Keithley 775A User manual

All references to the 775 instrument in this manual apply to the 775A
©1985, Keithiey Instrumeiits, Inc.
Instrument Division
Cleveland, Ohio, U.S.A,

Keithiey Instruments, inc, warrants this product to be free from defects
in materia! and worf:<^3nship for a period of 1year from dais of ship-
ment. During th© warranty period, we will, at our option, either repair
or repiacs any product that proves to be defective.
To exercise this warranty, writ© or call your iocs! Keithley represent-
ative, or contact Keithley headquarters in Cievaiand, Ohio. You will be
given prompt assistance and return instructions. Send the instrument,
transportation prspaid, to the indicated service TadHty. Repairs will be
made and the instrument returned, transportation prepaid. Repaired
products are warranted for the balance cf the original warranty period,
or at least 90 days.
LIIVliTATlOW OF VmRBAiyTY
This warranty does not apply to defects resulting from unauthonzsd
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 ail other warranties, sxpre-ssed or implied, in-
ciuding sriy irnpiisd warranty of merchantability or fitness for apar-
ticular use. Keithley instruments., !nc. shall not be iiabieforany indirect,
speciai or consequential damages.
This instrument has been inspected and tested in sccordance 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 cenifiad standards maintained In
the Laboratories of Keithley instruments, inc,
KEITHLEY
KEITHLSV INSTRUMENTS. INC.
INSTRUHEHT DIVISION /28775 Aurora Road /Clevaiand, Ohio 44139 /U,S;A. /l2l6i 248-0400 /Telex: 98-5469
WEST agRMANYs K«lthlsy Instruments GmbH /Heiglhofstr, 5/8000 Munchen 70 /[phone] /Telex: 52-12160
aRE/.T BRITAIN: KeltNty Instruments, Ud. /1,Bouitor^ Road /Reading, Berkshire RG 2ONL/ (0734) 86-1 2-87/88 /Talex; 84-7047
FRANCE? Ksithisy Initrumente SARL /2, Bis Rue Ison Bium /B.P, 60/91121 Paiaiseau Cedex /(6) 011-51-55 /Telex; 600-933
NfTHEiRLANDS: Keithley Instruments BV /Arkeissdijk 4/Postbus 559 /4200 AN Go?'!nchem /(0) 1830-25577 /Telex: 24-684
SWITZERLAND: Keithley instruments SA /Krieabechstr, 4/8800 Dubendorf /01/821-S4-44 /Telex: 57-536
AUSTRIA: Keithley Instruments Gss.m.b.H, /Dobiinger Haupstr. 32 /1130 Wien /314 289 /Telex: 13-4500
ITALY; Kiithlsy Instruments, .SRL /Viale S. Gimignano 4/A /20100 Milarw, Italy /4120360

INPUT CHARACTERISTICS PERIOD A
Channel A, B; each channsi
RANGE.' 0to 12CMHz, dc coupled,
to 120MHZ; ac coupled.
SENSmVir/ (xl); 25mV nns, <10MHz,
50mV rm >10MHz.
DYNAMIC RANGE (xl): 50mV to 5V pk-pk, <20MHz.
i40mV to 2.5V pk-pk. >20MHz.
COUPLING: ac or dc, switchable.
IMPEDANCE: IMO nominaL, shuoted bj? <60pF,
ATTENUATOR: xl or xl0 nominal, switchable.
LX3W PASS FILTER: -lOdB at lOOkHz nominal, switchable.
SIGNAL OPERATING RANGE (xl>? -2,55V dc to -2,55V dc.
TRIGGER LEVEL: -2.55V dc to +2.55V dc, xl,
'25.5V dc to +25.5V dc, xlO,
TRIGGER LEVEL RESOLUTION! lOmV, ,xl,
lOOmV, xir.
TRIGGER LEVEL SHTHNC ACCURAO-!
±(35mV +2% of setting), xl,
±(350mV f2% of setting), xli)
TRIGGER LEVEL SETONG--OUTPUT: via rear panel BNC,
not adjusted for attenuators.
•SLOPE: +or -slope, switehable.
DAMAGE LEVEL:
xl: .dc=2kHz 25CfV dc 4- peak ac
2kHz-’i00kHz 5x10^' rms^Hz/frequencv
>100kHz 5V rms •
xJD: dc-20kHz
20kHz'100kHi
>10QkHz
250V dc -f peak ac
5X10"V rryi3®Hz,''irequency
50V' rms
R/VNGEi 10ns to 10" seconds.
LSD DISPLAYED: 10ns to 0.1ms.
ACCURACY:
±1 LSD ±{Time .Base Error xPeriod) ±Trigger Error.
RANGE: 10ns to lOsec.
LSD DISPIAVSD: (10ns xPeriod),/Gate Time.
RESOLUTION:
,, ,(1.4 XTV^er Error -i- 2ns) xPeriod
±.t Lbu ±^—
Gate llirie
ACCURACY: ±Resolution ^(Time Base Error xPeriod)
NUMBER OF PERIODS AVERAGED: Gate Time/Period
RA.NGE: IGns to 10^ seconds.
LSD DISPLAYED: 10ns to 0.1ms.
ACCURACY: ±1 LSD ±(Time Base Error xTime interval;
±Trigger Error ±Trigger Tuning Error ±2ns.
PULSE WTETTH A(Positive or Negative)
RANGE: lOns to K)" seconds.
LSD DU5PL.AYED; 10ns to 0.1ms.
ACCURACY: ±1 LSD ±(Time Base Error xPulse Width)
tTrigger Error ±Trigger Timing Error +2n.'>,
TOTALIZE A
Channel C(with Model 7751 option)
RANGE: SOMHz to 1.3GHz.
SENSITIVITY: 15mV, 50MHz to l.OGHz:
25mV, 1.0GHz to 1.2GHz;
;^mV, 1.2GHz to 1.3GHz
DYNAMIC lU^NGE: 25mV rms to IV rms.
COUPLING: ac,
IMPEDANCE: 5CQ.
DAMAGE LEVEL:
dC'lOQkHz 15V dc -r peak ac
>100kHz 5V rms
FREQUENCY A, B
RANGE: O.lHz to OOMHz,
LSD DISPLAYED: (10ns xFrequency)/Cate Time
RESOLUTION:
1\SD ^Tri^er Error -r 2ns)x Frequency
G^e Time
ACCURACY:
iResoiution ±(Time Base Error xFrequency)
DIGITS DISPL.4YED: 8per second of Gate Time, minimum.
MOOES: Cunuiiative or .A gated by B
RANGE: 0to 10** -1
REPETITION RATE: 120MHz max.
LSD DISPLiWED: 1count up to 10*®--!, then 9most sigmd'
cant dig,its.
ACCURACY: *1 LSD
GATH/DELAY
INTERNAL GATE TIME; Variable from. lOO^ts to lOsec in 43
increments, or one period of the input, whichever is longer,
May be used in Frequency and Period Average
measurements.
EXTERNAL GATE TIME: Contmuou.sly variable horn. 100/is
to IDsec; or one period of the input, whichever is longer.
EXT’ERNAL GATE DELAY: 10/iS +one period, of the
input .signal, maximum.
INTERNAL DELAY TIME: Variable from lOtV to iOsec m45
increments. May be used in Period, Time Interval and Pulse
Width mea-surements.
EXTERNAL DELAY TIME; Continuously variable from 100,us
to >1 hour.
EXTERNAL GATE/DELAY INPUT: Positive TTL signal via
rear panel BNC.

FREQUENCY; IOMH2.
AGING RATE; s5 xW“^/niORth.
THMPERAruaS; ±5 xK>“"e 0® to 40®C ref 25*C.
TCXO {with ModgI 7732 option)
FREQUENCY: lOMHz
AGING RATE: <1 xlO-’/month,
1‘EMPERAXURB: ±1 x10-^ 0to 4(FC ref 25*C.
UNB VOIXAGE: <1 x10“^ for 10% change,
IEEE488 INTERFACE
MULTILINE COMMANDS; DCL, LLO, SDC, GET, GTL,
UNX UNI, SPE, SFD.
UNIUNE COMMANDS; IFC, MK EOl, SRQ, ATN.
iNTSmCE FUNCTIONS; SHI, AHl, T6, TEO, U, LEO, SRI,
PPO, DCl, on, CO, El.
PROGRAMMABLE PARAMETERS; All front panel corttrob
(except I^WER) phos Reading Rate, Data Format, Trigger,
SOI, Termiiiatot, Service Request, Seif Test, Display, Status,
READING SATES; one shot, normal fS/serond), fast
(2f;/second), or dump (I'W/seeond),
DISPLAY; Nine LhD digits with decimal point and exponent,
BENCH reading RATHS: One shot, or normal (3/seccnd).
ARMING (TRIGGER); Each channel is amied by it's ov/n
signal; or RESET button or EXT ARMING input when in one
shot (HOLD) mode.
ARMING DELAY: '^fis in Frequency and Period Average;
iDgs in Period, Hme Interval and Pulse Width.
EXTERNAL ARMING INPUT. Positive edge TTL signal via
rear panel BNC.
EXTERNAL TIME BASE INPUT: lOMHz TTL signal via rear
panel BNG
TIME BASE: OUT: 2V minimum @lOMHz, lOOfl output resis-
tance, via rear pane! BNC.
GATE: LED Indicator lights when gate is open.
WARMUP: 2hours to rated accuracy ar;d stability,
OPERATING TEMPEKAIXIHE: 0^ to 40"C, 0% to 80% relative
huuiidity.
STORAGE TEMPERATURE: -25'^ to 65^C.
POWER: 103-125V or 2Y3-250V (rear panel switch selected),
5O-6OH2,35VA max, 90-1'UTv avadabie.
DIMENSIONS, WEIGHT: 127mm high x215mm wide x
359mm deep (5"x 8*/(i"x
Net weight 3.5kg (8 lbs).
Speciticiuions subject to change without notice.

SECTION 1-GENERAi INFORMATION
1.1 INTRODUCTION M
1,2 MODEL 775 FEATURES 1-1
1,3 ,WARRANTY INFOI^vtATION l-l
1:4 MANUAL ADDENDA ,M
1.5 SAFETY SYMBOLS AND TERMS 11
J.-I
1.6 INSPECTION 1-2
1.7 USING THE MODEL 775 MANUAL 1-2
1,8 ACCESSORIES 1-2
SECnON 2-BASIC COUNTER/TIMER
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
FRONT PANEL FAMILlARlZATIOs\i
Controls
Terminals
Display and Indicators
Tilt Bail
REAR PANEL FAMILIARIZATION
Connectors and Terminals
Line Vbkage Selector Switch
IEEE-488 Address Switches
Line Fuse
POWER-UP PROCEDURE
DISPLAY MESSAGES
No Option Message
CONTROL SELECTION
Function
Selecting Gate Time
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
2-4
2-4
2-6
2-6
2-6
2-6
2-6
2-8
2-9
2-9
2-10
2-10
2-10
2-11
.Ml
2-12
2-1.2
2•12
2-13
2-13
2-13
ECTIOK 3-IEEE-488 OPERATION
3-1
O' i
3.1
3.2
INTRODUCTION ..
BUS DESCRIPTION

3,3 IEEE'488 BUS LINES
3, 3. ,IBus Management Lines
3.3.2 Handshake Lines -
3.3.3 Data Lines
3,4 BUS COMMANDS
3,4,1. Uniline Commands
3.4.2 Uruvetsal Commands
3.4.3 Addressed Commands
3.4.4 Unaddressed Commands
3.4.5 Device-Dependent Commands
3.5 COMMAND CODES
3.6 COMMAND SEQUENCE
3.6.1 Addressed Command Sequence
3,6, 2- Universal Command Sequence
3,6,3
Device-Dependent Command Sequence
3.7 HARDWARE CONSIDERATIONS
3.7.1 Typical Controlled Systems
3.7.2 Bus Connections
3.7.3 Primary Address Programming
3.8 SOFTWARE CONSIDERATIONS
.1,8.1 Controlled Interface Routines
3„8,2 HP-8 BASIC Statements
3.8.3 Interface Function Codes
.3.S.4 Model 775 Interface Commands
3.9 GENERAL BUS COMMAND PROGRAMMING
3.9.1 REN (Remote Enable)
3.9.2 IFC (Interface Clear)
3.9.3 LLO (Local Lockout)
3.9.4 GTL (Go To local)
3.9.5 DCL (Device Gear)
3.9.6 SDC (Selective Device Clear)
3.9.7 GET {'Group E.xecute Trigger)
3.9.8 Serial’ PoiUng (SPE, SPD)
3.;10 DEVICE-DEPENDENT COMM,AND PROGRAMMING
3, .10, !Execute (X)
1.10.2 Function (F)
3.10.3 Channels A, B Coupling (AC, 6C)
3. !04 Channels A, BAttenuator (AA., BA) .
3.10.5 Channels A, BFilter (.AF, BF)
3.10.6 Channels A, BSlope (AS, BS)
3.10 7Channels A, BTrigger Level (AL, BL)
:U0,B Rate (S) V
3.10.9 Gate Time (G)
3.10.10 Delay Time (W)
.3.10.11 Delay (1)
3.10.12 Displayed Digits (N)
Triggering (T)
3,10.14 EOl (K)
3.10.13 SRQ Mode (M) and Serial Poll Status Byte Format .
3,10.16 Displayed Modes (D)
.3,10,17 .Self-Test 0)
3.11 READING FROM THE MODEL 775
3,11,'i Data Control Commands (B)
.U1.2 Status Word (U)
3.
.
11. 3Terminator (Yi
.3.11.4 Prefix (P)
3.. .,5 Dump Mode (S3 Rate Mode)
..! ,.3-2
3-3
3-3
3-4
3-4
3-3
3-5
3-5
3-5
3-6
3-6
3-6
3-6
3-6
3-6
3-8
.... 3-10
3-'i0
... ,3-10
.... 3-11
...
,
3-12
...
.
3-13
.. .
.
3-13
.,,.3-13
., , .3-14
. . ,.3-14
, , ,.3-14
. . . , 3-15
.,..345
,,, , 3-15
.. . ,3-16
...,3-16
..,.3-19
, , , , 3-19
,,,,3-19'
, . . 3-20
.,.3-2U
.,.3-20
...3-20
.-.3-21
,,.3-22
..,3-22
... 3-23
.,.3-23
... 3-23
... 3-23
...3-24
...3-26
...3-27
.,.3-27
..,3-2.8
.,.3-29
... 3-30
... 3-31
,.,3-31

3-12
3.12.1
3.12.2
FRONT PANEL ,PROGRAIv&4!NG 3-34
IDDC Error.... 3-34
IDDCO Hrror 3-34
SECTION 4—PERPORMANCE VERIFICATION
4.1 INTRODUCnON 4-1
4.2 ENVIRONMENTAL CONDITIONS 4-1
4.3 RECOMMENDED TEST EQUIPMENT 4-1
4.4 INITIAL CONDITIONS 44
4.5 VERIFICATION PROCEDURES 44
4.5.1 Channels A, Band CInput Sensitivity 4-2
4.5.2 r^riod Measurement Accui'acy Check 4-2
4:5.3 Period Averaged Measurement Accuracy Check 4-2
4.5.4 Tune Interval A—BMeasurement Operation Check 4-2
4.5.5 Pulse AMeasiirement Operation Check 4-3
4.5.6 Delay Operation Check 4-3
4.5.7 ,External Gate Operation Check 4-3
4.5.8 Arming Operation Check 4-3
4.5.9 Model 7752 TCXO Accuracy Check 4-4
5—THEORY OF
5,1 INTRODUCTION 3-1
5.2 OVERALL FUNCnONAL F3ESCRIPTION ,,
.
3-1
^3ANALOG CIRCUITRY
5.3,1 Input Circuits Aand B
5.3,2 Input Circuit C
5.3.3 iOMHz Standard Reference Osdllator ,,,,
.
• . .,'‘"3
5.3,4 lOMHz TCXO Referertce Oscillator
53.5 '^
5.3.6 '' Measurement Section
5.3,7 Power Supply
5,4 DIGHAL CIRCUITRY ,.5-13
5,4.1 Microcomputer Block Diagram
5.4.2 Memory Mapping •'.1'
5,4,3 Address Decoding
5,4,4 K>yboard/0isplay Interface 5-M
5,4.5 IEEE Interface
SECTION 6-MAINTENANCE
6.1 INTRODUCTION 6T
6.2 LINE VOLTAGE SELECTION 6-1
6,3 FUSE REPLACEMENT 6-1
6,4 USING AN EXTERNAL TIME BASE 6-2
6,5 MODEL 7751 CHANNEL COFiTON INSTALLATION 6-3
6,6 MODEL 7752 TCXO OPTION INSTALLATION 6-4
6,7 CALIBRATION 6-5
6,7.1 Environmental Conditions 6-3
6,7,2 Warm-Up Period 6-.5
6,7.3 Recommended Thst Equipment -6-5
6,7.4 Calibration Procedure 6-5
6,75 Multiplier Adjustment -6-7

6.7.6 Adjustment
6.7.7 Channels Aand BSensitivity Adjustment
6,7,S Inputs Aand BAttenuator Compensation
6.79 Time Base Mjustment (Standard 5PPM Tune Base) ..
.
6,710 Time Base Adjustment (Optional 1PPM Time Base) ,,
.
6.8 SPECIAL HANDLING OF STATIC SENSITIVE DEVICES
6.9 DISASSEMBLY iNSTRUCHONS
6.10 TROUBLESHOOTING
6.10.1 Recommended Test Equipment
6.10.2 Power-Up Seif Diagnostics
6.10.3 Power Supply Checks
6.10.4 Reference Oscillator and Clock Checks
6, 10, .5 Digital Circuitry and Display Checks
6.10.6 Sigirai Coriditioning and Input Circuit Checks
6.10.7 Multiplier Circuit Checks
6.10.8 Trigger Level Checks
6.10.9 Measurement Section Checks
6-7
6-7
6-7
6-7
6-7
6-8
6-8
6-10
6-10
6-10
6-10
6-11
6-11
6-11
6-n
6-n
6-11
SECnON 7-^REPLACEABLE PART:
INTRODUCTION
PARTS LIST
ORDERING INFOILM^TION
RACTORY SERVICE
SCHEMATIC DLA.GRAM A.ND COMPONENT IDCAJION DRAWING!
APPENDIX
INDEX
7.1
7.2
7-3
7.4
7.5
7-1
7-1
7-1
7-1
7-1
-A-1
14
V

24 Mode! 775 Front Panel 2-2
2-2 Model 775 Rear Panel 2•^3
2-3 Fall Tinie Measurement 2-14
2-4 Using Delay to Measure Contact Dwell Time 2-!5
2-5 High Frequency Multiplexed Measurements 2-15
34
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
IEEE Bus Configuration
IFXE Handshake Sequence
Command Codes
System Types
IEEE-4^ Connector
IEEE-4!^ Connections
Rear Panel of Model 775 Showing IEEE connector
Contact Assignments
Typical IEEE»488 Bus Driver (One of 16)
IEEE-488 Display Error Messages , ,
,
3-2.
3-3
3-7
3-8
3-8
,3-9
3-9
3-9
340
3-33
54 Model 775 Simplified Block Diagram 3-2
5-2 Frequency AMeasurement Block Diagram :5-6
5-3 Frequency BMeasurement Block Diagram 5-7
5-4 Frequenc)'- CMeasurement Block Diagram ,:5-S
5-5 Period AMeasurement Block Diagram 5-9
5-6 rtme Intan-^l A-*B Measurement Block Diagram 5-10
5-7 Pulse Width Measurement Block Diagram. :3-H
5-8 Microcomputer Block Diagram 5-12
64 Model 775 -Standard 5ppm Tirrsebase d-2
6-2 Model 7751 Installation .6-3
6-3 Model 7752 Installation 6-4
6-4 Model 775 Calibration Adjustments 6-o
6-
5Model 775 Exploded View 6-9
74 Mother Board, Component Location Drawing /-ll
7-
2Mother Board, Schematic Diagram 7-.i3
7-3 Display Board, Component Location Drawing 7-26
7-4 Display Board, Schematic Diagram . . ..7-27
7-5 Model 7751, Component location Drawing 7-29
7-6 -Model 7751, Schematic Diagram 7-30
7-7 Model 7752, Component Location Drawing 7-31
7-8 Model 7752, Schematic Diagram 7-32
7-9 5ppm Oscillator, Component location Drawing 7-33
740 5ppm Oscillator, Schematic Location Diagram 7-34
V

i
2-1 Gate/Delay Deterinmatioii 2-8
2-
2Alarm Condition 2-13
3-
1rEEE-488 Bus Command Summary 3-4
3-2 Hexadecimal and Decimal Command Codes ri-Ci
3-3 Typical Addressed Command Sequence 3-ft
3-4 Typical Device-Dependent Command Sequence 3-6
3-5 fEEE Contact Designations 3-9
3-6 HP-85 IEEE-488 BASIC Statements 3-11
3-7 Model 775 Interface Function Codes 3-12
3-8 IEEE Command Groups 3-13
3-9 General Bus Commands ^-13
3-10 Default Conditions {Status Upon Power Up or After SDC or DCL) 3-15
3-n Device-Dependent Commar\d Summary 3-I7
3-12 Rate Commands 3-21
3-J3 Gate/Delay Time Predetermined Value 3-23
3-14 SRQ Mask Commands 3-24
3-15 SRQ Mask Legal Commands 3-25
,3-lb Status Byte Interpretation 3-26
3-L7 Data String Format 3-28
3-18 Prefixes .3-29
3-19 Status Vvbrd Format 3-30
3-20 Dump Mode Specifications. ,*3-33
3-21 Dump Ouput Mode Result Calculation 3-34
4-
1Recommended Test Equipment for Performance Verification
5-
1Model 775 Memory Mapping
6T Line Fuse Selection 6-1
b-2 Recommended Test Equipment tor Calibration 6-5
6-3 Static Sensitive Device 6-8
6-4 Recommended Minimum Test Equipment for Troubleshooting 6-!0
6-5 Power Supply Checks 6-11
6-6 Reference Oscillator and Clock Checks 6-12
6-7 Digital Circu'itr/ and Display Checks 6-12
6-8 Signal Conditioning Checks 6-1.3
6-9 input Circuit Checks 6-13
6-1.0 Multiplier Circuit Checks 6-1,3
6-
11 Trigger Level Circuit Checks 6-14
0-12 Measuring Section Circuit Checks 6-14
7'1 Mother Board, Parts List 7-2
7
-
2Display Board, Parts List 7-25
7-3 Mode) 775 Mechanical Parts List 7-3.5

35mV 35mV
TImi? Bagig base error is the maximum frac-
tional frequenc/ change in the time base frequency due
to all errors (e.g. aging, temperature, line voltage).
TVIfiger 6rrQf«~
ej2 -f
Input Slew Rate at Trigger Point
Where:
sj i.«5 the RMS noise voltage of the counter's input channel
(250uV typical).
Trigger
Input Slew Rate at Start Input Slew Rate at Stop
Trigger Point Trigger Point
Arming (Trigger) Delay—External arming delay
is the time from the positive going slope of the arming
signal to the internai gate open signal.
External O.&W OsSay—Extemal gate delay is the time from
the positive going slope of the gating signal to tire mtcr'
Hill gate open signal
Crt is^the RMS noise of the input signal for I2OMH2
bandwidth.
tSD-“Unit value ofthf least significant digit, Calculations
should be rounded ss follows: 1to UHz becomes IHz,
l.insec to ibnsec becomes lOnsec, etc.

1.1
INTRODUCTiON
The Keithley Model 775 Programmable Couhter/Timer is
anine digit, microcomputer based, fully programmable,
universal counter/timer. The Model 775 measures with
high resolution the following parameters:
®Frequency A
«Frequency B
eFrequency C
sPeriod
«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 9digite with an additional digit for ex*
ponent. The buEt-in interface makes the instrument fully
programmable over the IEEE-488 bus.
The Model 775 contains aprogrammable 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 ^%), Gate time is programmed in 46 steps
from lOO.ttsec to lOsec or external from the front panel or
over the bus.
1.2
MODEL 775 FEATURES
Dual Channel Capability—Dual channel capability with
two similar channels up to TlOMHz.
Trigger Delay Channel B—This feature is important for
some channel ABtime measurements,
True DC Coupling—Allows the Model 775 to do channel
A“* Bnaeasureinents.
Reciprocal Techr\ique—This counting method provides ad-
vantages over all traditional counters from DC up to the
dock frequency (lODMH?.)- The constant relative resoiu-
lion (8 digits/second independent of input frequencv)
makes it even more useful for low frequency applkalions.
1.3
WARRANTY INFORMATION
’Warranty information may be found on the inside front
cover of this manual. Should it become necessary to exer-
cise the warranty contact your Keithley representative or
the factory to determine the proper course, of .action.
Keithley Instruments maintains service facilities the
United States, United Kingdom and throughout Europe,
Information concerning the application, operation or .ser-
vice of your instrument may be directed to the applications
engineer at any of these locations. Check the inside rroni:
cover for addres,ses.
1.4 MANUAL ADDENDA
Information concerning improvements or change.? to the
instrument which occur after the printing of this nunuiai
wdli be found on an addendum sheet induded with this
manual Be sure to review these changes before attemp-
ting to operate or service the insfrument.
Full Programmability—Full programmability of all func-
tions and modes including different SRQ masks and chan-
nel selection.
High Frequency Option—HF-option adds a third measure-
ment channel for frequencies up to IGHz,
High Resolution—AlOOMHz clock rate, along with the
latest technique In frequency counting (reciprocal techni-
que), provides the high resolution of 8digits.^second or iHz
out of alOOMHz input signal.
1.5 SAFETY SYMBOLS AND TERMS
The following safety symbols and terms are used in this
manual or found on the Model 775.
The AiA symbol on the instrument denotes that the user
should refer to the operating instructions in this manual
Tlie WARNING used in this manual explain? danger? that
could result in personal injury or death.

:N£BAi. INI
The CAUTION used in this manual explains hazards that
could damage the instrument.
1,6 INSPECTION
The Model 775 was inspected both mechanically and elec*
thcaliy 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 resbipment is
necessary, The following items are shipped with every
Model 775.
Model 775 Programmable Counter/Timer
Model 775 Instruction Marmal
Additional accessories as ordered.
If an additional instruction Manual is required, order the
manual package (Keithiey part number 775-901*00), The
manual package includes an instruction manual and any
applicable addenda.
ivlodei 1019S Slide Rack Mount—The Model 1019S is a
sliding rack mount kit that allows the Mode! 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 70(?7 IEEE-488 Shielded Cables-The Model 7007
connects the Model 775 to the IEEE-488 bu-s using shield-
ed cables to reduce electromagnetic interference (EMI), The
Model 7007-1 is one meter in length and has an. EMI shield-
ed IEEE-488 connecdOT at each end. The Model 7007-2 is
identical to the Model 7007-1, bur is two meters in length.
Mode! 7008 IEEE488 Cables-Tlie Model 7008 connects the
Model 775 to the IEEE-488 bus. The Model 7008-3 Is 0,9m
(3 ft.) in length and has astandard IEEE-488 connector at
each end. The Model 7008-6 cable is identical to the Mode!
7008-3, but is 1.8m (6 ft.) in length.
Model 7051 B?4C to BMC Cable—Tne Model 7051 is 1,5m
(5 ft.) in length and is terminated on each end with aBNC
plug.
Model 7751 IGHz Channel COption—The Model 7751 is
afactor)’-msta!led option which provides athird channel
(C) for measuring frequencies between 50MHz and IGHz,
UOii MODEL
*Section 1contains general information about the
instrument.
«Section 2 contains detailed operating information on us-
ing the front panel corxtrols and rear panel terminals.
®Section 3contains information necessary to operate the
Model 775 over the IEEE-488 bus.
*Sectior'i 4contains performance verification procedures
tor the instrument. This information is helpful if you
'wish to verify that the instrument is operating in com-
pliance with stated specifications,
Section 3contains adescription of operating theory,
*Section 6contains information for servicing the Instru-
ment ,This section includes information on line voltage
selection, fuse replacement, adjustments and
troubleshooting.
»Section 7contains replacement parts information,
Model 7752 TCXO—High Stability Crystal Oscillator
Option-T'he Model 7752 is afactory-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 (T3 rVj in length and is terminated on one end with
aBNC plug and on the other with two alligator dips.
Mode! 7755 .5QQ Feedthrough Termination—Tne Mode! 7755
IS aBNC to BNC adapter for terminating RG 58 cable in
its characteristic impedance. VSWR <1,1, DC -250MH/..
8NC BNC
PLUG JACK
The following optional accessories are available to enhance
the Model 775 capabilities.
Model 1019A Pb®d Rack Mount—The Model 1019A is asta-
tionary rack mount kit that allows the Model 775 to be
mounted in astandard 19 inch rack.

2.1 (NTRODUCTION
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, con-
sists of using the Model 775 to perform basic frequency
and time measurements, IEEE-4.88 programming can also
be used. These aspects are covered in detail in Sections
3and 4, Alayout of the fron.t and rear panels of the Model
775 are shown in Figures 2-1 and 2-2 respectively, includ-
ed is a. brief description of each control, terminal tind
indicator,
NOTE
Any front panel button push or IEEE device-
depei\dent command (see Section 3) will cause the
measurement to restart, which will affect, for ex-
ainple, ameasurement of the time from channels
Ato B.

;-£j FUNCTION GSOUP-
*FREQ button toggles measurement betwee-n frequency
at channel Aand frequency at channel B.
®PEI^OD button icsg^les measurement between the
period Aand period average A.
*'TIME button toggles masswrement between the time
interval and pulse width of A.
5MODE button places instrument in either the hold,
delay, both hold and delay, or normal mode.
IuLj chan C""Meaaures frequencies from 50MHz to IGHz
through channel C.
tiJ rNPyr SETTING GEOUF™
»DC/AC button toggles instrument between A.C and DC
coupling of the input signal.
*SLOPE button todies instrurtient between the positive
or negative edge trigger.
*A'ITEN burton toggiesinstrument between the xl and
xlO input attenuation.
*FUTR button toggles filter between on and off,
*LEVEL buttons select the threshold point on asignal
that the Instrument wiU trigger.
lU DISPLAY MODIFY GROUP-
*GATE/DELASf button modifies cUsplsy from nomtAl fre-
quency (or time reading) to gate time or delay time,
«TRIGGER LEVEL button ntodihes tlw display to show
trigger level of both channels Aand B.
®GATE/DELAY time buttons conttoh time
open, delay of gate closure and number of
displayed,
'These buttons increment or decrement the
lue by one step.
i7!
u—
—
iLOCAL—Enables front panel operation.
Resets display to initiate new measurement cy-
cle during normal or hold mode operation.
=CHAN Aused when making frequency’ and time
mea-isurements.
*CHAN Bused when making frequency' and time .A “• B
measurements.
«CHAN Cused when making high ttequenc/ measure-
ments up to iGHz with a5^ input impedance (7751
option), The shell is connected to chassis ground as
indicated by the isymbol,
DISPLAY AND INDICATORS-
«Display consists of anine digit mantissa and asingle
digit exponent.
«Range indicator consist of Hz, SEC, V. Hz is on dur-
ing frequency measurement. SEC is on during time
and period measurements, Vis on when TRIGGER
LEVEL button is pressed.
*Gate indicator blinks at arate proportional to gate
time,
»IEEE status indicators select either remote, taik or listen
w’hen programming over IEEE'488 bus.

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CONNECTORS AND TERMINALS-
^AC receptacle connects to athree wire line cord
which provides connection to the line voltage,
i* IEEE-488 connector is used to connect the instmmerst
to the IEEE-488 bus, IEEE interface functions are
marked above the connector,
«TRIGGER LEVEL OLniPUT connections are used to
connect the DC voltage level from the trigger circuits
to an external DI^ or oscilloscope, DC output range
is marled above the connector.
*CLOCK com^or is used to output the internal clock
as areference to another instrument or to use an ex-
ternal clock as the Model 775's time base.
«EXT ARlvflNC &GATE DELAY connector is used to
receive one ot three signals: aiming pulse, external
gate signal or external delay pulse.
LINE VOLTAGE SELECTOR switch selects to.e line
voltage that the unit 'A'iii operate on.
IEEE-488 address switches set the primary address for |
IEEI'-48S bus operation. I
FUSE provides protection on the A.C power line

2,2 FRONT PANEL FAMIOARIZaTION
Ills fror.t panel layout of the Model 775 is shown in Figiire
2*1. The front panes is generally divided into thi'ee sections;
controls, terminals, and display and indicators. Tlie follow-
ing 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 pimei controls may be divided into the following
functional groups: Function, Input Set-ting, Display Modify
and Gate.'Ddav Time.
POWER—d'rie POWER switch controis the A(" power to the
instrumeni. Depressing and releasing the switch ones
turns the power on. Depressing and releasing the switch
asecond time turns the power off.
Funedon Group—The four FUNCTION buttons control the
type of measurement.' Each button is used to select one
of two functions.
FR).-,Q—The FREQ button places the mstruinent in frequen^
cv measurement mode. Pressing the FREQ button once
turns she Aindicator on; Indicating the instrument is set
ior the trequenev A. mode. Pressing the button, a.second
time. :urn.S' the Bindicator on; indicating the instrument
i.s set .foi the frequency Bmode. Pressing of the FREQ but-
ton roggio.s the measurement between the frequency at
chanru-i Aand frequency at channel Bmodes.
PERIOD—The PERIOD button places the instrument in
period measurement mode. Pre.ssing the PERIOD button
once turns the Aindicator on; indicating the instrument
is in the period Amode. Pressing the PERIOD button a
second time, turns the AVG Aindicatoron; indicating the
instrument is in the period average Amode, Pressing of
the PERIOD button todies the measurement between the
period Aand period average A.
TIME—The TiMH button sets the Model 775 up to measure
the time interval benveen channel Aand B, Pressing the
TIfvlH button once turns the A—Bindicatoron; indicating
the instrument is in the time intenml A—Bmode. Press-
ing t'i'ie button asecond time, turns the PLS Aindicator
on: in'^icaiing the instrument is in the pulse Amode,
Pressi.,g of the TIME button todies the measui'ement beh
ween the time interv'al, A—Band pulse width of A.
MODE—Press the MODE button once to place the instni”-
rnent in the hold mode. Pt^ss the RESET button to dear
the display and take areading. The reading will be held
on the display until the RESET button is pressed again.
Pressing the MODE button asecond time, places she
Model in the delay mode of operation; the instrument
holds off closure of the gate for the selected delay time.
Pressing the MODE button athird time places the instru-
ment in both the hold and delay modes. Pressing of the
MODE button afourth time turns the indicators off; and
places the mstruinent in the normal mode of operation.
NOTE
The delay mode is disabled in the frequency and
period averaging modes.
FREQ C—The FKHQ Cbutton allows the Model 775 to
measure frequencies from 50MHz to IGHz on channel C,
Pressing the FREQ Cbutton turns the Cindicator on; in-
dicating the instrument is set to make high frequency
measurements on channel C. If the Model 7751 Channel
Coption is not installed, a'nO COPT message will be
displayed for tv/o seconds.
Input Setting Gitsiip—The six CHAN Apushbuttons cors-
trol input attenuation, coupling, slope, trigger level and
high frequency noise suppression. The six CHAN B
pushbuttons are functionalv identical to the CHAN A
buttons,
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 DOAC button turns
the AC indicator on; indicating the instrument is in the
AC coupling rnode. Pressing of the DC/AC button toggles
the instrument between AC and DC coupling or the in-
put signal.
SLOPE-The SLOPE button selects the slope that the
Model 775 will trigger on. In default position, the instru-
ment triggers on apositive going edge. Pressing the SIX^PE
button turns the “N"indicator on; indicating the in-
strument will ;trigger on anegative 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 at-
tenuated. Pressing the ATTEN button turns the xiO in-
dicator on; indicating that the instrument will attenuate
the signal b>' ID. Pressing of the ATTEN button toggles the
instmment betw^een the xl and xlD input attenuation. Note
that changing attenuation changes the trigger level, (e.g.
IV digger on xl goes to lOV on xlO).

FLTR—The FUT< button limits high frequency noise to
about lOOkHz through alow*pass filter mstalled at the in-
put terminal In default position, the iow-pass filter is off.
Pressing the FUR button turns the FLTR indicator on: in-
dicating that the low-pass filter is on. Pres.sing 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 (o.g. start and/or stop the
measurement inter/ai). Pressing. the Tbutton decrements
the level by one step. Pressing the Abutton Increments
the level by one step. Each step is lOmV on the xl attenuator
setting or lOOmV on the xlG attenuator setting. Holding the
level aor button in for mote than one second^ causes
the trigger level to continuously move up or down respec-
tively- Holding the LEVEL Aand Tbutton.® .in at the same
time, causes the instrument to jump to the preset posi-
tion O.OOV {or 00.0V).
Display Modify Group—The tYr-o pushbuttons in the
display modify group modify the display from, normal fre-
quency (ot time reading) to another reading such as trig-
ger level, gate time, delay time or displayed number of
digits.
GATE/DELAY-The GATE/DELAY pushbutton has two
functions; When instrument Is in the frequ.ency or pe.riod
averaged functtons, this button itiodifies the dispiav to
display the time that the gate remains open to complete
one cyde. When instrument is in the time interval, period
Aor pulse Afunction, this burton modihes the display
to show the time that the closure of the gate delayed
after its opening. Press GATE/DrXAY to exit.
Tl^JGGER LEVEL—The TRIGGER LEVEL butmn may be
used to modify the display to show the trigger iev\^I oi both
channels Aand B, Pressing the TRIGGER LEVEL button
turns the indicator above the button on, indicating that
the instrument -s 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 Aor CHAN
8[_evel buttons to modify the values, Press TRIGGER
LEVEL to exit.
Display Function—The display function allows the user tc.>
select the maximum number of most significant digits
which are to be displayed, In the normal operating mode,
the instrument will display amaximum of nine digits. The
minimum number of digits displayed is three. To access
the dispiav function press simultaneously the
GATH/DELAY and TRIGGER LEVEL buttons. Select the
number of digits to be displayed by pressing the
GATK/DELAY TIME Aor ^button to increment or decre-
meru the display. To resume normal operation, <iimpiy
press any other button on the front panel. The instrument
will display its measurements with the preselected number
of digits.
GArF./DELAy TIME-The tw-o GATEiDELAY rJvlE button.^
control: the time that the gate is opeir from lOfl^sec to lOsec:
in 46 steps; the delay of the gate closure from 100/isec to
lOsec in 46 increments; and the number of digits to be
displayed in increments of seven.
GATE/DELAY A, Each time the Abutton is pressed,
the gate or delay increments one step. Each time the
button i.s pressed, the gate or delay decrements one step.
If Aor ^button is held in for more than one .second, the
instram,ent will continuously increment or decrement. It
the A. and Tbuttons are held in at the same time, the
instnament will jump to apreset position of Lee delay time
or nine digits displayed numbers.
L’.3er Gate/Delay Function—Information on accessing thi.s
function will be given later in this chapter.
'LOCAIj—Pressing the LOCAL button w'hen the instru-
ment is i.n remote operation (but not in remote (local)
lockout condition)^ wOl place the instrument in iocal opera-
tion. Pressing this button when the instrument is aireadv
in local operation will have no effect on the instrument.
RKSET—Pres.sing the RESET button during norm.ri eper.,-;-
tion wiil reset the display and initiate anew mf.'.sfti’aernciu
cv'cle, When the instrument is in the hold mode of opera-
tion, pressing the RESET button dears the dispiav and
-lums the instrument for the next measurement.
2,2.2 Terminals
The termintiils are used to connect the Mode! 773 to the
.signal to be measured.
Channel A—The CHAN Aterminal is used when making
frequency and time m.easurements.
Channel B—The CHAN Bterminal is used when making
frequency and time A—Bmeasurements.
Channel C—The CHaN Cterminal is used (•or high fre-
quency measurements, up to IGHz with a5011! injiiit im-
pedance, Although this terminal is always instailed,, tlie
:internai ciraiitry needed to operate this function is optional
and may not be installed. BNC shell is connected to chassis
ground as indicated by the J. symbol.

2.2.3
Display and Indieatom
The function of the display and indicators is described
below,
Display~The display consists of anine digit mantissa and
asingle digit exponent. The exponent uses aleading 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
indicators,
Units Indicator,'.—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 LITvn*L button is pressed,
the V(volts) mdicator turns on.
GATE ]ndicator~When the instrument takes ameasure-
ment, the GATE indicator blinks at arate which is pro-
portional to the gate time.
IEEE Status indicators—The REMCTTE, TALK and LISTEN
indicator^; are used when programming the instrument
over the IHEE-488 bus. Refer to Section 3for compieto IEEE
programming information. These status indicators are not
operational during front panel instrument operation,
’'he tilt bail, which is located on the bottom cover of the
instrument, is useful for elevating the front of the instru-
ment to aconvenient viewing height, To extend, the bail,,
first rotate it 90~' away from the botton'\ cover and push up
on the leg to lock it into place, To retract the bail, pull the
leg-S 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 layout of the Model ^75,
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.
IEEE«4S8 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 DMM or oscilloscope. DC
output range is marked above the connectors.
CLOCK Connector—This BNC connector is used to out-
put the internal dock as a reference to another instrument,
The same input may be connected to an external dock
reference, To use an external clock reference, the internal
time base must be set for external operation. Refer to Sec-
tion 6for this procedure and proper signal levels to apply,
EXT ARMING &GATE/DELAY Connector--A BNC con-
nector which may receive one of three signals: arming
pulse, external gate signal or external delay pulse. This in-
put is useful when gate or delay times other than the in-
ternal times are required or to take one reading with the
Model 775 in synchronized with other equipment.
The LINE VOLTAGE SELECTOR switch selects the line
voltage that the Model 775 will operate on. For informa-
tion on voltage selection refer to Section 6.
2.3.3 IEEE-488 Address Switches
The IEEE-488 address switches are used to program the
primary, address for IEEE-488 interface operation .The ad-
dress may be set from 0 to 30.
2,3,4 Urn Fuse
The LINE FUSE provides protection for the .AC power line
input, For information on replacing this fuse, refer to Sec-
tion 6.
2.4
POWER-UP PROCEDURE
The basic procedure of powering up the Model 775 is
desciibed below,
1, Connect the female end of the power cord to the AC
receptacle on the rear panel. Connect the other end of
the power cord to agrounded AC outlet.