer Block Qiagram

THEORY OF OPERATION

5.4 DIGITAL CIRCUITRY

Model 775 operation is supervised by the internal microcomputer. Through the MCU, the counter measurement process, the front panel switchin , f display, and IEEE

operation are all performed under so tware control. This section briefly describes the operation of the various sections of the microcomputer and associated digital circuitry. A simplified block diagram is included for user reference; for more complete circuit details refer to the digital schematics at the end of this manual.

5.4.1 Microcomputer Block Diagram

A block diagram of the Model 775 microcomputer is shown in Figure 5-8. Circuit operation centers around the microcontroller unit (MCU), U6. The 8031 is an B-bit microcontroller capable of directly addressing up to 64K bytes of program memory (ROM) and up to another 64K bytes of data memory (RAM). The microcontroller works with a 1OMHz clock which is divided internally to provide bus operation of about lh4Hz.

5.4.2 Memory Mapping

The 8031 microcontroller is capable of directly addressing two banks of 64K (65,536) byte memory. One bank of memory is the program memory and the second memory bank is the data memory. The selection of the banks is

done internally by the MCU. Although the MCU has this

large addressing capability, only a portion of the possible

memory space is actually needed.

The Model 775 uses a total of 8K of program memory

stored in the 2764 EPROM U9, and a total of lK of data memory is stored in UlO and Ull. The 8031 MCU uses a memory-mapped I/O scheme, additional memory locations must be allocated for the various I/O functions. All the memory-mapped Ii0 functions are in the data memory space. Table 5-l lists the memory locations for the various memory elements.

Because of a partial decoding scheme used in this instru-

ment, for some memory elements, a larger memory slot

is allocated than the actual memory needed.

Software for the MCU is contained in an EPROM (Erasable Programmable Read-Only Memory). U9 is a 2764 EPROM containing 8K bytes of software. Temporary storage is provided by UlO and Ull RAMS which can store up to 1024

byies of information.

interfacing between the MCU and the IEEE bus is performed by the dedicated IEEE-488 bus interface IC, UZO.

This IC performs many bus functions automatically to

minimize MCU overhead. Buffering between the 8291 IC and the IEEE bus lines is done with the bus drivers U21 and U22.

interfacing between the MCU to the keyboard and the

display is performed by the Keyboard/Display interface

IC-U5.

Table 5-l. Model 775 Memory Mapping

Selected

Device

RAMS UlO, Ull) Display interface (U5) IEEE (U20) Address Switch (U23) Counters (VU, Ul3)

Allocated Memorv

$lOOO-$3FFF $4OLlO-$4OFF !§4300-!§4FFF

5.4.3 Address Decoding

The MCU has a total of 16 address lines which are used

to locate a specific memory slot. The LOW address line (A0 to A7) are multiplexed on the address/data bus, and the ALE (address latch enable) signal is used to separate the LOW address from the address/data bus which is done by U7 address latch. Since no memory or interface element can fully decode ‘Iddress locations, additional address decoding must bc used.

U8 is l-of-8 decoder. The dewder is enabled when address lines Al4 is HIGH and A.12 is LOW. Once the decoder is selected the decoding is done by addressing line A8, A9 and AlO. When address line A12 is HIGH the RAMS are selected.

513

THEORY OF OPERATION

5.4.4 Keyboard/Display interface

The Keyboard/Display Interface IC LJ5 is used to control the front panel display and to determine which one of the buttons was pushed.

5.4.5 IEEE interface

The Model 775 has a built in IEEE-488 interface that allows the instrument to be controlled through the system controller. Commands may be given over the bus and data may be requested from the instrument as well.

The IEEE interface is made up of UZO, a 8291 GPIA (General Purpose Interface Adapter), and U21 and U22, which are interface bus drivers. On the MCU side of the GPIA, data transmission is handled much like any other bus transaction. The MCU accesses the GPIA through the usual DO through D7 data lines. Address decoding for the

internal 16 registers (8 read and 8 write) is provided by the CS, WR, RD and AO, Al A2 terminals.

The output of the 8291 IC is standard IEEE format; the eight data lines (DIOl through DI08) the three handshake lines (DAV, NDAC, NRFD), and the five management lines (ATN, REN, IFC, SRQ, EOI), are all active low with approximately zero volts representing a logic one. The two IEEE bus drivers, U21 and U22 are necessary to bring the drive capability of the interface up to the normal IEEE maximum I5 devices.

The GPIA simplifies MCU interfacing to the IEEE bus because many control sequences take place automatically. For example, when a write is done to the data output register, the handshake sequence is automatically performed at the proper time. Without the GPIA chip, complictaed MCUiroutines would be required to accomplish control sequence that are performed automatically.

514

SECTION 6

MAINTENANCE

6.1 INTRODUCTION

This section contains informaton necessary to maintain, calibrate and troubleshoot the Model 775, Model 7751 Channel C option and Model 7752 TCXO option. Fuse replacement procedures, line voltage selection and Model

7751 and Model 7752 installation procedures are also included.

WARNING The procedures described in this section are for use only by quellfled service personnel. Do not prform these procedures unless quslifisd to do so. Many of the steps covered In this section may expose the lndlvldusl lo potenttally lethal voltages that could result in personal Injury or death If normal safety precautions am not observed.

0.2 LINE VOLTAGE SELECTION

The Model 775 may be operated from either ll5V or 23OV

nominal 50-6OHz power sources. A special transformer may be installed for lO0V and 2wV ranges. The instrument was shipped from the factory set for the operating voltage marked on the rear panel immediately above the power line receptacle. To change the line votlage, proceed as follows:

CAUTION The correct fuse type must be used to maintain proper instrument protection.

3. Mark the selected voltage on the rear panel with a water soluable marking pen for future reference.

6.3 FUSE REPLACEMENT

The Model 775 has a line fuse to protect the instrument from excessive current. This fuse may be replaced by using the procedure described in the following:

WARNING

Disconnect the Instrument from the power line and from other equipment before replacing the fuse.

1. Place the end of a flat-blade screwdriver into the slot in the LINE FUSE holder on the rear panel. Push in and rotate the fuse carrier one quarter turn counterclockwise. Release pressure on the holder and its internal spring will push the fuse and the carrier out of the holder.

2. Remove the fuse and replace it with the proper type using Table 6-l as a guide.

WARNING

Disconnect the Model 775 from the power cord and all other WUIESS before changing the line WItage sattlng.

selection switch in the desired position. The voltage selection switch is located above the Dower line receptacle.

2. Install a power line fuse consistent with the operating voltage (see paragraph 6.3 step 1).

CAUTION 00 not use a fuse with a rating higher than specified or Instrument damage may occur. If

the instrument persistently blows fuses, a pro-

blem may exist within the instrument. If so, the problem must be rectified before continuing ooeration.

. 1. Using a flat-blade -driver, place the line voltage

Table 6-1. Line Fuse Selection

6-1

6.4 USING AN EXTERNAL TIMEBASE

The Model 775A may use an external 1OMHz time base with the standard 5ppm time base of the 7752 TCXO time base. The following steps are required to use an external timebase.

1. Remove the top cover of the instrument as described in the disassembly instructions in paragraph 6.9

2. For the standard 5ppm time base locate switch Sl on the timebase board and slide it to the EXT position. See Figure 6-L4 for the location of Sl. The EXT position is with the switch towards the front of the Model 775.A

3. For the TCXO time base, locate switch Sl and slide it

to the EXIT position. The EXT position is with the

switch towards the top of the Model 775A.

4. Reinstall the top cover as described in paragraph 6.9.

5. Apply the TTL level (0 to +5V) 1OMHz to the CLOCK IN/OUT BNC terminal on the rear panel. See Figure 2.2 for the location of this terminal.

CAUTION Do not exceed the TTL voltage levels or damage to the Model 775 or the external source may oc-

cur. The EXT CLOCK input impedance of the

Model 776 is nominally 2000, be sum to uss the

appropriate impedance mstching devices to ensure that ringing and cable reflectlons are

minimized. Severe rlnglng and waveform defor-

matlon may cause false or improper clock operatlon.

*”

6-2

Figure 6-1A. Model 775A Standard 5 ppln Time Base

Figure 6-1B. Model 775A TCXO Time Base

MAINTENANCE

cL, 6.5 MODEL 7751 CHANNEL C OPTION

INSTALLATION

The Model 7751 Channel C option expands the capability

of the Model 775 by allowing it to measure frequencies up to l.OGHz. If purchased with the Model 775, the Model 7751 will be factory installed; however, removal for service will require installation as follows:

1. Remove the top cover of the instrument as described in the disassembly instructions in paragraph 6.9.

WARNING Disconnect the line cord and test leads from the instrument before removing the top cover.

2. Plug the Model 7751 into the comb type connector which is located in the front section of the instrument. The Model 7751 PC board should slide easily to its ween the two card guides.

Locate the shielded cable which is connected on one side to the channel C input terminal. The other side of this cable is soldered to one card guide to prevent this end

from rattling inside the instrument and causing shorts. Unsolder the shielded cable from the guide and solder the prestripped cable as illustrated in Figure 6-2.

Solder both sides of the PC board,to the card guides.

4. This will secure the Model 7751 to its place and will pre-

t Model 7751 from loosening during transit.

5. Replace the top cover.

6. Turn on the power and wait until the power up procedure is complete. Then depress the FREQ C button and observe that the FREQ C light turns on. The instrument is now ready to take measurements of frequencies up to l.OGHz.

1 _

place

bet-

Figure 6-2. Model 7751 Installation

6-3

MAINTENANCE

6.6 MODEL 7752 TCXO OPTION INSTALLATION

The Model 7752 TCXO option increases the accuracy of the Model 775 by improving the accuracy and the stability of the reference oscillator. If purchased with the Model 775, the Model 7752 will be factory installed; however, removal for service will require installation as follows:

1. Remove the top cover of the instrument as described

in the disassembly instructions in paragraph 6.9.

WARNING

Disconnect the line cord and test leads from the instrument before removing the top cover.

2. The standard oscillator circuit is built on a separate PC

board and is located in the back of the Model 775 near

the transformer. Locate the oscillator circuit and remove the solder joint that secures the board to the guide.

3. Remove the oscillator board by pulling the board up un-

til it disconnects from the comb type connector.

4. Disconnect the shielded cable, coming from the oscillator board, from the rear panel BNC connector.

5. Slide the Model 7752 option along the card guide and push the card down until it locks into place as shown in Figure 6d3.

CAUTION Make sure that Model 7752 is plugged correctly into to the main connector. No pin should be lefl free.

Solder the loose end of the shielded cable to the rear

6. panel BNC terminal. The inner wire of the cable should be soldered to the center conductor on the BNC where as the shield part of the cable should be soldered to the shell of the same connector.

7, Solder the side of the PC board to the card guide. This

will secure the Model 7752 to its place and will prevent the Model 7752 from loosening during transit.

8. Replace the top cover.

9. Mark the correct option installation on the rear panel with a water soluable marking pen for future reference.

6-4

Figure 6-3. Model 7752 Installation

MAINTENANCE

6.7 CALIBRATION

6.7.1 Environmental Condltlons

Adjustments should be performed under laboratory conditions having an ambient temperature of 24 @‘C and a relative humidity of less than 70%. If the instrument has been subjected to conditions outside these ranges, allow at least one additional hour for the instrument to stabilize before beginning the adjustment procedure.

6.7.2 Warm-Up Perlod

Most equipment is subject to at least a small amount of

drift when it is first turned on. To ensure long-term calibration accuracy, turn on the power to the Model 775 and allow it to warm-up for at least two hours before beginrung the adjustment procedure.

6.7.3 Recommended Test Equlpment

Recommended test equipment for calibration is listed in Table 6-2. Test instruments other than those listed may be used only lf their specifications equal or exceed the required characteristics.

NOTE

In order to perform the following calibration procedures, the top shield must be removed to gain access to various components. To do so, remove the three screws that secure the shield to the

board. Replace the shield after adjustments are

complete.

WARNING

Take gpeclal cara to prevent contact with live circuits or power line area which could cause electrical shock resulting in serious injury or death.

Use an isolated tool when making adjustments. Use plastic or nylon screwdriver when adjusting

the time base trimmer.

Refer to Figure 6-4 and the component layout in Section 7 when necessary for determining adjustment points.

Follow the procedure in the sequence indicated since some

of the adjustments are interrelated and dependent on the

proceeding steps.

Verify that the Model 775 is functioning according to the performance checks. Make sure that all results are within or close to the range of the required specifications, otherwise refer to the troubleshooting information given at the end of this section.

6.7.4 Callbratlon Procedure

All adjustments are performed with the POWER switch ON. The top cover should be removed to allow access to test points and adjustments. Between adjustments, always leave top cover on the unit to keep maintain temperature.

Table 6-2. Recommended Test Equipment For Calibration

Recommended

Inahument

Oscilloscope Tektronics 465 Multimeter

Function Generator HF33l7A 13MHz ~pulse, sine, triangle, triggered l0MI-h Standard Oscilloquartz 2200 IxE-lo/day, 5xE-10 0-50°C

Model Keithley 175 .l% basic DC accuracy

Perform the following adjustment procedure. If an adjustment can not be made to obtain a specific reading, refer to the troubleshooting information at the end of this section.

NOTE If not otherwise specified, perform all adjustments on the Model 775 in the power up default position.

Specifications 1OOMHz bandwidth

6-5

MAINTENANCE

6-6

I I

Figure 6-4. Model 775 Calibration Adjustments

MAINTENANCE

6.7.5 Multiplier Adjustment

1. Connect the probe to the collector of 438. Use a short ground clip. Refer to Table 6-2 for recommended test equipment.

2. Set up the oscilloscope and adjust C67 and C70 to get a maximum amplitude of lOOMI& slnusodial signal. Note that the signai may appear modulated and

distorted. This has no effect on the normal operation

of the Model 775. Alter adjustments between C67 and

C70 untiI a peak to peak amplitude of about 1.5V is

reached.

6.7.6 Trigger Level Adjustment

1. Set the multimeter to DC voltage measurement. Refer to Table 6-2 for recommended test equipment.

2. Connect the multimeter probes between pin 15 of U27 and case ground.

3. Adjust R6 to give a voltage reading of 2.55V ilOmV on the DMM.

6.7.7 Channels A and 6 Sensitivity Adjustment

1. Set the function generator to lkHz sine wave and 40dB attenuation. Refer to Table 6-2 for recommended test equipment.

2. Set the multimeter to ACV and 200mV range.

3. Connect the function generator output to the DMM and adjust function generator amplitude control to give a reading of l5mV on the DMM.

4. Connect the function generator output to the channel A input terminal.

5. Connect the oscilloscope probe to pin 3 of U38.

6. Set up the oscilloscope and adjust R23 to display a rectangular waveform of IkHz with a duty cycle of 50%

*lO%.

7. Change the Model 775 setting to FREQ B.

8. Connect the function generator to the channel B input terminal.

9. Set up the oscilloscope and adjust R50 to display a rectangular waveform of IkHz with a duty cycle of 50%

*lO%.

6.7.6 Inputs A and B Attenuator Compensation

1. Set the function generator to give 1OkHz rectangular waveform with an amplitude of 1OV peak to peak. Refer to Table 6-2 for recommended test equipment.

2. Change the Model 775 setting to AC coupling and x10 attenuation on both channels A and B.

3. Connect the function generator output to channel A in-

put terminal

4. Connect the oscilloscope probe to the junction of R20 and R21.

5. Set up the oscilloscope and select Cl3 to give a rising edge with a minimum overshoot or undershoot. Cl.3 should be in the range of 15pF to 20pF.

6. Change 775 setting to FREQ B and connect function generator to channel B input terminal.

7. Connect the oscilloscope to the junction of R47 and R48.

8. Set oscilloscope and select C33 to give a rising edge with a minimum overshoot and undershoot. C33 should be in the range of l5pF to 20pE

6.7.9 Time Base Adjustment (Standard 5 PPM

Time Base)

1. Allow the Model 775 to warm up for at least two hours with covers installed at an ambient temperature of 25OC

*2”C. Refer to Table 6-2 for recommended test

equipment.

2. Connect 1OMHz standard output to the channel A input terminal.

3. Set C3 to about mid range (5 turns trimmer capacitor).

4. Adjust C4 to give a reading of 10.0000000 +200 counts

on the display. If proper adjustment cannot be obtained, adjust C2 to bring C4 within range. (C2 should

be in the range of 8pF to I2pF).

5. Adjust C3 to give a reading of lO.O~OOO,OO +50 counts

on the display.

6. Allow an additional warm-up time of approximately 30

minutes. Repeat step 5 if necessary.

6.7.10 Time Base Adjustment (Optional 1 PPM Time Base)

1. Allow the Model 775 to

covers instaIled at an ambient temperahire of 73 (I ,L’C. Refer to Table 6-2 for recommended te>t ~~~Iuipment.

2. Connect 1OMHz standard output to the channel A in-

put terminal.

3. Adjust the trimmer on top of the TCXO case using with a very narrow plastic screwdriver to give a reading of

10.0000000 *lo counts on the display.

4. Allow an additional warm-up time of approximatly 30 minutes, Repeat step 3 if necessary.

warm up at kast tic> 11~au1.i \vith

6-7

MAINTENANCE

6.6 SPECIAL HANDLING OF STATIC SENSITIVE DEVICES

MOS devices are designed to operate at a very high impedance levels for low power consumption. As a result, any normal static charge that builds up on,your person or clothing may be sufficient to destroy these devices if they are not handled properly. Table 6-3 lists the static sensitive devices in the Model 775. When handling these devices, use precautions which are described in the following table to avoid damaging them.

Table 6-3. Static Sensitive Device

Schematic

Designation

Ul3 u20 U25 U26 U27 U28 u30 u31

1. The ICs listed in Table 6-3 should be transported and handled only in containers specially designed to prevent static build-up. Typically, these parts will be received in static-protected containers of plastic or foam. Keep these devices io their original containers until ready for installation.

2. Remove the devices from the protective containers only at a properly grounded work station. Also ground yourself with a suitable wrist strap.

Keithley

Part Number

KO500-2141

LSI-52 KO550-0010 KLI550-VI10 KO500-2130

IC-251

IC-251 K!3560-0070

K-2

X-251 K!3560-0070

3. Remove the device only by the body; do not touch the pins.

4. printed circuit board into which the deivce is to be inserted must also be grounded to the bench or table.

5. Use only an anti-static type solder sucker.

6. Use only ,gmunded soldering irons.

7. Once the device is installed on the PC board, the device is normally adequately protected, and normal handling may resume.

6.9 DISASSEMBLY INSTRUCTIONS

If it is necessary to troubleshoot or replace a component, use the following disassembly procedure to remove the top cover and refer to Figure 6-5.

1. Remove the two screws that secure the top cover to the rear panel.

2. Grasp the top cover at the rear and carefully lift if off the instrument. When the tabs at the front of the cover clear the front panel, the cover may be pulled completely clear.

3. When replacing the top cover, reverse the above procedure; be sure to install the tabs at the front panel before completely installing the cover.

NOTE

The Model 775 covers are coated with shielding

material to suppress RFI and EM1 noises which are generated by the internal circuits. When replacing the top ,cover on the Model 775, make sure that

the springs that are mounted on both sides of the

rear panel make contact with the internal shield of the top cover. If the springs are loose or are not

making contact, push the loose ends toward tne

outside.

TOP COVER

30540

MAINTENANCE

ENC CONNECTOR

K1100~1010 or

DISPLAY BOARD 11)

‘USHEUTTON

TILT SAIL

NOT SHOWNI

30544

BNC CONNECT0

JSHBUTTONS: ICAL, RESET 228-317-4 IODE. TIME, PERIOD FRE(1: 228-317-5 OVERLAY 775-303 HAN A, CHAN S. CHAN C: 228-317-6

FRONT PANEL

GROUND CLIPS 12

MODEL 7752

TCXO OPTION

Figure 6-5. Model 775 Exploded View

6-9

MAINTENANCE

6.10 TROUBLESHOOTIMG

The troubleshooting instructions contained in this section are intended for qualified personnel having a basic understanding of analog and digital circuitry. The individual should also be experienced at using typical test equipment as well as ordinary troubleshooting procedures. The information presented here has been written to assist in isolating a defective circuit or circuit section; isolation of the specified component is left to the technician.

6.10.1 Recommended Test Equipment

The success or failure in troubleshooting a complex piece of equipment like the Model 775 depends not only on the skill of the technician, but also relies heavily on accurate, reliable test equipment. Table 6-2 lists the recommended test equipment for a complete troubleshooting and adjustment of the Model 775. However, it is also possible to troubleshoot the Model 775 with the minimum equipment which is listed in Table 6-4. Other equipment such as a logic analyser, an in-circuit emulator etc, could also be helpful in difficult situation.

6.10.2 Power-Up Self Diagnostics

An advanced feature of the Model 775 is its self diagnosing capabilities. Upon power-up the Model 775 performs a set of tests which is described in paragraph 2.4. If the Model 775 locks up due to ROM or RAM fail, there is lit-

tle point in attempting to troubleshoot micmonhdler

The power-up diagnostic test may be run either upon power-up or through the’IEEE-466 mterface bus. The procedure to run a self diagnostic program thrnugh the bus

is described ,in detail in Section 3.

6.10.3

It is higmy recommended that the fhst step in

troubleshooting the Mode1 775, as well as any

equipment, would be to check the power supply. If the various supply voltages within the instrument are not within the required limits, troubleshooting the remduring circuits can be very difficult. Table checks that can be made to the power su Model 775. In addition to the normal vo tage checks, it is also a good idea to check the various supplies with an oscilloscope to make sure no noise or ringing is present.

In case of a “dead short” between one of the supplies to the common ground, it would be best to disconnect the entire supply section from the remaining circuitry and then identify if the problem is in the power supply or in the remaining circuitry. Model 775 is equipped with points which are located on the bottom side of the main PC board To access these points, remove the bottom cover and the solder from the quick-disconnect points.

Power Supply Check

circuit Is operating pmperly.

elsewhm until the

~imihu

6-5

shows the

plies within the

WIOUS

‘6-10

Recommended

Instrument Oscilloscope

Multimeter Keithley 175 Function Generator HP-33l2A

Model Specifications: Tektronics 465 1OOMHz bandwidth

.l% basic DC accuracy l3MHz pulse, sine, triangle, triggered

MAINTENANCE

6.10.4 Reference Oscillator and Clock Checks

The most important section to be verified after the power supply checks, is the reference oscillator. The reference oscillator supplies different clock signals to the various sections of the Model 775. Without these clock signals, the microcomputer would not start to generate the control lines thus, making it impossible to troubleshoot the remaining circuitry.

Table 6-6 shows the various checks that can be made to

verify the operation of the clocks and the reference oscillator.

6.10.5 Digital Circuitry and Display Checks

Problems with the digital and display circuitry could cause

erratic operation or false readings on the display. Check the various components associated with the digital circuitry, including the IEEE-488 interface, using the information in Table 6-7.

6.10.6 Signal Conditioning and Input Circuit

Checks

Problems in these circuits could generate false results on the Model 775. Tables 6-8 and 6-9 list checks to be made

on the signal conditioning and the input circuits respectively.

6.10.7 Multiplier Clrcult Checks

Problems with the multiplier circuit will definitely cause false results on the Model 775 or may cause no result at all. Problems in the multiplier circuit may be identified using Table 6-10.

6.10.6 Trigger Level Checks

The trigger level circuits control the threshold point where

the input circuit triggers. The Model 775 may not trigger at all on a signal that appears to be within the specified limits. Problems in the trigger circuit may be located us-

ing the checks given in Table 6-11.

6.10.9 Measurement Section Checks

The measurement section circuitry is mainly used as a digital control to the analog signals within the Model 775. Due to high speed signals, it was necessary to implement ECL technology. It is recommended that the checks in Table 6-12, using an oscilloscope, be made with a special high frequency probe that has a very short grounding clip.

Table 6-5. Power Supply Checks

Required Condition Set to 1l5V or 230V

Continuity Plugged into live receptacle; power on.

+l2v f5% +l5V minimum

-lzv *15%

-l5V minimum +5v *5% +7V minimum +5v *5%

Remarks See paragraph 6.2.

Remove fuse to check.

c12V on U52 output

Positive output of CR18

-12V on IJ53 output Negative output of CR18 Collector of 440 Positive output of CR19 Input 3 to U54

6-11

MAINTENANCE

‘

Step 1 Item/Component 1 Required Condition

1 1OMHz Reference

2 1OMHz Reference 3 Multiplier Clock 4 Microprocessor Clock

5 Microprocessor Timer

6 Keyboard and Display

7 IEEE Interface Clock

I-----

km/Component

SteJ

1 2

?.eset Input

4LE Line FSEN Line wlses iiD WR Lines

Address/Data Bus

3erial Data In

Serial to Parallel Converters Clocks

Keyboard Interrupt Line

LEDs Sink Lines 0 to +4V variable pulses

Table 6-6. Reference Oscillator and Clock Checks

Control Clock

1 Test FoiitlRemarks

Turn on power. 0 to +4V 1OMHz square

0 to +4V 1OMH.z square wave Pin 3 on U2a on TCXO

-0.2V to +O.ZV 1OMHz Pin 2 on U50a. Signal may

square wave

0 to +4V 1OMHz square wave Pin 19 0 to +4V 5kHz square wave Pin 14 on U6 0 to +4V 1.25MHz Pin 3 on U5 square wave 0 to +4V 5MHz square wave

Pin 6 on U2d on standard oscillator board.

oscillator board. appear very noisy.

Pin 3 on U20

Table 6-7. Digital Circuitry and Display Checks

Required Condition

Turn on power.

Turn off instrument then back on.

0 to +4V 168nsec pulses Pin 30 on U6 0 to +4V 276nsec negative going

0 to +4V 480nsec negative going pulses 0 to +4V variable pulse train

Depress and hold the LEVEL A button during the next two tests. 0 to +4V variable pulse train

0 to +4V burst of pulse train

Depress e&h one of the buttons, in turn, on the front panel throughout the next 0 to c4V variable negative going pulse.

test.

- --

Test Point/Remarks

Some tests here

to digital problems. Pin 9 about .lsec and then goes high.

Pin 29

Pins 16 and 17 on U6 Pins 21 thru 28 and Pins 32

thru 39 on U6

This will generate serial data

on the RXD lines. Pin 2 of U30 Pin 2 of U28 Pin 2 of U26 Pin 2 of U25

Pin 3 of LJ30 Pin 3 of U28 Pin 3 of U26 Pin 3 of U25

This test will check all buttons

on the front panel as well as the interrupt line. Pin 4 of US

Pins 10 to 16 on U2 and Collector of Q16

U6 stays low for

on U6

could fail due

6-12

Table 6-6. Signal Condltloning Checks

MAINTENANCE

Item/Component

Turn .on power. The following tests are per-

Input conditioning signals: DC AC Xl x10 Filter On Filter Off Negative Slope Positive Slope

TTL High Level Pin 4 Pin 6 TTL Low Level TTL Low Level TTL High Level Pin 14 Pin 12 TTL Low Level Pin 13 Pin 5 TTL High Level Pin 13 Pin 5 TTL Low Level Pin 11 Pin 7 TTL High Level

Table 6-Q. Input Circuit Checks

Item/Component

Channel A Front End Input Amplifier A Gab

Channel B Front End Input Amplifier B Gair

Required Condition Test Point/Remarks

formed on U25 Channel A Channel B

Pin 4 Pin 14

Pin 11

Required Condition Turn on power.

lMHz .lVp-p sine

+3.2 to +4.2V pulses with 50% duty cycle Depress FREQ button FREQ B light should be

on.

lMHz .lVp-p sine

+3.2 to +4.2V lMHz pulses with 50% duty

Test Point/Remarks Apply lMHz .lVp-p

sine to Channel A input BNC. Base of 421 Pin 3 of U34b

Apply lIvlHz .lVp-p sine to Channel B input BNC. Base of Q25 Pin 3 of U36

Pin 6 Pin 12

Pin 7

Table 6-10. Multlpller Circuit Checks

Step Item/Component

1 2 TTL to Sine Converter 1OMHz sine wave 2V p-p

3 x2 Multiplier 4 x5 Multiplier

Required Condition

Turn on power.

20MHz sine wave 1V p-p Pin 8 of U50b 1OOMHz sine wave 1V p-p Collector of Q38

Test Point/Remarks Signal may appear noisy

in the following tests. Pin 14 of U50a

6-13

MAINTENANCE

Table 6-11. ‘Rigger Level Circuit Checks

I Item/Component

D to A Reference

Channel A Posit Trigger Level Channel B Positive Trigger Level

Channel A Negative -2.55V *ZOmV Pin 10 of U29A Trigger Level Channel B Negative Trigger Level

btep Function

2 FREQ A 3 FREQ B

4 FREQ C

5 PERIOD A 6 PERIOD AVG A 7 TIME A-B 8 TIME PLS A

9 Signal Selector 10 Time Detect 11 Synchronizer

12 Signal Divider 13 Signal Identifier

14 Gate Identifier

15 Main Gate 16 / Clock Divider

Required Condition

Test PointRemarks

Turn on power.

+2.55V i2OmV

Pin 15 of IJZ7 and Pin 15

of u31 Change front panel trigger level setting for Channels A and B to

+2.55V.

ive +2.55V t2OmV

+2.55V +ZOmV

Pin 10 of U29b Pin 12 of U32a

Change front panel trigger level setting for Channels A and B to

-2.55V.

-2.55V +ZOmV

Pin 12 of U32a

Table 6-12. Measuring Section Circuit Checks

Required Condition

Turn on power. Pin4 Pin5 Pin6 Pin7 Pin11 Pinl2

1 It 0 1 :110 1 1

: E

10 0 111 0 1 110 1 1 0

10 11 0 1

11010 1 Change panel setting to FREQ A and lsec gate time. Apply lMHz 1V p-p sine to Channel A BNC.

+3.2V to +42V lMHz pulse. Pin 15 of U37d

Don’t care. Pin 9 of U38d

+3.2V to +4.2V lMHz burst. Pin 14 of U38c Width of burst is approx. lsec. TTL 500KHz burst. Width of burst Pin 6 of U49b about lsec. TTL low level during measurement cycle, lTL high for about lmsec after each cycle. lTL low level when gate is open, TTL high for about 300msec after

gate closure.

t3.2V to +4.2V 1OOMHz burst.

Width of burst is about lsec.

TTL 50MHz burst. Width of burst

1 approx lsec.

Test Point/Remarks The next six tests would be performed

on U28.

Possible with Model 7751

Pin 3 of U49a

Pin 8 of U43c

Pin 14 of U42c Pin 3 of U43a

614

SECTION 7

REPLACEABLE PARTS

7.1 INTRODUCTION

This section contains replacement parts information, component location drawings and schematic diagrams for the Model 775.

7.2 PARTS LIST

Parts for each board are listed alphanumerically in order of their circuit designations. When ordering a part, indicate the printed circuit board that the part is located on as well as the part number. Table 7-1 contains parts list informa-

tion for the mother board. Table 7-2 contains a parts list for the display board. Table 7-3 contains a mechanical parts list for the Model 775.

7.3 ORDERING INFORMATION

To place an order, or to obtain information concerning

replacement parts, contact your Keithley representative or

the factory. See inside front cover for addresses. When ordering include the following information:

1. Instrument Model Number

2. Instrument Serial Number

3. Parts Description

4. Circuit Designation (if applicable)

5. Keithley Part Number If anadditional instruction manual is required, order the

manual package (Keithley Part Number 775-901-00). The manual package contains an instruction manual and any applicable addenda.

7.4 FACTORY SERVICE

If the instrument is to be returned to the factory for ser-

vice, please complete the service form which follows this section and return it with the instrument.

7.5 SCHEMATIC DIAGRAMS AND

COMPONENT LOCATION DRAWINGS

Schematic diagrams and component location drawings follow the appropriate replaceable parts list for that particular board.

7-1

REPLACEABLE PARTS

Table 7-1. Mother Board, Parts Llst

Circuit I I Keithlev

Desig. ::

c3 ;: :;

C8 EO

Cl1 CL?

cl3

Cl4 :iz

Cl7 Cl8 Cl9 c20

c21 c22 C23 C24 C25 C26

t27

I-

C28 C29 c30 c31 C32 c33 c34 c35 C36 c37

C38 c39 c40 c41 C42 c43 c44 c45 C46 c47

Desaiution Capacitor Ceramic, 0.1~

Capacitor Ceramic, 0.1~ Capacitor Tantalum, 3.3~ Caoacitor Ceramic. 0.1~ Capacitor Ceramic; 0.1; Capacitor Ceramic, 0.1~ Capacitor Electrolytic, loop, 16V Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Myler, 33n, 250V Capacitor Ceramic, 3.3p

Selected value l5p-18p Mica Capacitor Ceramic, 0.1~ Capacitor Myler, lOn, 250V Capacitor Ceramic, 33p Capacitor Ceramic, 0.1~ Capacitor Ceramic, O.lfi Capacitor Ceramic, 0.1~. Capacitor Ceramic, 33p Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~1 Capacitor Ceramic, 33p Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.11 Capacitor Ceramic, 0.1~ Ca~cibr Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor, Myler, 33~ 250V

Capacitor Ceramic, 3.3p Selected value l5p-18p, Mica

Capacitor, Myler, lOn, 250V

Capacitor Ceramic, 33p Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 33p Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 33p Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~ Capacitor Ceramic, 0.1~

Rut Ntimber

C-237-0.1 C-237-0.1 Kl540-0335 c-237-0.1 c-237-0.1 c-237-0.1 KL532-0107 c-237-0.1 C-237-0.1

c-237-0.1 Kl521-0333 Kl500-03ti

C-237-0.1 Kl521-0103 Kl5W0330 C-237-0.1 c-237-0.1 c-237-0.1 KISOO-0330 C-237-0.1

c-237-0.1

Kl500-0330

C-237-0.1 C-237-0.1 C-237-0.1 C-237-0.1 C-237-0.1 C-237-0.1 C-237-0.1 Kl521-0330 Kl500-03R3

Kl521-0103 KISOO-0330

C-237-0.1

C-237-0.1 C-237-0.1 Kl500-0330 C-237-0.1 C-237-0.1 KL500-0330 C-237-0.1

C-237-0.1 c-237-0.1 C-237-0.1 C-237-0.1

7-2

Tektronix 775A Instruction Manual

Specifications and Main Features

Frequently Asked Questions

User Manual