Keithley 3940 Operator's Manual

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Publication Date: March 1991
Document Number: 3940-900-01 Rev. .A

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WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a
period of 1 year from date of shipment.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables,
rechargeable batteries, diskettes, and documentation.

During the warranty period, we will, at our option, either repair or replace any product that proves to be de­fective.

To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in
Cleveland, Ohio. You will be given prompt assistance and return instructions. Send the product, transporta­tion prepaid, to the indicated service facility. Repairs will be made and the product returned, transportation
prepaid. Repaired or replaced products are warranted for the balance of the original warranty period, or at
least 90 days.

LIMITATION OF WARRANTY

This warranty does not apply to defects resulting from product modification without Keithley’s express writ­ten consent, or misuse of any product or part. This warranty also does not apply to fuses, software, non-re­chargeable batteries, damage from battery leakage, or problems arising from normal wear or failure to follow
instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING
ANY IMPLIED WARRANTY OF MERCHANT ABILITY OR FITNESS FOR A PARTICULAR USE. THE
REMEDIES PROVIDED HEREIN ARE BUYERS SOLE AND EXCLUSIVE REMEDIES.

NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR
ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT
OF THE USE OF ITS INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS
BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAM­AGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS OF REMOVAL AND INSTALLATION,
LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON, OR DAMAGE TO PROPERTY.

INSTRUMENTS

Instruments Division, Keithley Instruments, Inc.

WEST GERMANY: Keithky Instruments CmbH l Heiglhofstr. 5 l Munchen 70 l 089-71002-O l Telex: 52-12X% l Fax: [phone]
GREAT BRITAIN:
FRANCE
NIXHERLANDS:
SWITZERLAND:
AUSTRIA:
ITALY:

Koitbley Instruments, Ltd. l The Minster l St?, Portman Road l Reading, Berkshire RG 3 IEA l 01144 734 575 666 l Fax: [phone]
Keitbky Instruments SARL l 3 Allee des Garays . B.P. 60.91124 Palaiseau/Z.I. l I-6-0115 155. Telex: 600 933 l Fax:
Keithley Instruments BV l Avelingen West 49 l 4202 MS C&in&an l P.O. Box 559 l 4200 AN Gortnchem .0X+0-35333. Telex: 24 684 l Fax:
Keithley Instruments SA 0 Kriesbachstr. 4 l t%W Dubendorf l 01-821-9444 l Telex 828 472 l Fax: [phone]
Keitbley Instruments GesmbH l Rosenhugelstrasse 12 l A-1120 Vienna l (0222) 84 65 48 e Telex: 131677 l Fax: [phone]
Keitbley Instruments SRL l Vi&S. Gbnignano 4/A -20146 Mtlano .02-4120360 or M-4156540 l Fax [phone]

l

28775 Aurora Road l Cleveland, Ohio 44139 * [phone] l Fax: [phone]

1-6.0117726

01830-30821

Operator’s Manual

Model

3940

Multifunction Synthesizer

01991, Keithley Instruments, Inc.

All Rights Reserved

Instruments Division

Cleveland, Ohio, U. S. A.

Document Number: 3940-900-01

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

Safety Precautions

The following safety precautions should be observed before using the Model 3940 Multifunction Synthesizer and any
associated instruments.

This instrument is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety
precautions required to avoid possible injury. Read over this manual carefully before using the instrument.

Exercise extreme caution when a shock hazard is present at the test circuit. The American National Standards Institute

(ANSI) states that a shock hazard exists when voltage levels greater than 30V rms or 42.4V peak are present. A

safety

Inspect the connecting cables and test leads for possible wear, cracks, or breaks before each use.

practice

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

good

For maximum safety, do not touch the test cables or any instruments while power is applied to the circuit under test.
Turn off the power and discharge any capacitors before connecting or disconnecting cables from the instrument.

Do not touch any object which could provide a current path to the common side of the circuit under test or power line
(earth) ground. Always make measurements with dry hands while standing on a dry, insulated surface capable of with­standing the voltage being measured.

Instrumentation and accessories should not be connected to humans.

Table of Contents

SECTION 1 - General Information

1.1

1.2 FEATURES ...................................................................

1.3 WARRANTYINFORMATION

1.4 MANUALADDENDA ..........................................................

1.5 SAFETY TERMS AND SYMBOLS

1.6

1.6.1 Unpacking .................................................................

1.6.2 Shipment Contents

1.6.3 Operator’sManual

1.6.4 Repacking For Shipment

1.7 OPTIONAL ACCESSORIES

1.8 SPECIFICATIONS .............................................................

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

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

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

UNPACKING AND REPACKING

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

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

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

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

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

SECTION 2 - Getting Started

2.1 INTRODUCTION ..............................................................

2.2

2.2.1

2.2.2

2.3

2.3.1

2.3.2

2.3.3

2.4

2.5 BASICOPERATION .............................................................

2.5.1

2.5.2

2.5.3 Operating Examples

INSTALLATION ..............................................................

InstallationLocation..

Fan.. .....................................................................

LINE VOLTAGE SUPPLY

Line Voltage Selector Switch
Line Receptacle Connection

LineFuse ..................................................................

KANDLINGPRECAUTIONS .....................................................

FrontPanelSummary

Typical Test Connections

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

2-l
2-1
2-l
2-l
2-2
2-2
2-2
2-2
2-3

2-3
2-3
2-3
2-5

SECTION 3 - Operation

3.1 INTRODUCTION ..............................................................

3.2 FRONT PANEL AND REAR PANEL DESCRIPTION

3.2.1 Front Panel Description

3.2.2 RearPanelDescription ........................................................

3.3 Input and Output Connections

3.3.1 InputConnections ...........................................................

3.3.2 OutputConnections

3.4 STARTUP ....................................................................

3.5

3.5.1 Setting Parameters Using Numeric Keys

OPERATING PROCEDURES

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

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

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

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

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

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

3-l
3-l
3-l
3-12

3-14
3-15
3-16
3-17
3-17

3.5.2

3.5.3

3.5.4

3.5.5

3.5.6

3.5.7

3.5.8

3.5.9’

3.5.10

3.5.11

3.5.12

3.5.13

3.5.14

Setting Parameters with MODIFY
ErrorCodes
UnitsConversion
Frequency Programming
Amplitude Programming
DC Offset Programming
AC Amplitude and DC Offset Relational Restrictions
Waveform Selection, Square-Wave Duty Factor, and Synchronous Output
Oscillation Mode and Trigger Source Selection
Mark, Space, and Phase Parameter Programming
StopLeveland~S~C
SynchronousOperation
Frequency Sweep Operation

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

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

SECTION 4 - GPIB Interface

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

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

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

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

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

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

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

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

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

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

3-18
3-18
3-22
3-22
3-23
3-23
3-24

.................. 3-26

3-28
3-29
3-32
3-34
3-34

4.1

4.1.1

4.1.2

4.1.3

4.1.4

4.1.5

4.1.6

4.1.7

4.1.8

4.1.9

4.2

4.2.1

4.2.2

4.3

4.3.1

4.3.2

4.4

4.5

4.6

INTRODUCTION

GPIBOverview
Major GPIB Specifications
Bus Line Signals and Operation
GPIBHandshaking
Data Transfer Example
BasicTalkerFunctions
Basic Listener Functions
BasicControllerFunctions

Multi-Line Interface Messages ...................................................

OVERVIEW OF MODEL 3940 GPIB INTERFACE

Introduction
Specifications

MODEL 3940 PROGRAM CODES

Model 3940 Parameter-Setting Messages

Model 3940 Inquiry Messages
TYPICAL EXECUTION TIMES
PROGRAM CODE SUMMARY TABLE
SAMPLEPROGRAMS

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

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

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

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

........................................................... 4-2

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

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

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

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

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

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

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

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

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

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

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

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

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

4-l
4-l
4-l
4-2

4-3
4-3
4-4
4-4
4-4

4-6
4-6
4-6

4-13
4-13
4-26
4-35
4-40
4-45

List of Illustrations

SECTION 2 - Getting Started

Figure 2-l
Figure 2-2

FrontPanelSummary...................................................... 2-4

Typical Test Connections . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 3 - Operation

Figure 3-l FrontPanel
Figure 3-2
Figure 3-3
Figure 3-4
Figure 3-5 Main Synthesizer Sync Output
Figure 3-6 Sub Synthesizer Sync Output
Figure 3-7
Figure 3-8 Relational Range for Allowed AC Amplitude Voltage and DC Offset Voltage
Figure 3-9
Figure 3-10 BURSTOscillation
Figure 3-l 1 TriggerOscillation
Figure 3-12 GateOscillation
Figure 3-13
Figure 3-14
Figure 3-15
Figure 3-16
Figure 3-17 Phase Relationship after Phase Sync
Figure 3-18
Figure 3-19

RearPanel
Logic Input Circuits
Analog Input Circuit

Sweep Marker and Sync Outputs

Phase Relationship Between Waveform and Synchronous Output

Waveforms and Phase Definitions
Waveform Examples with Hold Stop Level
Waveform Examples with Reset Stop Level
Phase Sync Operation

Sweep Frequency and Sweep Output
SweepOperation

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

2-5

3-2
3-12
3-14
3-14
3-15
3-15
3-15
3-25
3-27
3-28
3-29
3-29

3-31
3-32
3-32
3-33
3-33
336
3-37

SECTION 4 - GPIB Interface

Figure 4-l Interface Connector
Figure 4-2

Figure 4-3
Figure 4-4

Figure 45 Response Output Format

Handshake Timing Diagram
Data Transfer Example
Program Code Syntax

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

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

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

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

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

4-2
4-3

44
4-7
4-9

SECTION 2 - Getting Started

List of Tables

Table 2-l

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

SECTION 3 - Operation

Table 3-l Main Synthesizer Amplitude Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table 3-2 Sub Synthesizer Amplitude Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 4 - GPIB Interface

Table 4-l
Table 4-2
Table 4-3
Table 4-4 Responses to Interface Messages
Table 4-5
Table 4-6
Table 4-7 Sub Synthesizer Parameter Setting Messages
Table 4-8
Table 4-9 Main Synthesizer Sweep Parameter Setting Messages
Table 4-10
Table 4-l 1
Table 412
Table 4-13 Main Synthesizer Parameter Inquiry Messages
Table 4-14 Sub Synthesizer Parameter Inquiry Messages
Table 4-15
Table 416 Main Synthesizer Sweep Parameter Inquiry Messages
Table 4-l 7
Table 4-18 Inquiry Messages for ARB Waveform Write and Readout Parameters
Table 4-19 Inquiry Messages for Parameters Specific to GPIB
Table 420
Table 4-21 Program Codes Summary

Multi-Line Interface Messages
InterfaceFunctions..
BusDriverSpecifications

StatusByte..
Main Synthesizer Parameter Setting Messages

Main Synthesizer Trigger Parameter Setting Messages

Miscellaneous Parameter Messages
ARB Waveform Write and Readout Messages
Parameters Specific to GPIB

Main Synthesizer Trigger Parameter Inquiry Messages

Inquiry Messages for Miscellaneous Parameters

Typical Execution Times

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

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

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

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

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

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

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

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

.............................. 420

............................................ 4-23

.................................... 4-24

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

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

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

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

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

.................................. 4-32

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

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

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

................................................... 4-40

3-20
3-20

4-5
4-6
4-6
4-7
412
4-13
4-16

4-25
4-26

4-28
4-29
4-30

4-33
434
4-35

SECTION 1

General Information

1 .l INTRODUCTION

The Model 3940 Multifunction Synthesizer is a multi­function oscillator integrated with two frequency synthe­sizers: the OHz to 2OMHz main synthesizer and the OHz
to 1OOkHz sub synthesizer. The Model 3940 can generate
the entire frequency band at a resolution of O.lmHz, with
an accuracy of tippm.

Five output waveforms,
available. In addition, arbitrary waveforms set with the
GPlB (IEEE-4881 interface can be generated by the main
synthesizer. Maximum output voltage for all waveforms
is 20V p-p (no load).

Since frequencies are synthesized directly by a custom
LSI digital IC, accuracy and stability are high, and the fre­quency switching time is short. Mother advantage is the
continuity of phase at frequency switchover.

Frequency sweep, half-cycle unit bursts of up to 32,768
cycles, trigger oscillation, and gate oscillation are avail­able with the main synthesizer. The square-wave duty
cycle is also variable. In addition, external signals can be
combined with the oscillator output to generate custom

waveforms.

%,%,-rL,n,and\,are

Frequency, amplitude, waveform, and phase can be in­dependently set on the sub synthesizer, which is not de­pendent upon the main synthesizer. The sub synthesizer
can also be used as a trigger oscillator for the main syn­thesizer.

Since the sub synthesizer and the main synthesizer use
the same clock source, the phase will not deviate when
the frequency is set with a whole number ratio.

The Model 3940 uses a two-line, 40-character liquid crys­tal display to display selected functions, parameters, and
pertinent messages. Parameter settings are easily made
using both the numeric keys and the modify knob.

The Model 3940 is equipped with a standard GPIB
(IEEE-4881 interface, and can be programmed over the
bus for the same operating modes and parameters that
can be controlled from the front panel.

The Model 3940 can be used as a multiphase oscillator
when combined with multiple identical units and used
with the optional synchronous cable.

1.2 FEATURES

1. Two integrated independent frequency synthesiz­ers: Main Synthesizer and Sub Synthesizer

l-l

SECTION 1
General Information

2.

Wide bandwidth; tippm frequency accuracy; and
phase continuity at frequency switchover.

Main Synthesizer: OHz to 2OMHz
(resolution: O.lmHz)
Sub Synthesizer: OHz to 1OOkHz
(resolution: O.lmHz)

3.

Five output waveforms available:
and\,( b th

bitrary waveforms, variable duty factor for square
waves (main synthesizer only).

4.

External signals can be added to the main synthe­sizer waveform output to synthesize additional
waveforms.

5.

Burst, trigger, gate oscillation, and frequency sweep
function (main synthesizer only).

6.

Multiphase oscillator operation with the use of the
optional synchronous cable and additional Model
3940 units.

su syn

esizer and main synthesizer); ar-

vb-L A,

The

WARNING

dangers that might result in personal injury or death. Al-

ways read the associated information very carefully be-

fore performing the indicated procedure.

The

CAUTION

hazards that could damage the instrument card. Such

damage may invalidate the warranty.

heading used in this manual explains

heading used in this manual explains

1.6 UNPACKING AND REPACKING

1.6.1

After carefully unpacking the instrument from its ship­ping carton, inspect it for any obvious signs of physical
damage. Report any such damage to the shipping agent
immediately. Save the original packing carton for storage
or possible future shipment.

Unpacking

1.3 WARRANTY INFORMATION

Warranty information is located on the inside front cover
of this operator’s manual. Should your Model 3940 re­quire warranty service, contact the Keithley representa­tive or authorized repair facility in your area for further
information. When returning the instrument for repair,
be sure to fill out and include the service form at the back
of this manual in order to provide the repair facility with
the necessary information.

1.4 MANUAL ADDENDA

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

1.5

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

SAFETY TERMS AND SYMBOLS

1.6.2

The following items are included with every Model 3940
order:

Model 3940 Multifunction Synthesizer
Model 3940 Operator’s Manual.
Power cord
Fuse 2A, 25OV, 5.2 x 20mm (contained in fuse holder as
spare fuse)
BNC to BNC signal cable
Additional accessories as ordered.

Shipment Contents

1.6.3 Operator’s Manual

If an additional manual is required, order the manual
package, Keithley part number 3940-900-00. The manual
package includes an operator’s manual and any perti­nent addenda.

1.6.4 Repacking For Shipment

Should it become necessary to return the Model 3940 for
repair, carefully pack the unit in its original packing car­ton or the equivalent. Be sure to use a cardboard box of
sufficient strength.

A

The ’

user should refer to the operating instructions.

l-2

symbol on the instrument indicates that the

Include the following information:

o Advise as to the warranty status of the instrument.

General Information

SECTION 2

l

Write ATTENTION REPAIR DEPARTMENT on the

shipping label.

l

Fill out and include the service form located at the back

of this manual.

1.7 OPTIONAL ACCESSORIES

The following accessories are available for use with the
Model 3940.

Model 3949 Synchronous Cable:

multiple Model 3940 units to be connected together to

form a multiphase oscillator.

Models 3900-l and 3900-2 Rack Mounting Kits:

Model 3900-2 mounts one Model 3940 in a standard 19

inch rack. The Model 3900-2 mounts two Model 3940s
side by side in a standard 19 inch rack. Both kits include
all necessary hardware for proper rack mounting of the
instruments.

Model 7007 Shielded IEEE-488 Cables:

7007-l (lm, 3.3ft.j and Model 7007-2 (2m, 6.6ft.j can be
used to interface the Model 3940 to the IEEE488 bus.

The Model 3949 allows

The

The Model

The Model 7051-2 is terminated with male BNC connec­tors on both ends.

Model 7051-5 BNC-to-BNC Cable:

The Model 7051-5 is
5OQ BNC to BNC cable (RG-58C) 5ft. (1.2m) in length.
The Model 70515 is terminated with male BNC connec­tors on both ends.

Model 7051-10 BNC-to BNC Cable:

The Model 7051-10 is
similar to the Models 7051-2 and 70515 except that it is
loft. in length.

Model 7754-3 BNC-to-Alligator Cable:

The Model
7754-3 is a 3ft. (0.9m) 5OQ cable (RG-58C), terminated
with a male BNC connector on one end and two alligator
clips on the other end.

Model 7755 5OQ Feed-Through Terminator:

The Model
7755 is a BNC to BNC adapter that is terminated with a
5OQ resistor. VSWR is ~1.1, DC to 25OMHz.

1.8 SPECIFICATIONS

Model 7051-2 BNC-to-BNC Cable:

The Model 7051-2 is

5OQ BNC to BNC cable (RG-58C) 2ft. (0.6m) in length.

Detailed Model 3940 specifications may be found in Ap­pendix B.

l-3

SECTION 2

Getting Started

2.1 INTRODUCTION

This sections contains basic information on installation
and power line connections; it also provides typical sim­ple operating examples.

2.2 INSTALLATION

The following paragraphs discuss Model 3940 installa­tion. In particular, use adequate care when installing the
unit. Improper installation will adversely affect the life,
reliability, and safety of the unit.

The Model 3940 weighs about 12 lbs. Be careful when car­rying the unit or mounting it in a rack.

2.2.1 Installation Location

Be sure to install the unit in a location that satisfies these
temperature and humidity conditions. Also the environ­ment must be free of dust and vibration, and the Model

3944

must not be exposed to direct sunlight.

The Model 3940 uses a line filter, but pulse noise or strong
magnetic or electric fields may cause incorrect operation
of the unit. Do not install the unit near a source of pulse
noise or strong magnetic or electric fields.

The guard on the rear panel of the unit is designed to pro­tect rear panel connectors and should not be used as a leg
for installation. Do not stand the unit vertically on the
rear guard because it may fall over, causing instrument
damage or personal injury.

2.2.2

The Model 3940 is air-cooled by a fan. Insufficient air flow
may cause components in the unit to fail. Follow the in­structions given below.

Fan

The allowable ambient temperature and humidity
ranges for the Model 3940 are.

Operating: 0” to 4O”C, 10 to 9O%RH
Storage: -10” to SO’C, 10 to 8O%RH

CAUTION
Observe the following precautions to pre­vent damage to the unit:

l An air intake port is provided on the rear

panel of the unit. Allow a space of at least

2-l

SECTION 2
Gettim Started

four inches between the rear panel and a
wall or other obstruction.

l An exhaust port is provided on the bottom

panel of the unit. Install the unit on a rigid,
flat surface, and avoid installing it on soft
material such as a cushion. Be careful not to
insert foreign material between the bottom
of the unit and the surface underneath. An­other exhaust port is located on the top panel
of the unit. Be careful not to block the top
port by placing an object on top of the unit.

* Avoid mounting two or more units vertically

(for example, when using two or more units
synchronously). Placing one unit on top of
another will obstruct the exhaust port.

l Dust collecting in the fan filter will prevent

sufficient air flow. In clean operating envi­ronments, wash the filter with a mild deter­gent every three months. When operating
the unit in a dusty environment, wash the fil­ter with a mild detergent at least once a
month.

l Immediately turn off the power to the unit if

the fan ceases to operate. Operating the in­strument with the fan inoperative may result
in damage to the instrument.

WARNING
Disconnect the power cord from the instru­ment before changing the supply voltage
setting.

CAUTION
Be sure to set the line voltage switch to the
correct position for the line power voltage to
be used. Operating the instrument on an in­correct voltage may cause damage to the unit.

2.3.2

Line Receptacle Connection

Connect the supplied power cord to the rear panel LINE
receptacle and to a grounded AC power receptacle sup­plying the correct voltage.

WARNING
The Model 3940 is equipped with a 3-wire
power cord that contains a separate ground
wire and is designed to be used with
grounded outlets. When proper connections
are made, instrument chassis is connected to
the power line ground. If the AC outlet is not

rounded, the rear panel ground terminal

L must be connected to safety earth

b

ground using #18AWG (or larger) wire be­fore use.

2.3 LINE VOLTAGE SUPPLY

The Model 3940 operates with a lOOV, lZOV, 22OV, or
240V flO%, 48 to 62Hz, single-phase AC power supply.
The power consumption is 84VA.

2.3.1

The LINE VOLTAGE SELECTOR switch on the rear
panel allows you to change operating voltage of the
power supply. The standard setting of the switch is the
same as the voltage available in the country to which the
unit is shipped.

To change the power supply voltage, first disconnect the
line cord, and set the supply voltage switch in the correct
position. Wait at least five seconds before turning the
power back on after turning it off.

2-2

Line Voltage Selector Switch

2.3.3

Line Fuse

The line fuse, which is integral with the power line recep­tacle, protects the instrument from over-current situ­ations. To replace the fuse, first disconnect the line cord,
then pry out the fuse compartment (immediately to the
left of the FUSE marking) with a small screwdriver. A
spare fuse is located in the compartment with the fuse be­ing used. Replace the blown fuse only with the type listed
in Table 2-1, then close the compartment.

WARNING
Disconnect the line cord from the instru­ment before replacing the fuse.

CAUTION
Use only a fuse of the rating listed in
Table 2-1, or instrument damage may occur.

SECTION2

Geffitw Sfarfed

Table

2-l.

Fuse Replacement

2.4 HANDLING PRECAUTIONS

A flat keyboard coated with a polyester film forms the
control panel surface of the Model 3940. Be careful not to

damage the keyboard surface by cutting it with a sharp

instrument or touching it with a hot object.

When the panel or case becomes dirty, clean it with a soft
cloth. If the panel or case is too dirty for cleaning with a
dry cloth, dampen the cloth in mild detergent, and wipe

the panel or case with the damp clothNever use solvents
such as thinner or benzene, or chemical dust cloths to
avoid damaging case or front panel surfaces.

2.5 BASIC OPERATION

The following paragraphs summarize front panel operat-

ing controls, give typical test connections, and discuss
typical operating examples for the Model 3940.

2.5.1

Figure 2-l summarizes each front panel feature. For de­tailed information on each operating feature, refer to Sec­tion 3.

Front Panel Summary

2.5.2 Typical Test Connections

Figure 2-2 shows typical tests connections between the
Model 3940 main synthesizer and a DUT (sub synthesizer

connections are essentially the same). Note that 5OQ char­acteristic impedance cables such as the Model 7051

should be used for all signal connections.

2-3

SECTION 2

Gettinf Started

SUB SYNTHESIZER OUTPUTS

SYNC OUT: TTL Sync signal

FCTN OUT: Analop output

r

SPACE: Selects number of

at programmed
frequency

GPIB: Prcqwns address

and terminator

Adds shifted function

to scme other keys

Allows sub synthesizer

TRIG

MAN: Manually trf~rs unit

MARK: Selects number of

cscillatlon cycles
stql cycles

RCL: Recalls setups

I

I

FREQ: Sets frequency

AMPTD: Sets output amplitude

OFFSET: Sets DC offset (main only)

FCTN: Sets waveform type

MODE: Sets operating mode

L

START FREQ. Programs start frequency

STOP FREQ. Prcgrams stop frequency

CTR 4: Transfers marker to centa

SPAN: Sets span frequency

SWEEP FCTN: Sets function
SWEEP TIME: Sets time

START: Sixk single or

SWEEP OFF: Cancels sweep mode

STATE: Sets sweep starV

HOLD/FtESM: Pauses/resumes sweep

DATA

04, r Enters numeric

data

RUB OUT: Deletes current

number

ENTRY

(main crab)
(main crab)

(main and sub)
(main only)

SWEEP

cm sets center frequency

MKR: Sets marker frequency

SWEEP OPR

continuous sweep

stop state

MAIN SYNTHESIZER OUTPUTS

FCTN OUT: Analog waveform

I

I

OSPL

Rehlrns display

to namsl

Figure 2-l.

2-4

Front Panel Summary

SECTION 2

Getting Started

Model 3940

Main

Function

output

Figure 2-2. TypicaI Test Connections

2.5.3

Operating Examples

The following examples give step-by-step instructions

for setting basic Model 3940 operating parameters. All

examples except for Example 7 describe

main

synthesizer
operation. Sub synthesizer operation for frequency, am­plitude, and function is similar to main synthesizer op­eration. Offset, mode, and sweep parameters do not ap­ply to the sub synthesizer.

Example I: Selecting the Waveform Type (Function)

The waveform type can be selected using the FCTN key
as follows:

1. Press FCTN and note that the instrument displays
the current function and the available functions.

2. Press the number key corresponding to the desired
function (O-61, or rotate the MODIFY knob until the
desired function number is displayed. For example,
press 3 to choose select the square wave function.
The waveform will immediately change to the se­lected function.

3. Press DSPL to return to the normal display mode.

Example 2: Setting the Waveform Frequency or Period

Use FREQ to set the frequency or period of the output
waveform as follows:

1. Press FREQ to enter the frequency programming
mode. The instrument will display the allowable fre­quency range for the selected waveform.

I

(Model 7051)

2. To directly enter a completely new numeric fre­quency value, key in the desired number followed
by the appropriate units key (Hz, kHz, or MHz). For
example, to enter a frequency of lO.lkHz, press: 1
O.lkHz.

3. To simply modify an existing frequency value, place
the cursor on the digit to be changed using 4 or b,
then use the MODIFY knob to set the digit to the de­sired value. Repeat as necessary for all digits to be
changed. Note that you can press the STEP SIZE key
to multiply or divide by 2 or by 10.

4. To display the time period of the waveform fre­quency, press the set key. You can then key in a new
time period or modify the existing period, if desired.

5. Press Hz, kHz, or MHz to return to frequency dis­play.

6. Press DSPL to return to normal display.

Example 3: Setting the Output Amplitude

Use the AMMD key to set the output voltage amplitude
as follows:

1. Press AM??TD, and note that the instrument displays
the current amplitude and allowed amplitude range.

2. To enter a completely new amplitude value in p-p
units, key in the numeric value, then press V or mV,
as required. For example, to enter a 30mV p-p ampli­tude, press: 3 0 mV.

3. To simply modify the existing amplitude value, use
the cursor keys and the MODIFY knob to set the
value as required.

4. kess DSPL to return to normal display.

2-5

SECTION 2

Getfing Started

Example 4: Programming the DC Offset

The OFFSET key allows you to set the DC or average level
of the main synthesizer output waveform, as in the fol­lowing example:

1.

Press OFFSET and note that the instrument displays
the current offset value and allowed range.

2.

Either key in the desired offset, or use the MODIFY
knob and cursor keys to change the value.
Press DSPL to return to normal display.

3.

Example 5: Selecting the Operating Mode

The Model 3940 main synthesizer can be operated in con­tinuous, burst, trigger, or gate modes. The operating
mode can be set with the MODE key as in the following
example:

Press MODE and note that the instrument displays

1.
the current mode and available modes (continuous,

burst, trigger, and gate).

2. Press the number of the desired mode (or rotate

MODIFY to choose the desired operating mode).
Press DSPL to return to normal display.

3.

Example 6: Controlling Sweep Operation

2.

Press STOP FREQ and set the sweep stop frequency
as desired. For example, to program a 1OkHz stop
frequency, press 10 kII2.

3.

Press CTR and SPAN to view the center and span
frequencies. With 1kHz and 1OkHz start and stop
frequencies, the center and span frequencies wilI be

5.5kHz and 9kHz respectively. NOTE: If you change
the center or span frequencies, the start and stop fre­quencies will be automatically changed accordingly.

4.

Press SWEEP FCTN, and choose the type of sweep.
For example, press 2 to select a linear, ascending
sweep type.

5.

Press SWEEP TIME, and program the sweep time as
required. For example, press 5 set to program a five­second sweep time.

6.

To generate a single sweep, press SINGL START.
The unit will generate one sweep based on selected

sweep parameters.

7.

To generate continuous sweeps, press SHIFT START

CONT. The Model 3940 will generate sweeps con­tinuously based on selected sweep parameters.

8.

Press SWEEP OFF to stop a sweep.

Example 7: Using the Sub Synthesizer

Sub synthesizer parameters can be programmed in the
same way as the equivalent main synthesizer. The steps
below demonstrate how to program the sub synthesizer
function, frequency, and amplitude.

The Model 3940 main synthesizer can be used to sweep

across a desired frequency range. The SWEEP keys allow
you to program sweep parameters, while the SWEEP
OPR keys control sweep operation. Perform the steps be­low to demonstrate basic sweep operation:

Press START FREQ, and key in or use MODIFY to set

1.
the sweep start frequency. For example, press 1 kHz
to program a 1kHz start frequency.

1. To program the sub synthesizer function, press SUB
FCTN, then choose the desired waveform.

2. Program the sub synthesizer frequency by pressing
SUB FREQ, then key in or modify the frequency, as
required.

3. To set the sub synthesizer output amplitude, press
SUB AMPTD, then set the amplitude as needed

4. Press SUB DSPL to display sub synthesizer parame­ters.

2-6

SECTION 3

Operation

3.1 INTRODUCTION

This section contains detailed information on front panel
operation of the Model 3940. For detailed GPIB (IEEE-488
bus) operation, refer to Section 4.

3.2

3.2.1

The front panel of the Model 3940 is shown in Figure 3-1.
The front panel is made up of a two-line, 40-character liq­uid crystal display and a control panel with a built-in flat
keyboard. The liquid crystal display presents informa­tion useful for the operation of the Model 3940, such as

FRONT PANEL AND REAR PANEL
DESCRIPTION

Front Panel Description

the value of each parameter and the range of permissible
parameter values.

The keyboard includes a SHIFT key, which gives certain

other keys secondary functions. A key which is shaded
with the same color as the SHIFT key requires that you
press SHIFT first before accessing the function of that
particular key.

The keyboard also includes the SUB key, which allows
you to control sub synthesizer parameters. Pressing SUB
followed by FREQ, for example, allows you to set the fre­quency of the sub synthesizer.

Most settings are maintained in battery backed-up mem­ory. As a result, the Model 3940 automatically assumes
the previous settings when the power is first turned on.

3-1

SECTION 3

Operation

SYNTHESIZER

V3-1. Front Panel

Key Representations

This section uses special representation such as [SHIFT],

[SUB], LMODIFYI, or [SIZE] in the explanation of certain
keys. This representation indicates the following:

EmI

Press the applicable key after press­ing the SHIFI key to access the
shifted key function. The liquid crys­tal display indicates “SHIFT” in the
upper left comer when the Model
3940 is in the shift mode.

wJa

Press the applicable key after press­ing the SUB key to put the Model
3940 in the sub mode, which allows
you to set sub synthesizer parame­ters. The liquid crystal display indi­cates “SUB” in the upper left comer

when the Model 3940 is in the sub
mode.

[MODIMI

Either key in the value using the
DATA keys or change a given setting
value with the MODIFY knob. The
up/down step size when increment­ing or decrementing a value is fixed
at 1, and the cursor position is also
fixed.

[MODIFYI [SIZE] Either key in the value using the

DATA keys or change a given setting
value with the MODIFY knob. You
can specify the digit to be modified
by placing the cursor on the desired
digit using 4 orb. In addition, you
can change the modify up/down in­crement using the STEP SIZE key.

3-2

SECTION3

Otlerafion

Detailed Descriptions
Each front panel feature is described below. The circled

number to the left of each description corresponds to the
appropriate number shown in Figure 3-l.

1

POWER ON/OFF

0

POWER controls AC power to the Model 3940.
Press this switch once to turn power on, and press
POWER a second time to turn power off.

2

Display

0

The two-line, 40-character display shows parame­ter values and other important information during
operation. An active display also indicates that in­strument power is turned on.

3

TRIG (Trigger keys for burst, trigger, orgate oscil-

0

la tion)

The various TRIG keys are used during burst, trig­ger, or gate oscillation. The trigger mode can be se­lected using the MODE key described below.

MAN (Manual trigger)
Press MAN to manually trigger the unit. In the

trigger oscillation mode, the trigger signal is gen­erated each time this key is pressed. In the gate os­cillation mode, the gate signal remains on as long
as MAN is pressed.

To use only the manual trigger as the trigger sig­nal, select EXT (external) p for the trigger source,
and disconnect the cable from the EXT TRIG IN
BNC connector.

(Power switch)

In the gate oscillation mode,?lL and 5 correspond
to gate on at falling edge and gate on at rising edge,
respectively.

STOP LEVEL

EmI, [MODal

The STOP LEVEL key allows you to select the out­put level during the stop cycle for the burst oscilla­tion, trigger oscillation, and gate oscillation modes

(the stop level does not apply to the continuous
mode). You can select HOLD or RESET: with
HOLD the waveform will stop at the oscillation
start phase; with RESET, the waveform wrll stop at
the waveform center value.

When the oscillation mode is set to other than the
CONT mode, and the stop level is set to RESET,
the upper frequency limit is restricted to 1MHz.

MARK (Oscillafion cycle)

MODIFY] l%=l
The MARK key allows you to set the number of os-

cillation cycles for the burst oscillation and trigger
oscillation modes.

In the burst oscillation mode, oscillations will be
generated for the number of cycles programmed
with the MARK key, after which oscillations will
be stopped for the number of cycles programmed
with the SPACE key (see below). This on-off cycle
of oscillations will be repeated continuously.

In the trigger oscillation mode, oscillations will be
generated for the programmed number of cycles
only when a trigger is applied. The permitted
range of mark oscillation cycles is from 0.5 cycle to
32,768 cycles, and the resolution is 0.5 cycle.

SOURCE {Trigger source)
[MODIFY]

This key allows you to select the trigger source,

which includes EXT/INT (external/internal) and
I/& (falling edge/rising edge). Selecting EXT
will enable front panel triggering through the EXT
TRIG IN BNC connector. Selecting INT will enable

the internal trigger signal synchronized with the
sub synthesizer output. Note that the front panel
MAN key is operational for both internal and ex-

ternal trigger sources.

SPACE (Stop cycle)

MODa E=JY

The SPACE key allows programming of the num­ber of stop cycles for the burst oscillation mode. In
the burst oscillation mode, oscillations will be gen­erated for the number of cycles set with the MARK
key, and the off or stop period will occur for the
number of cycles set with the SPACE key. This on­off cycle of oscillations will be repeated continu­ously.

The permissible range of settings is from 0.5 cycle
to 32,768 cycles with 0.5 cycle resolution.

3-3

SECTION 3

Operation

PHASE @fart/stop phase)
[MODIFY] [SIZE]

The PHASE key allows programming of the start/
stop phase setting for the burst or gate oscillation
modes. The allowed phase range is from-360.0” to

360.0".

This phase parameter can also be used as a resume
phase for oscillation when using phase sync.

(SUE3) PHASE CSub Synthesizer Phase)
[SUB], [MODIFYI [SIZE]

Pressing [SUB] Pl&4SE allows you to set the phase
of the sub synthesizer output signal. The allowed
phase range is from -360.0” to 360.0”. The synthe­sizer phase can also be used to synchronize phases
with the sub synthesizer when using phase sync.

4 SYNC (Phase sync)
[SHIFT]

ENTRY keys 5 for information on frequency
and period setting.

START FREQ (Start fiequency~

0

[MODIW l-SIZE1

The START FREQ key allows you to set the start
frequency of the frequency sweep. You can specify
a start frequency that is either higher or lower than
the stop frequency. The relationship between the
start and stop frequency values determines the
sweep direction. If the start frequency is higher
than the stop frequency, the sweep will be per­formed in a descending direction. If the start fre­quency is lower than the stop frequency, the
sweep will be performed in the ascending direc­tion.

If the start frequency is changed, the sweep range
will be determined by the new start frequency and
the current stop frequency.

4

0

The $ SYNC key is used for the phase sync mode.
When using the main synthesizer and the sub syn-

thesizer for phase sync, oscillation will synchro­nize phases when this key is pressed, or when the
GPIB “SYN” command is given.

When a multiphase oscillator is formed by con­necting two Model 3940s together with an optional
Model 3949 Synchronous Cable, master unit and
slave unit oscillation will both enter the resume
phase when the master unit $ SYNC key is
pressed, or when the GPIB “SYN” command is
sent to the master unit. Pressing the slave unit 4
SYNC key or sending the GPIB “SYN” command
to the slave unit are considered to be invalid op­erations.

SWEEP (Frequency sweep keys)

The various SWEEP keys are used to program
sweep functions such as start and stop frequency,
center and span frequencies, and sweep function
and sweep time. The paragraphs below summa­rize the operation of these keys. Refer to the speci­fications located in Appendix B for details on the
sweep range.

Note that frequency parameters can also be set us­ing waveform period. See the discussion on the

STOP FREQ (Sfop frequency)
[MODIFYI [SIZE]

The STOP FREQ key allows you to set the stop fre­quency of the frequency sweep. You can specify a
stop frequency that is either higher or lower than
the start frequency. If the stop frequency is higher
than the start frequency, the sweep will be per­formed in ascending order. If the stop frequency is
lower than the start frequency, the sweep will be
performed in descending order.

If the stop frequency is changed, the sweep range
will be determined by the new stop frequency and
the current start frequency.

CTR (Cenfer fYequency)

[MODIFY] E=W

The CTR key allows setting of the center frequency
of the frequency sweep. The center frequency is
specified as the center frequency for the linear
scale, and is not the sweep time basis center fre­quency for LOG sweep.

The relationship between the current start and
stop frequency values determines the sweep di­rection. If the center frequency is changed, the
start and stop frequencies will be changed, but the
span frequency will remain constant.

3-4

SECTION3

Ooerafion

CTR 4 (Substitute
quency)
~SHIFTI

The CTR 4 key substitutes the marker frequency
for the center frequency. The sweep direction and
span frequency are affected in the same manner as
when using the center frequency setting. If the
substituted marker frequency is different than the
center frequency, the start and stop frequencies
will change accordingly.,

SPAN (Frequency span)
[MODIFYI [SIZE]

This key allows you to set the frequency span of
the frequency sweep. The relationship between
the start and stop frequency values determines the
sweep direction. If the frequency span is changed,
the start and stop frequencies will be changed so
that the sweep range is determined by the new fre­quency span and the current center frequency,
which will not change.

of

marker frequency for center fre-

SWEEP TIME (Sweep time)

MODIFY] [SIZE1

The SWEEP TIME key allows you to set the sweep
time, which is the time period from the start fre­quency to the stop frequency. The allowed sweep
time range is from 5msec to 9,999sec.

SWEEP OPR (Sweep Operatim)

SlNGL START (Single start: single-sweep sfarf)
This key starts a single sweep. Only one sweep per

key press will be generated.

CONT START (Continuous stark repeated sweep
starf)

[SHIFTI
This key starts repeated sweeps, which will be

generated continuously until halted with the
HOLD or SWEEP OFF keys.

MKR Marker frequency)

[SHIFT], [MODIFY] [SIZE1

This key allows you to set the marker frequency of

the frequency sweep. Note that you can specify
only one marker frequency. While the oscillation
frequency is higher than the programmed marker
frequency during a sweep, the marker output sig-

nal available at the rear panel MKR OUT jack will
be set low. The marker output signal at MKR OUT
will be set high at all other times.

SWEEP FCTN (Sweep funcfion)

MODIFY]
The SWEEP FCTN key allows you to select the

sweep function. Available sweep functions in­clude: step ( I), linear triangular wave and saw-

tooth wave (A or n ), and log triangular wave or
sawtooth wave (A or A).

With the step sweep function, the output fre­quency simply changes between the start fre­quency and stop frequency at intervals deter­mined by the sweep time. With the linear and log
functions, the frequency increases or decreases
linearly or logarithmically, respectively.

SWEEP OFF (Sweep ofi
SWEEP OFF cancels the sweep mode. The oscilla-

tion frequency will remain at the current fre­quency when this key is pressed, and the MKR
OUT, SWEEP :, 1 NC OT-JT, and X DRIVE OUT sig­nals on the rear panel are set to high level, high
level, and OV, respectively.

START STATE (Start stafe: start frequency output)

This key resets the sweep and sets the output fre-

quency to the start frequency.

When START STATE is pressed, the MKR OUT

and SWEEP SYNC OUT signals on the rear panel
are set high. The X DRIVE OUT signal is set to OV

when the start frequency is lower than the stop fre-

quency; the X DRlVE OUT signal is set to 1OV
when the start frequency is higher than the stop
frequency. These signals can be used for scale ad­justments of XY recorders.

STOP STATE (Sfop frequency output)

rsH.IFU
STOP STATE performs the opposite function of

the START STATE key in that it sets the output fre­quency to the stop frequency.

3-5

SECTION 3

When STOP STATE is pressed, the MKR OUT and
SWEEP SYNC OUT signals on the rear panel are
set high. The X DRIVE OUT signal is set to OV
when the start frequency is higher than the stop
frequency; it is set to 1OV when the start frequency
is lower than the stop frequency.

HOLD/RESM (Hold/resume: temporary stop and re­sume)

This key alternately stops and resumes the sweep.
Pressing HOLD/RESM while sweep is in progress

will halt the sweep with the frequency, MKR OUT,
SWEEP SYNC OUT, and X DRIVE OUT signals
present at that time maintained at their present
values. Pressing HOLD/RESM with the sweep
halted resumes the sweep from the existing condi-

iiOnS.

ENTRY

5

0

FREQ (Frequency)
[MODIFY] [SIZE]

The FREQ key allows you to set the output fre­quency of the main synthesizer. The allowed fre­quency range will vary according to the waveform
type, oscillation mode, stop level, and waveform
duty cycle (see the specifications in Appendix B
for details).

In many cases, the instrument will allow you to set
the waveform frequency to a higher value than the
guaranteed specification range. However, the
quality of the waveform will deteriorate if you set
the frequency above the range of guaranteed
specifications for those particular waveform con­ditions. In all cases, however, an absolute upper

maximum setting limit of lMHz, lOMHz, or
25MHz will apply, depending on waveform set­tings.

(Main parameter setting keys)

Upper Frequency: 1MHz

Limits of Period-based Setting Range: l.OOOpsec
to lO,OOO.Osec

For period-based settings, the frequency is set to
the value of the reciprocal that is rounded to the
nearest number below O.lmHz. Therefore, period­based setting will cause significant errors when
the number of digits for the value of the reciprocal
that is rounded is small. For example, values of
either 6,666.67sec or 4,000.Olsec will result in a fre­quency of 0.0002Hz.

If you press FREQ during sweep operation or dur­ing sweep hold, the current frequency will be dis­played, but you will not be able to change the fre­quency.

The phase of the waveform will be continuous
even when the frequency is changed.

(SUB) FREQ (Sub synthesizer frequency)

NJ-H, MODIFY] [==I

Pressing [SUB] FREQ accesses sub synthesizer fre­quency setting. The allowed sub synthesizer fre­quency range is from OHz to lOOkHz, and the al­lowed frequency range is constant regardless of

waveform type or other parameters.
As with the main synthesizer, the sub synthesizer

frequency can be set in either frequency or time pe­riod units. The permitted range of time period
units is from lO.OOOl.tsec to lO,OOO.Osec. For period-

based setting, the frequency is set to the value of

the reciprocal that is rounded to the nearest num-

ber below O.lmHz. Therefore, period-based set-

ting will cause significant errors when the number

of digits for the value of the reciprocal that is
rounded is small. For example, values of either
4,000.OOsec or 2,857.15sec will result in a frequency

of 0.0003Hz.
The phase of the output waveform will be continu-

ous even when the frequency is changed.

The oscillation frequency can be programmed in
frequency units or time period units. The upper
limit frequency for period-based setting of the per­missible range is as follows:

Upper Frequency: 25MHz

Limits of Period-based Setting Range: 0.04Oltsec
to lO,OOO.Osec

Upper Frequency: 1OMHz

Limits of Period-based Setting Range: O.lOOpec
to lO,OOO.Osec

3-6

AMPTD (Amplifude)

[MODIFY] [SIZE]
Pressing AMPTD allows you to set the output am-

plitude of the unit. The allowed amplitude ranges
from 2.OOmV p-p/no load to 2O.OV p-p/no load
when the DC offset is OV. In other cases, the upper
and lower limits are restricted to the range speci­fied in Table B-4 (Appendix B). The values for the
amplitude setting are for no-load output condi­tions. The unit can be set to display either the no­load or 5OQ amplitude value (see below).

SECTION 3

Operation

The amplitude setting can be specified using
either p-p, rms, dBV, or dBm units. (Note, how-

ever, that dBm units can be used only when a 5052
load is specified). You can specify the appropriate
units by pressing the appropriate ENTER units
key when entering the amplitude. Use mV or V for
p-p values, mVrms or Vrms for rms values, or dBm
or dBVB for dB values.

Note that p-p values are the only permissible units
for DC or arbitrary waveforms, and that the p-p
value varies from one waveform to another if you
specify the amplitude as an rms or dBV value. Also
note that the amplitude set by the AMPTD key is
the amplitude of an AC waveform. Set the ampli-

tude of a DC waveform type with the OFFSET key.

(AMPTD) (Amplitude dispZay selector)

[SHIFI’l

Pressing SHIFT AMPTD toggles the unit between
displaying the no-load amplitude and the 5OQ am­plitude while setting the main synthesizer ampli­tude. Each time this key sequence is performed,

the display will toggle between no-load and 5OQ
amplitude values.

Since the output impedance of the Model 3940 is
5OQ, the amplitude display with 5OQ loads (with
identical outputs) will correspond to half of the
no-load display value (-6dB).

OFFSET (DC offset)

[MODIFY] [SIzEI

The OFFSET key enables DC offset voltage pro­gramming. The allowed offset is between -lOV/
no load and lOV/no load for a DC waveform. For
other waveform types, the offset range is restricted
to the values specified in Table B-4 (Appendix B).
All specified offset ranges are for no-load condi­tions.

(OFFSET) DC oflsef display selector)

[s=l

Pressing SHIFT OFFSET toggles the offset display
units between the no-load value and the 5OQ
value. Each time this key is pressed, the offset
value display will toggle to the opposite type.

Since the output impedance of the Model 3940 is
SOSZ, the 5OSJ DC offset display will correspond to
half of the no load display value for identical out­puts.

FCTN (Function: waveform)
[MODIFY]

This key allows you to choose the output
waveform of the main synthesizer. Available

waveforms include: DC, SIN (sine wave),
angular wave), k (square wave>, n (ascending
sawtooth wave),\ (descending sawtooth wave),

and ARB (arbitrary wave programmed over the
GPIB).

2/ (tri-

(SUB) AMPTD (Sub synthesizer ampIifude)

MJH, &fODIFYl [SEE1

Pressing SUB AMM’D allows you to set the sub
synthesizer output amplitude.

The allowed sub synthesizer amplitude ranges
from 0.2V p-p/no load to 2O.OV p-p/no load. The
sub synthesizer amplitude setting vahtie is the no­load value (5OQ display values are not available
with the sub synthesizer).

Amplitude values can be entered using p-p, rms,
or dBV units. Use V or mV for p-p units, Vrms or
mVrms for rms units, and, of course, dBV for dBV
units. Note that the p-p value may vary depending
on the waveform when using rms and dBV ampli­tude units.

If the waveform setting is DC or ARB, only p-p am­plitude values can be set.

(SUB) FCTN (Sub Synhesizer Funcfion: Sub synfhe­sizer waveform)

NJ-N, [MODa

Pressing SUB FCTN accesses sub synthesizer
waveform programming. Available sub synthe-

sizer waveforms include: SIN (sine wave),
angle wave), k (square wave), n (ascending
sawtooth wave),\ (descending sawtooth wave).

If the waveform setting is changed, the amplitude
setting value is changed automatically to the p-p
value, and the new waveform is output with the
same p-p amplitude.

Qli-

3-7

SECTION 3
Operation

MODE

MODIFY]

The MODE key programs the oscillation mode set-

ting. Available oscillation modes include: CONT

(continuous oscillation), BRST (burst oscillation),
TRIG (trigger oscillation), and GATE (gate oscilla­tion).

6

DATA

0

The DATA key set consists of numeric keys for en-

tering a value and ENTER (units) keys for setting
the units of the entered value. The “.” (decimal
point) key and the +/- (sign inversion) key do not
affect parameters for which they have no function.

Parameters that are selected with one numeric
character, such as waveform and oscillation mode,
do not require that any ENTER key be pressed.
Such parameters are set simply by entering one
numeric character (or by rotating the MODIFY
knob as required).

(Oscillation mode)

OVumeric keys for parameter enty)

7

0

MODIFY

In addition to using the numeric keys, you can set
any parameter except the GPIB address, delimiter,
and memory number by using the MODIFY knob.
The MODIFY knob is operational when the Model
3940 is in the appropriate parameter-entry mode,
and the unit displays the current parameter value.

MODIFY (Modify knob)
When the step size is fl, you can select the digit to

increase or decrease by 1 by placin
der the appropriate digit (use 4 or
the MODIFY knob to the right or left.

When the step size is x+2, you can divide the se­lected parameter by 2 by turning knob counter­clockwise, or multiply the parameter by 2 by turn­ing the knob clockwise. Similarly, when the step
size is x+10, you can divide or multiply the pa­rameter by 10 by rotating the knob counter-clock­wise or clockwise respectively. Note that the cur­sor will not be displayed when the step size is x+2
or x+10.

(Modify operation knob)

%

the cursor un-

) and turning

For other parameters, enter the required value
with the numeric keys, then press the appropriate
ENTER units key. If you enter the incorrect value,
press the RTJB OUT (delete) key. RTJB OUT deletes
the numeric character or decimal point from the
rightmost position. To delete the entire entered
value and return the display to the current value,
press the original function key to enable parame­ter entry for that function.

Pressing any of the ENTER keys will enter the val­ues for the MARK and SPACE waveform cycles
and phase parameters where only one type of unit
is used, or for the GPIB address in which case pa­rameters contain no units.

For frequency and amplitude where parameters
can be entered in different types of units, select the
appropriate units key from the ENTER key to com­plete entry of the value.

The units keys also have a units conversion ftmc­tion. This feature is available for unit conversions
such as frequency-to-period conversion for fre­quency, as well as amplitude p-p/rms/dBV/dBm
conversions. When the units key of the unit to be
changed is pressed with the current setting dis­played, the display will be changed to reflect the
newly selected units; note, however, that the ac­tual outout remains unchanged.

4 Keff cursor)
This key moves the cursor to the left by one digit

each time it is pressed, and it will automatically re­peat left cursor movement as long as it is held
down.

F (Right cursor)
This key moves the cursor to the right by one digit

each time it is pressed, and it will automatically re­peat right cursor movement as long as it is held
down.

S’IXP SIZE (UP/DOWN step size)
STEP SIZE changes the MODIFY knob LB?/

DOWN step size. For parameters with
can be changed using variable step sizes, the step
size will change in the following order each time
this key is pressed: rtl x+2 x+10 . . .

8

Miscellaneous Keys

0

1 - LOCAL (Refurn fo local)
LOCAL cancels remote and returns the instru-

ment to the local mode when used over the GPIB.

values

that

3-8

SECTlON 3

Operation

GME3 (GPIB Address: GPIB address, delimiter)

E3m1

The GLIB key allows you to program the GPIB pri­mary address and the output delimiter used when
the Model 3940 is acting as a GMB talker. Only the
numeric keys can be used for setting these pa­rameters (the MODIFY knob cannot be used). The
allowed range for the primary address is from 0 to
30, and the delimiter can be selected for CR/LF or

CR (CR and LF or CR only).

The GPIB primary address is the integer part of

this parameter, and the delimiter is defined by the

fractional part. For example, a parameter of 2.0 in-

dicates a primary address of 2 and defines CR/LF

as the delimiter. Similarly, a parameter of 4.1 indi­cates a primary address of 4 with CR as the delim­iter.

To change only the primary address, enter only

the integer part of the number; the delimiter will
remain unchanged. To change only the delimiter,
enter the decimal point followed by the fraction (0
or 1); the primary address value will remain un­changed.

C (Beep sound)

W3IET1, bfODIMI

This key controls the beep that sounds when you
press front panel keys and when errors occur. You
can turn the beep OFF (0) or ON (1).

k DUTY (Square-wave duty cycle)

FrODIFyl [SJZH

The n DUTY key allows you to program the
square-wave duty cycle. The allowed duty cycle
ranges from 5.0% to 95.0%.

Two duty-cycle modes are available: 50% fixed
and variable. In the variable mode, the upper fre­quency limit is restricted to 1MHz even if the duty
cycle is set at 50%.

FXD50 (Fixed 50% duty cycle)

rsHJ=1

This key fixes the square-wave duty cycle at 50%.

SHIFT

When programming the primary address and/or

delimiter, remember that you must press any one
of the ENTER keys to complete the entry process.

CAL (Calibration: Main synthesizer output calibra­tion)

CAL performs front panel calibration, which cor­rects main synthesizer AC amplitude and offset
errors. Calibration takes slightly more than 10 sec­onds to complete.

During the calibration procedure, the front panel
display will indicate that calibration is in progress
(the number of asterisks displayed will decrease as
calibration progresses). The main synthesizer
FCTN OUT signal will be turned off, and the main
synthesizer SYNC OUT signal will be un­synchronized while calibration is being per­formed.

To cancel calibration while the procedure is in pro­gress, press the CAL key a second time. To cancel
calibration operations over the GPIB, send ,the
“CAB” command. Other key operations and GMB
commands will not be recognized during calibra­tion operations (except for GPIB inquiry com­mands which will be recognized).

The SHIFT key adds a secondary function to many
other front panel keys. Those keys that have
shifted functions have those functions repre­sented on the lower part of each key using the
same color as the SHIFT key. Keys with shifted
functions include STOP LEVEL, MKR, GPIB, and
FXD50.

The SHIFI key is also used to choose between no­load and 5OQ display modes for the main synthe­sizer amplitude and offset settings. See descrip-

tions under 5
When the SHIFT key is first pressed, the unit en-

ters the shift mode, and the liquid crystal display
indicates “SHIFT” in the upper left corner. The
shift mode is canceled when any key including the
SHIFT key is pressed (if a key with a shift function
is pressed, the unit enters that mode; otherwise, it
returns to the mode it was in before SHIFT was
pressed).

SUB (Sub synthesizer mode)
The SUB key allows access, to the following sub

synthesizer parameter settings: FREQ, AMPTD,
FCTN, and PHASE. In order to program any of
these four sub synthesizer parameters, press the
SUB key followed by appropriate key. When the

for more details.

0

3-9

SECTION 3

Operation

instrument enters the sub synthesizer mode, the
liquid crystal display indicates “SUB” in the upper
left corner. The sub mode is cancelled when any
key except for the four sub synthesizer keys out­lined above is pressed.

The main parameters of the sub synthesizer can be
displayed by pressing SUB DSPL.

MEMORY (Memory operation keys)

9

0

The MEMORY keys allow you to store and recall

instrument setups. Ten units of memory, num-

bered 0 through 9, are available for setup storage.

ST0 (Store: store setup in memo y1

The ST0 key stores the current instrument setup

parameters in the selected memory location (O-9).
You can use only numeric keys to store setups (the
MODIFY knob cannot be used). Pressing the nu­meric key will immediately store the current pa­rameter values and erase the previous setup in the
selected memory location.

RCL (Recall: read setup from memo yJ
RCL reads instrument setups from the desired

memory location (O-9). You can use only numeric
keys for selecting memory locations to recall (the

MODIFY knob cannot be used). Pressing the nu-

meric key will immediately read the contents of
the selected memory location and will change the
current instrument settings accordingly.

even when the lock is ON. However, you cannot
return the instrument to local with the LOCAL key
when the GPIB LLO (Local Lockout) command is
in effect.

Current parameter values such as frequency can
be displayed by pressing appropriate keys when
the lock is ON. The liquid crystal display will indi­cate ‘LOCK” in the position where the modifica­tion step size is normally indicated. Also, parame-

ter names will not flash, and the cursor will not be
displayed.

PRST Wrese

t)

[f=.Im

The PRST key recalls the factory default preset op­erating parameters. Refer to the specifications in
Appendix B for a summary of preset parameter
settings.

DSPL (Display: Main synthesizer main parameter dis­play)

DSPL displays the following main synthesizer
main parameters simultaneously: Signal output
ON/OFF (blank for ON), frequency, amplitude,
DC offset, waveform, oscillation mode, and sweep
mode (blank for normal oscillation). Note that pa­rameters cannot be programmed from the main
parameter display; you must press the appropri­ate keys before setting parameters.

(SUB) DSPL (Sub Synthesizer Display: Sub synthe­sizer main parameter display)

WBI

Additional

10

0

LOCK Eock out front panel keys)
This key allows you to disable most front panel

keys. Available modes are ON (1) and OFF (0).
When the lock is ON, most front panel keys are

disabled, and the corresponding operating modes

cannot be changed. However, both LOCK and
FCTN OUT ON/OFF are still operational when
the lock is ON. In addition, trigger input and
sweep control input from appropriate BNC con­nectors are also enabled.

Lock ON/OFF can also be programmed over the

GPIB with the “LCK“ command, and GPIB pro-

gramming is not disabled when the lock is on. You

can return the unit to local with the LOCAL key

3-10

Keys and Connectors

Pressing SUB DSPL displays the following sub
synthesizer main parameters simultaneously: Sig­nal output ON/OFF
amplitude, waveform, and phase. Sub synthesizer
parameters cannot be programmed from the sub
synthesizer main parameter display.

FCTN OUT ON/OFF (Signal output ON/OFF)
FCTN OUT turns both the main and sub synthe-

sizer outputs off or on simultaneously. Each time
this key is pressed, ON/OFF will toggle to the op­posite state.

When FCTN OUT is OFF, the main synthesizer
FCTN OUT signal will be open-circuited, and the
sub synthesizer FCTN OUT signal will be set to
OV. In addition, the main synthesizer SYNC OUT

(blank

for ON), frequency,

signal will be identical to the output during FCTN
OUT ON, but the sub synthesizer SYNC OUT sig­nal will be set to high or low logic levels.

The liquid crystal display will indicate “OFF” in
the upper left corner when the Model 3940 is in the
FCTN OUT OFF mode (except in the SHIFT, SUB
or REMOTE modes).

13

SUB SYNTHESIZER FCTN OUT (Sub synthe-

0

sizer waveform output)

This BNC jack provides the sub synthesizer
waveform output signal. The maximum output
voltage range is rtlOV/no load, and the output im­pedance is 600!2.

SECTION3

Operation

11

0

12

0

Note that the factory default setting for FCTN
OUT is ON at power on.

MAIN SYNTHESIZER FCTN OUT @fain syn­t~~siz~r~wavEforr;zoutlrut}

This BNC jack provides the main synthesizer
waveform output signal. The maximum output
voltage range is rtlOV/no load, and the output im­pedance is 50B

MAIN SYNTHESIZER SYNC OUT (Main syn­thesizer synchronous output)

This BNC jack provides a TTL-level square wave
signal at the same frequency as the main synthe­sizer function output waveform. The output im­pedance is approximately 5OQ and it can be use
with 5OQ terminations.

14

SUB SYNTHESIZER SYNC OUT (Sub synthe-

0

sizer synchronous output)

This BNC jack is the sub synthesizer synchronous
output, which outputs a TTL-level square wave
signal at the sub synthesizer output frequency.

15

EXT TRIG IN (External-trigger input)

0

This BNC connector is an input for external TTL­level signals, which can be used to trigger the
Model 3940.

EXT TRIG IN is internally pulled up to a high logic
level, which means that the external trigger input
will remain high with no input signal connected. If
the EXTJ trigger source is selected with the unit
in the gate oscillation mode, the gate signal will be
enabled, and the unit will effectively be in the con­tinuous i)scillation mode with no external trigger
input signal applied.

3-11

SECTION 3

Operation

III I I /

Figure 3-2.

Rear Panel

I/ -\ I

- // \\

I I

HOLD

IN

I

STARTIN MKR OUT SYNC OUT XDRIVEOUT

WARNING

I III

I III

3.2.2

The following paragraphs describe the various aspects of

the Model 3940 rear panel, which is shown in Figure 3-2.

16

0

3-12

Rear Panel Description

PHASE SYNC I/O (Synchronous operation input1

output)

PHASE SYNC I/O is a 36-pin connector used to
connect two Model 3940s together to form a multi­phase oscillator. The optional Model 3949 Syn­chronous Cable is required to make connections.

i 7 GPIB (General Purpose Interface Bus connector)

0

This connector is the 24-pin connector used to con­nect the Model 3940 to the GPIB (IEEE-488 bus).
Shielded GPIB cables, such as the Model 7007, are
recommended for bus connections.

18 EXT ADD IN (External add input)

0

This BNC connector is designed for applying ex­ternal waveforms. The inuut imuedance is au­proximately 1OOkQ. Sign& appli;d to this inpk
will be added to the main synthesizer waveform
and subsequently output. See the specifications in
Appendix B for more details on the external add
input.

SECTION3

Operation

(SWEEP) HOLD IN (Sweep hold input)

19

0

This

BNC connector accepts a
used for sweep hold input. The sweep is halted as
long as the input signal is at a low logic level.

(SWEEP) SINGL START IN (Single-sweep start

20

0

0

0

input)

This BNC connector accepts a TTL-level signal
used to start a single sweep. A single sweep starts

at the falling edge of the input signal.

21

(SWEEP) MKR OUT (Sweep marker output)

This BNC connector provides a TT’L-level signal

used for sweep marker output. This signal goes
low when the frequency rises above the marker
frequency during a sweep, and it remains high at
all other times.

22

(SWEEP) SYNC OUT (Sweep synchronous out-

put)

This BNC connector provides a TI’L-level signal
for sweep synchronous output. This signal is at
low level while a sweep from the start frequency to
the stop frequency is in progress; it is at a high
level at all other times.

‘ITL-level signal

cleaned at least once every three months in a clean
environment, or at least once a month in a dirty en­vironment.

CAUTION
Immediately turn off the power to the
unit if the fanceases to operate. Be careful
not to obstruct the exhaust ports on the
upper and lower panels. Failure to ob-

serve these precautions may result in in­strument damage.

25 LINE VOLTAGE SELECTOR (Supply voltage

0

switch)

This switch sets the Model 3940 for the correct line
voltage. Using a flat-blade screwdriver, set the
switch in the proper position for the supply volt­age in your area.

WARNING
Disconnect the line cord before changing
setting the switch position.

CAUTION
Operation the Model 3940 on an incorrect
line voltage may result in instrument dam­age.

23

0

0

(SWEEP) X DRIVE OUT (Sweep X-axis drive out-

put)

This BNC connector provides the signal for sweep
X-axis drive output. The output voltage ranges
from OV to lOV, and it increases and decreases ac­cording to the sweep direction as the sweep is gen­erated. This output signal is intended for use as the
X-axis drive for an oscilloscope or XY recorder.

24

Air intake port
An air intake port is provided on the rear panel for

cooling. Allow at least four inches of clearance be­hind the port when installing against a wall.

When the air filter becomes dirty, remove it by

pulling the air filter cover, and clean the filter with
pressurized air or wash it with a mild detergent.

Make sure that the filter is completely dry before

installing it back in the unit. The filter should be

(Grounding terminal)

The grounding terminal is connected to the chassis

of the Model 3940. To prevent interference and for
safety, be sure to ground this terminal.

WARNING
If the Model 3940 is connected to an un­grounded AC outlet, connect the grounding
terminal to safety earth ground using
#18AWG minimum wire before use.

27

LINE (Power input connector), FUSE

0

The LINE connector is used to connect the instru­ment to AC power.

WARNING
To avoid the possibility of electric shock,
connect the Model 3940 to a grounded AC
outlet.

3-13

SECTION 3

Operiztion

The fuse holder is located below the LINE connec­tor. The fuse can be replaced by disconnecting the
line cord and prying out the fuse holder. Replace
only with the type indicated below.

Fuse Current

Line Voltage Rating
llOV, 120v 2A

22OV, 240V

NOTE: fuses are 5 x 2Omm and
have 25OV, normal blow ratings.

IA

3.3 Input and Output Connections

3.3.1

Input Connections

EXT TRIG IN
(SWEEP) SINGL START IN
(SWEEP) HOLD IN

1 Figure 3-3.

Logic Input Circuifs

sizer output signal. Important specifications are summa­rized below.

Four signals are applied to the BNC connectors of the
Model 3940. The specifications of the input signals are
given below.

CAUTION
Be careful not to exceed the maximum allow­able input voltages, or instrument damage
may occur.

Logic Inputs

Logic inputs include EXT TRIG IN (external trigger in­put), SWEEP SINGL START IN (single-sweep start in­put), and SWEEP HOLD IN (sweep hold input). Key
specifications for these inputs include:

Input voltage: TTL level
Allowable maximum input voltage: OV to +5V
Circuit: See Figure 3-3, Logic Input Circuits.

Analog Input

The EXT ADD INPUT jack can be used to apply an exter­nal analog signal which is then added to the main synthe-

Input voltage range: Max. flOV (variable according to
AC amplitude, DC offset, and waveform settings)

Allowable maximum input voltage: rtl5V
Input frequency range: DC to 1MHz
Input impedance: Approximately 1OOkQ (1OlkQ)
Circuit: See Figure 3-4, Analog Input Circuit

I Fiwre 3-4. halo!z Invut Circuit

3-14

SECTION 3

Operation

3.3.2

Output Connections

Six output signals are available from various BNC con­nectors of the Model 3940. The specifications for the out-

put signals are given below.

CAUTION
Be carefulnot to connect an external signal to
an output connector, or instrument damage
may occur.

Logic Outputs

Logic outputs include the MAIN SYNTHESIZER SYNC
OLJT (main synthesizer synchronous output), SUB SYN-

THESIZER SYNC OUT, sub synthesizer synchronous

output), SWEEP MKR OUT., (sweep marker output), and
SWEEP SYNC OUT (sweep synchronous output. Specifi­cations for these outputs are summarized below.

Output voltage: TTL level Circuits: See Figure 3-5,

Figure 3-6, and Figure 3-7

Figure 3-5.

(Main

Synthesizer)

SYNC OUT

1OpF

Main Synfhesizer Sync Output

SYNC OUT

Analog Outputs

MAIN SYNTHESIZER FCTN OUT

(Main Synthesizer Waveform Output)
Maximum output voltage: +lOV/no load, &5V/50!2
load
Output impedance: 5OQ
Recommended load impedance: 5052 or more

SUB SYNTHESIZER FCTN OUT

(Sub Synthesizer Waveform

Output)

Maximum output voltage: rtlOV/no load
Output impedance: 6OOQ
Recommended load impedance: lOk,Q or more

SWEEP X DRIVE OUT

(Sweep X Axis Drive Output)
Output voltage: OV to +lOV/no load
Output impedance: 6OOQ
Recommended load impedance: 1OkQ or more

l-lOOpF

T

Figure 3-6. Sub Synfhesizer Sync Outpuf

4.7 m (SWEEP) MKR OUT
(SWEEP) SYNC OUT

Fimre 3-7. Sweep Marker and Sync Oufputs

3-15

SECTION 3

Operation

Output Considerations

All logic outputs except for the main synthesizer
waveform synchronous output are driven by a 74LS14

buffer. Be careful not to connect a load that results in ex-

ceeding the drive capability of this TTL IC. Also, do not
use excessively long connecting cables, as the resulting
capacitance may have detrimental effects on the output
signals.

The main synthesizer synchronous output impedance is
matched at approximately 50R. Best waveform quality
will be obtained it susd coaxiai cabies, terminated with a

. .r-^-

5OQ impedance, are used.

The sub synthesizer synchronous output impedance is
matched at approgmately 5OQ at higher frequencies.
Relatively good waveforms will be obtained if 5OQ coax­ial cables are used; however, the cables must not be termi­nated with a 5OQ impedance.

The main synthesizer waveform output impedance is
5OQ To maintain consistent amplitude across the entire
bandwidth, and for maximum square-wave quality, use

a

5OQ coaxial cable for connections, and terminate the op­posite end of the cable with a 5OQ impedance. The actual
output voltage will be displayed by the Model 3940 if the
output amplitude display is set for 5OQ loads.

WARNING
To avoid the possibility of electric shock, use
only grounded AC receptacles for power
connections.

Turn on Model 3940 power by pressing in on the
front panel POWER switch. Power is ON when the
POWER switch button is depressed (in); power is
OFF when the POWER switch button is released

(out). When the power is turned on, the Model 3940
will begin normal operation, and the liquid crystal
display backlight will turn on.

3.

When the power is first turned on, the Model 3940
will return to the previous settings effective prior to
power-off, and the unit will display the main synthe­sizer main parameters.

If the previous settings were not stored correctly, the
error code “Er MEMO 14” will be displayed, and the
preset settings will be placed into effect. At this
point, main synthesizer main parameters will be dis­played, and the settings prior to preceding power­off will be lost. This situation occurs when the
backup battery used to maintain memory has insuf­ficient charge, and stored data cannot be maintained.
A fully-charged battery can retain memory for ap­proximately 60 days. This time period, however,
varies slightly with ambient temperature and from
one battery to another. Approximately 50 hours with
unit power turned on are required to fully charge a
dead battery.

When the battery becomes too weak for practical
use, contact your Keithley representative or the fac-

3.4 STARTUP

1. Check that the supply voltage switch is set to the
proper position for the supply voltage. The allow­able supply voltage range is HO% of the voltage at
which the supply voltage switch is set.

CAUTION

Operating the Model 3940 in an incorrect

line voltage may result in damage to the unit.

tory for information on obtaining a replacement.

4.

The backup battery may be discharged when the
Model 3940 is used for the first time after being pur­chased, or if the unit has not been turned on for a con­siderable length of time. Turn on power for at least
several hours to charge the battery.

5.

Sweep operation mode parameters are not stored
when the power is turned off. Therefore, turning the
power off during sweep operation, sweep hold, end

of single sweep, start frequency output, or stop fre­quency output, will result in a sweep-off state the
next time power is turned on.

2. Make sure that the power is off, then plug the sup­plied power cable firmly into the LINE connector on

In addition, turning the power off during calibration

cancels the calibration process, and calibration op­the rear panel of the Model 3940. Insert the power eration will not automatically restart when power is
plug into a grounded AC power receptacle.

3-16

turned back on.

6.

If the error code “Er MEMO 14” is displayed at
power-on, the main synthesizer amplitude accuracy
may not be within the specified range. In this situ­ation, wait for a few seconds after power-on, then
perform calibration by pressing the CAL key.

7.

If, at power on, the Model 3940 does not enter the
mode with settings that were effective immediately
before previous power-off (or the preset operating
modes), or if the main display does not appear, con­tact your Keithley representative or the factory to de-

termine the correct course of action.

NOTES:

1. Wait for at least five seconds before turning on the
Model 3940 after turning it off.

2. For high-accuracy measurement applications, allow

the Model 3940 to warm up for at least 30 minutes to
allow internal circuits to stabilize.

3.5 OPERATING PROCEDURES

SECTION3

Operation

Key Operation
Press FCTN.

Press 3

Press 2

Parameters that require units, such as frequency, ampli­tude, and phase, can be changed by entering the new
value with the numeric keys and pressing the appropri­ate ENTER key to complete the parameter entry process.
While entering the new value, the current parameter
value, unit display, and modification step size will disap­pear from the display, and the new value will be dis­played. To correct an entered value during the entry
process, press the RUB OUT key, which will delete one

character at the rightmost position of the entered num-

ber. To re-enter the entire parameter value from the be-

ginning, press the same parameter key to return to the
corresponding parameter setting.

Display Result
Currently selected waveform

(<sIN>l) will be displayed.
Waveform changes to c I-L >3

(square wave).

Waveform changes to

(triangle wave).

c

2/ >2

3.51 Setting Parameters Using Numeric
Keys

When the appropriate parameter key such as FREQ,
AMPTD, OFFSET, or PHASE is pressed, the parameter
name and the present parameter value will be indicated
in the upper part of the liquid crystal display. The al­lowed range of the parameter setting and useful help in­formation will appear in the lower part of the liquid crys­tal display.

The parameter value can be changed when the parameter
name indicated in the upper part of the liquid crystal dis­play is flashing. The parameter name will not flash when
the unit is in the GPIB remote mode, or when the front
panel lock is enabled.

Parameters that are selected by pressing one numeric
character (such as waveform, oscillation mode, and tig­ger source>, can be changed simply by pressing the corre­sponding numeric key. An error message will be dis­played if the entered value is outside the allowed range.
Other displays and internal settings remain unchanged
when an error occurs.

For frequency and amplitude, which have several units

options, select and press the appropriate units key to
complete the entry process. For phase and marker fre­quency parameters, which have only single parameter
units, press any one of the ENTER keys to complete en-

try-

Regardless of the number of digits for the entered value
and the size of the units (MHz, kHz, Hz; set, msec, set; V,
mV; or Vrms, mvrms), the predetermined number of
digits, resolution, and units will all be properly adjusted
and displayed. When values below the display resolu­tion are entered with the numeric keys, the value will be
rounded to the nearest whole number and set accord­ingly.

When inappropriate values are entered, an error message
will be displayed and the display will return to the previ-

ous value. Internal settings will remain unchanged when
an error condition occurs.

Example: Changing the waveform type from the current

sme wave) to k (square wave) or to

We
wave).

2/ (triangular

Example: To change frequency from a current value of
1Hz to 2.54Hz. (Correcting an entered value of “2.55”
during entry.)

3-17

SECTION 3

Operation

Key Operation

Display

Press FREQ Currently selected frequency “l.OOOOHz” will be displayed.
Press 2 The value of the key pressed (2) will appear.
Press . The decimal point appears to the right of the 2.
Press 5 The display now shows “2.5”.
Press 5

The display indicates “2.55”.
Press RTJB OTJT The last 5 is deleted, and the display reads “2.5”.
Press 4 The display indicates “2.54”.

3.52

Press Hz

Setting Parameters with MODIFY

Entry is complete, and the display shows “2.54OOHz”

You can change parameter values with the MODIFY
knob and cursor keys in the following cases:

1.

When the name of the parameter to be changed is
blinking in the upper part of the liquid crystal dis­play. (The parameter name indicated in the upper
part of the liquid crystal display will not flash when
the unit is in the GPIB remote, or when the keyboard
lock is on.)

2.

In the situation in step 1, the current value specified
is displayed, and the modification step size is pre­sented in the upper right comer of the liquid crystal
display. (Modification step size will not be displayed
during numeric key input. Modification cannot be
performed during numeric input.)

When the step size is tl, you can specify the digit for UP/
DOWN adjustment by placing the flashing underline
cursor under the appropriate digit with the cursor keys,
and turning the MODIFY knob to the right or left. When
the step size is x+2 or x+10, the cursor will disappear, and
you can multiply or divide by 2 or 10 by turning the
MODIFY knob to the right or left. The step size and the
current cursor position will be stored with the respective
parameters when those parameters are stored in mem-

ory-

Changing a value by modification will never result in an
error because the modification process automatically
limits parameter adjustments to the maximum allowed
range for that particular parameter. MODIFY cannot be
used to store or recall memory locations, or to set the
GPIB address and delimiter; only the numeric keys can

be used to program these operating modes.

For parameters that are selected with one numeric char­acter (such as waveform and oscillation mode), the flash­ing cursor is fixed below the numeric character and can­not be moved. The step size is fixed to +l and cannot be
changed.

For parameters that require units (such as frequency and

amplitude), the step size can be changed by pressing the

STEP SIZE key. It is not necessary to use a units key when

changing the value with the MODIFY knob. When modi-

fying an existing value, the modified value will automati-

cally replace the old parameter value, and the current

units will remain unchanged.

When the step size is indicated in the rightmost position
of the liquid crystal display, the step size will change in
the following order each time the STEP SIZE key is
pressed: +l x+2 x-t-10 +l...

3.5.3 Error Codes

When an error occurs, the Model 3940 displays an error

code in the upper right corner of the liquid crystal dis­play, and the unit generates a~long beep sound (if the
beep sound setting is on). The Model 3940 then displays
the current specified parameter value.

Displayed error codes and their meanings are summa­rized below. The error number at the end of each code
corresponds to the GPIB error code.

Er GPIBOl

l

The Model 3940 received a non-recognizable pro­gramming or inquiry command over the GPIB.

Examples:

“ABC 2”

Non-recognizable programming command
is given.

SECTION3

Operafion

“?ABC”:

Non-recognizable inquiry command is

given.

“123.4”:

l

The Model 3940 received a command that is not recog-

Parameter values are given without headers.

nized in the current mode.

Examples:
Main synthesizer frequency setting command is given

during sweep operation.

Amplitude setting command is given during calibration
operation. (Only the calibration stop command is accept­able during calibration operation.)

l

The Model 3940 received a command string that is be­yond the capacity of the GPIB input buffer.

Er UNIT02

l

You attempted to specify an incorrect parameter unit

Er FREQ03

You attempted to specify a main synthesizer fre­quency setting above 25MJXz.
You attempted to specify a main synthesizer period
setting outside the allowed range of 0.04pec to
10,OOOsec.
You attempted to specify a sweep start, stop, center,
span, or marker frequency or period parameter out­side the allowed range.
You attempted to specify a value that causes the re­sulting start or stop frequency to exceed the allowed
sweep center or span frequency (period)

range.

Example:

You attempted to specify a 15MHz center frequency
when the span frequency is 2OMHz. (You have at-

tempted to specify 5MHz for start frequency and 35MHz

for stop frequency.)

l

You attempted to set the sub synthesizer frequency
higher than 1OOkHz.

* You attempted to specify a sub synthesizer period out-

side the allowed range of 1Opsec to 10,OOOsec

Examples:

You pressed the dBm key while setting the sub synthe­sizer amplitude.

You pressed the Vrms key while setting the offset volt­age.

l

You attempted to select an unacceptable unit for other

Settilp.

Example:

You attempted to specify an amplitude value other than
p-p for a DC or arbitrary waveform type.

Er PHAS04

l

You attempted to specify a phase setting value greater
than &360”.

Er AMPTOS

l

You attempted to specify main synthesizer amplitude
setting outside the range specified in Table 3-l.

l

You attempted to specify a sub synthesizer amplitude
setting outside the range specified in Table 3-2.

Er OFSTOG

You attempted to specify a DC offset value greater than
+lOV/no load or &5V/SOsZ load.

3-19

SECTION 3

Operation

Table 3-l. Main Synthesizer Amplitude Range

Waveforms Amplitude with No Load

%

20.0Vp-p/no load to

2.00mVp-p/no load

7.07Vrms/no load to

0.7lmVrms/no load
ld9dBV/no load to

-63.0dBV/no load

2/

A

u

IL

20.0Vp-p/no load to

2.00mVp-p/no load

5.77Vrms/no load to

0.58mVrms/no load

15.2dBV/no load to

-64.7dBV/no load

20.0Vp-p/no load to

2.00mVp-p/no load
lO.OVrms/ no load to

1 .OOmVrms /no load

20.0dBV/no load to

-bO.OdBV/no load

Amplitude with 5OQ Load

lO.OVp-p/5OQ to l.OOmVp-p/5OQ

3.53Vrm.s/5OQ to 0.36mVrms/5Oa

10.9dBV/50d to -69.0dBv/50SI

23.9dBm/50Q to -56.0dBm/500

lO.OVp-p/5OQ to l.OOmVp-p/5OQ

2.88Vrms/500 to 0.29mVrms/50R

9.2dBV/50Q to -70.7dBV/50Q

22.2dBm/50Q to S7.8dBm/500

lO.OVp-p/5OsZ to l.OOmVp-p/5OQ

5.OOVrms/50 R to 0.50mVrms/50Q

13.9dBV/50a to -66.0dBV/50R

26.9dBm/50Q to -53.0dBm/50Q

Table 3-2. Sub Synthesizer Amplitude Range

Waveforms Amplitude with No Load

2/

20.0Vp-p/no load to 02Vp-p/no load

7.07Vrms/no load to O.lVrms/no load

17.OdBV/no load to -23.0dBV/no load

2/
A
u

n

20.0Vp-p/no load to 0.2Vp-p/no load

5.7Vrms/no load to O.lVrms/no load

15.2dBV/no load to -24.7dBV/no load
IZO.OVp-p/no load to 02Vp-p/no load

lO.OVrms/no load to O.lVrms/no load

20.0dBV/no load to -2O.OdBV/no load

Er ACDC07
With a waveform other than DC and anon-zero DC offset

(in other words, the DC offset was to be added to the AC

waveform), you attempted to specify an invalid ampli-

tude or DC offset value.

The following restrictions apply when adding DC offset
to the AC waveform:

l

AC amplitude setting wp-p] + 2 +

I DC offset voltage setting [Vp-pl I
llOV with no load
GV with 5OQ load.

l

The amplitude setting must be equal to or larger than
the minimum AC amplitude determined by the sum
of the voltages above. In addition, the DC offset must
not be added to limit the above restrictions. See Table
B-4 (Appendix B) and paragraph 3.5.8 for more details
on these restrictions.

Er FRDTOS

You attempted to set the main synthesizer to output
square waves with variable duty cycle at a frequency
greater than MHz.

Examples:
You attempted to vary the square-wave duty cycle from

50% variable when the frequency is greater than MHz
tith a n waveform.

3-20

You attempted to set the frequency above 1MH.z with the

unit set to output square waves with variable duty cycle.

SECTION3

Operation

l

You attempted to change the sweep time and the
sweep range invalid values during sweep operation.

Er SPLVO9

You attempted to set the main synthesizer oscillation fre­quency above lMJ5I.z with a BESET stop level mode and
an oscillation mode other than CONT.

Examples:
Youatte_mpted tom change the stop level from HOLD to

BESET with the unit set to the TRIG oscillation mode at a
frequency greater than lM.Hz.

You attempted to change the oscillation mode from
CONT to BR!ST with the unit set to the RESET stop level at
a frequency greater than 1MHz.

You attempted to set the oscillation frequency above
1MHz with the unit set to the BESET stop level and the
GATE oscillation mode.

Er MODE10

You attempted to set the main synthesizer oscillation fre­quency above 1OMHz with an oscillation mode other
than the CONT.

Example:
You attempted to set the sweep start frequency and

sweep stop frequency to the same frequency during
sweep operations.

Er RNGE12

Examples:
You entered a value of 9 during waveform selection.
You attempted to set the sweep time to lmsec.

Er CNVT13

The result of the units conversion is outside the allowed
range of the given value.

Example:

Examples:
You attempted to set the oscillation frequency to 12MHz

with the unit set for the GATE oscillation mode.
You attempted to change the oscillation mode from

CONT to BRST with the frequency set to 11MHz.

Er SWPll

l

You attempted to perform sweep operations with an
invalid sweep range and sweep time.

Examples:

You attempted to perform a LOG sweep operation with

the sweep set below 1 octave.

You attempted to begin a sweep operation with the

sweep start frequency and the sweep stop frequency set
to the same frequency.

You attempted to display period units when the fre­quency is set to OHz.

Er MEMO14

An error was found in the backup memory at power
on for one or more parameter settings. If this error oc­curs, preset settings will be placed into effect, and you
should perform front panel calibration after waiting a

few seconds.
An error was found in the contents of the memory
while recalling parameters. Parameter settings will

not be changed, and the Model 3940 will return to the

prompt for the memory number to recall.

Er SYNC15

The slave unit has detected that the power of the master
unit is not turned on during synchronous operation (the

slave unit will not operate properly if the power of the
master unit is off). If the slave unit detects that the power
of the master unit is off, the signal output will be turned

3-21

SECTION 3

Opera f ion

off, and the error display will appear. The Model 3940
slave unit will not recognize further parameter settings
until the power of the master unit is turned on and the er­ror condition is corrected.

Er CAL16

An error has occurred during calibration operations (this
error indicates that the Model 3940 is malfunctioning).
When this error occurs, calibration operations will be ter­minated, and amplitude accuracy will not be guaranteed.

3.5.4 Units Conversion

The Model 3940 can display both frequency and ampli-

tude in different units (frequency can be displayed as pe­riod or frequency, while amplitude can be displayed in
p-p, rms, or dB units). You can convert from one type of
units to another by pressing the appropriate units key
when the Model 3940 is in the appropriate parameter-set­ting mode.

Example:

is truncated for values lower than the resolution) and the
result is displayed. Note, therefore, that the period dis­played as the result of units conversion contains a larger
error when the programmed frequency is high.

Example:

Assume that a main synthesizer frequency of 19.417 475

740 OMHz (actual period of 0.0515pecj is converted to

period display. The value is rounded and displayed as

0.05lysec because of a lnsecresolution limitation. The re­sult is an error equivalent to 0.97% of the correct period.

Amplitude Units Conversion

p-p, rms, or dBm to dBV: Press the dBV key when the

Model 3940 displays the p-p, rms value, or dBm value.

p-p, dBV, or dBm to rms: Press the Vrms or mVrms key

when the Model 3940 displays the p-p, dBV, or dBm
value.

rms, dBV, or dBm to p-p: Press the V or mVrms key when

the Model 3940 displays the rms, dBV, or dBm value.

p-p, rms, or dBV to dBm: Press the dBm key when the

Model 3940 displays the p-p, rms, or dBV value.

Assume that the Model 3940 is in the frequency-setting
mode and displays a current frequency of 1.000 000 OkHz.
Pressing set, ms, or ps converts from frequency to period
units, and the unit displays l.OOOOOmsec.

Note that internal settings remain unchanged when the

uiiits conversion is performed. The

Model

3940 automati=
tally displays the result of units conversion as the current
specified value, and you can modify the value using the
converted units, if desired.

Frequency Units Conversion

Frequency to period: Press the set, ms, or p key when the
Model 3940 is displaying frequency.

Period to frequency: Press the MHz, kHz, or Hz key
when the Model 3940 is displaying period.

The actual, specified value is always displayed for the
frequency, and the frequency accuracy specifications
stated in Appendix B apply. However, the period dis­played is the result obtained by rounding off the recipro­cal of a given frequency to the predetermined number of
digits according to the selected resolution (the reciprocal

3.5.5

Frequency Programming

Pressing the FREQ key displays the current main synthe­sizer frequency and enables main synthesizer frequency
programming. (During a sweep or sweep hold, however,
the frequency cannot be programmed, but the current

c..---.-.- -- ---- -I’11 ?- 1*- ~1

rrequency can snn be alsprayed by pressing FKEQ.j
Pressing SUB FREQ displays the current sub synthesizer
frequency and enables sub synthesizer frequency pro-

gramming.

To program the frequency using the numeric keys, press
the MHz, kHz, or Hz key after entering the value. The
resolution of a frequency value is O.lmHz. When the
specified frequency is below IkHz, the value will be dis­played in kHz units. Above 1kHz and below IMHz, the
frequency will-be displayed in kHz units, and above
IMHz, the frequency will be displayed in MHz units. To
specify the frequency in period units instead of fre­quency units, press one of the time period keys (set, ms,
or pj. Frequency programming for sweep operations is
identical.

The main synthesizer accepts a maximum of six digits
and has a resolution of lnsec. The actual oscillation fre-

3-22

SECTION3

Oweration

quency is obtained by truncating the reciprocal of the
given value to an acceptable number of digits on the part
of the value smaller than O.lmHz.

The sub synthesizer accepts a maximum of six digits with

a resolution of loons. The actual oscillation frequency is
obtained by truncating the reciprocal of the given value
to an acceptable number of digits on the part of the value
smaller than O.lmHz.

When frequency programming is enabled, you can
change the present value with the MODIFY knob. The
knob can be used to change the value during both fre­quency display and period display. When the step size is
fl, you can select the digit to change by placing flashing
underline cursor under the appropriate digit and turning
the MODIFY knob to the right or left. When the step size
is x+2 or x+10, the cursor will disappear, and you can di­vide or multiple the value by 2 or by 10 by turning the
knob to the left or right.

Note that when the displayed period is obtained from a
frequency specified with an insufficient number of digits,

the actual oscillation frequency may not be changed even
if the value is changed with a numeric key or the MOD­IFY knob. The Mode13940 always displays a correct value
for frequency.

when setting the frequency, you can use MODIFY to

change the amplitude.

The AMl?TD key sets the amplitude for AC waveforms

only; use the OFFSET key to set the DC output voltage of
the DC waveform type. When the DC waveform is se­lected, you still can program the amplitude, but that
value can be entered only in p-p units (the allowed ampli­tude ranges from 2.OOmV p-p/no load to 2O.OV p-p/no
load). The specified value is stored, and it is used as the
given amplitude for the next selected AC waveform.

For AC waveforms with OV DC offset, you can specify
any value within the maximum and minimum allowed
amplitude limits without restrictions. If, however, the
programmed DC offset is not OV, certain restrictions con­cerning the maximum allowable amplitude apply. Para­graph 3.5.8 describes these restrictions in more detail.

When the main synthesizer amplitude is changed, an off­set voltage may appear at the output jack for less than
lmsec until the output stabilizes at its new value. In addi­tion, an amplitude setting change that causes output at­tenuator switching may cause the output to be turned off
for about 100msec during switching.

3.5.7

DC Offset Programming

3.5.6 Amplitude Programming

Pressing AMPTD displays the current main synthesizer

amplitude and enables main synthesizer amplitude pro­gramming. Similarly, pressing SUB
present sub synthesizer amplitude and allows sub syn-

thesizer amplitude programming.

When using numeric keys to set the amplitude, press the
appropriate units key to complete the entry process.
Press V or mV to enter p-p units, use Vrms or mVrms for
rms units, or press dBV or dBm for dB units. Note that
dBm units do not apply to the sub synthesizer amplitude,
and that only dBV and dBm units can have negative val-

UeS.

The rms and dBV values are set on the assumption that
the average or center level of the peak-to-peak amplitude
of the waveform is OV. Thus, these values do not depend
on the DC offset value or square-wave duty cycle. As

AMPTD displays the

Pressing the OFFSET key displays the current DC offset
value and enables main synthesizer offset programming.
Note that the DC offset is programmable only for the
main synthesizer; the sub synthesizer has no program­mable offset.

When using the numeric keys to set the offset, press the V
or mV key after entering the value to complete the entry
process. As with other parameters, you can also use
MODIFY to change an existing offset value.

With a DC waveform, the programmed offset voltage is
the DC voltage value that appears at the output jack.
Valid offset values are within the range of +lOV to -lOV.

For all AC waveforms, the DC offset is added to the aver­age value of the peak-to-peak amplitude of the AC

waveform. Certain restrictions apply for amplitude-off-

set combinations, and some combinations of values may
cause an error (Er ACDC07) to occur. See paragraph 3.5.8
below for more details.

3-23

SECTION 3

Operation

When a DC offset setting that causes a change in output
attenuators is programmed, the output may be turned off
for approximately 1OOmsec during the switching period.

3.5.8 AC Amplitude and DC Offset
Relational Restrictions

AC amplitude and DC offset settings are subject to rela­tional restrictions. See Table B-4 (Appendix B) and
Figure 3-8 for more details on the interaction between
these two parameters.

These restrictions are a result of the limitations in the
maximum output voltage of the output amplifier. When
the DC offset is added to the AC waveform, the output
voltage peak will be the sum of the DC offset voltage and
half of the AC waveform amplitude. This voltage is
known as the total set voltage and is related as follows:

Set AC amplitude

Total Voltage =

Example:
An error will occur when you try to set the DC offset to

GV/open when the amplitude is 1OV p-p/open. (The to­tal voltage exceeds lOV/open.)

(VP-P)

2

+ I Set DC offset voltage 0 I

Example:
An error will occur when you try to set the amplitude to

1OOmV p-p/open when the DC offset is 5V/open. (The
minimum AC amplitude when the total voltage is over
lV/open is 200mV p-p. The amplitude setting is below
the minimum amplitude value.)

Even valid combinations may cause errors in the process
of setting up those combinations. To avoid such errors,
reset the DC offset value to OV before changing the ampli­tude, or change the setting specified in Figure 3-8 so that
the values are within the range of allowed settings.

Example:
Suppose that the current amplitude is 1OOmV p-p/open

and the DC offset is 500mV/open. Assume that you want
to use an amplitude of 500mV p-p/open and a DC offset
of 5V in combination. An error will occur if you set the
DC offset to 5V before setting the amplitude. (The mini­mum AC amplitude when the total voltage is over lV/

open is 200mV p-p. The amplitude setting is below the
minimum amplitude value.) If you set the amplitude to
500mV p-p first, and then set the DC offset to 5V, you can
obtain the desired amplitude and offset values without

causing an error.

3-24

100m

SECTION 3

Operation

bm

=a

loltage

ov

DC Offset

Voltage

t/-V/open circuit)

10m

lm

Figure 3-8.

im 10m

Relational Range for Allowed AC Amplifude Voltage and DC Offset Volfage

loom

AC Amplitude Voltage (VP-p/open)

1

IO

100

SECTION 3

Operation

3.5.9 Waveform Selection, Square-Wave
Duty Factor, and Synchronous
output

Waveform Selection

Pressing the FCTN key displays the current main synthe­sizer waveform along with its corresponding number
and enables main synthesizer waveform selection. Avail-

able main synthesizer waveforms include: DC, SIN <2/ >,

2/,n,n,&ndARB.

Pressing SUB FCTN displays the current sub synthesizer
waveform along with its with its corresponding number
and enables sub synthesizer waveform selection. Sub

synthesizer waveforms include: SIN &>, 2/, n , A,
and\.

To select a waveform with the numeric keys, simply
press the numeric key that corresponds to the desired
waveform. For example, press 1 to select a sine wave. The
waveform will change immediately when the corre-

sponding key is pressed; it is not necessary to press a

units key.

When the Model 3940 displays the current waveform,

and function parameter selection is enabled, you can
change the waveform by turning the MODIFY knob.
Turning the knob clockwise increases waveform num­bers, while turning the knob counter-clockwise decreases
waveform numbers (one number increment per knob
detent). When the highest or lowest waveform numbers
are reached, the number will wrap around to the lowest
or highest selection (main synthesizer numbers range
from 0 through 6, and sub synthesizer numbers are from
1

to

5).

For all AC waveforms, the p-p value of the amplitude

will remain unchanged when you change the waveform.

If the amplitude is specified in units other than a p-p
value, the amplitude will be converted to p-p units when
the waveform is changed.

Square-Wave Duty Cycle

The duty cycle is the ratio of the time period of the
waveform high-level duration to the time period of one

complete cycle of the waveform expressed as a percent­age. For example, a 1OkHz square wave has a time period
of 1OOlLsec. If the high portion of the waveform has a pe­riod of 30pec, the duty cycle is 30/100 x 100 = 30%.

Two square-waveform duty-cycle modes are available:
one with the duty cycle fixed at 50% and the second mode
with a variable duty cycle. The duty cycle applies only to
the square-wave function (waveform 3), although the
duty cycle can be programmed while other waveforms
are selected.

To change the duty cycle, press the k DUTY key, and en­ter or modify the duty cycle (5.0% to 95.0%). The Model
3940 stays in the variable duty cycle mode even if you set
the duty cycle to 50%. To select the fixed 50% duty cycle
mode, press SHIFT FXD50. In the duty cycle display
mode, the Model 3940 displays “FXD” for the 50% fixed
mode or “VAR” for the variable duty-cycle mode.

When the Model 3940 is in the variable duty-cycle mode,
the upper-frequency limit is lMHz, and the maximum jit­ter is 15nsec or less. The Model 3940 has a resolution of

0.1% for duty-cycle display, but the hardware resolution
is 0.4% (8 bits). As a result, if you make a duty-cycle
change lower than the hardware resolution cycle, only

the displayed value will change, not the duty cycle of the

actual output.

To extend the duty cycle range, use the burst oscillation
mode and one square waveform cycle.

Example:
Set the mark number of cycles to 1 cycle, the space num-

ber of cycles to 9 cycles, the phase to -9O”, and the stop
level to HOLD with the unit in the burst oscillation mode.
With these settings, the square-wave duty cycle will be
10%.

Synchronous Output

Figure 3-9 illustrates the phase relationship between the
waveform and synchronous outputs at frequencies be­low 1kHz. Typical jitter between the main synthesizer
waveform output and the main synthesizer synchronous
output is about 9.lnsec. Typical jitter between the sub
synthesizer waveform output and the sub synthesizer
synchronous output is approximately 291nsec.

3-26

SECTION3

Orxration

SYIIC

output

Main synthesizer square wave with
variable duty cycle

I

r-u

I

Sub synthesizer ascending

Main synthesizer square wave

1

with duty cycle fixed at 50% or
1 sub synthesizer square wave
I

I

Main synthesizer ascending

I

sawtooth wave

Descending sawtooth wave

I

*

I

I

Figure 3-9.

I

Sync
output

Ll-l

Phase Relationship Between Waveform and Synchronous Oufpuf

Sync
output

rLl

3-27

SECTION 3

3.5.10

Oscillation Mode and Trigger
Source Selection

Oscillation Mode Selection

Pressing the MODE key displays the current main syn­thesizer oscillation mode along with its corresponding
number and enables main synthesizer oscillation mode
selection. Available oscillation modes include continu­ous, burst, trigger, and gate modes. These oscillation
modes are applicable only to the main synthesizer and do
not apply to the sub synthesizer.

To select the oscillation mode with the numeric keys,

simply press the numeric key that corresponds to the de­sired oscillation mode. For example press 1 to select the
burst mode. Pressing the numeric key will change the set­ting immediately; it is not necessary to press a units key
when setting the oscillation mode.

When the Model 3940 displays the current oscillation
mode and mode selection is enabled, you can also change

the mode by turning the MODIFY knob. Turning the
knob clockwise increases the oscillation mode number,
while turning the knob counter-clockwise decreases the
oscillation mode number (one digit per detent setting).
When the highest or lowest mode number is reached, the
number will wrap around to the lowest or highest value

(mode values range between 0 and 3). Note that the cur­sor position is fixed, and the step size is fixed at +l.

Continuous Mode

and space values will have no effect on the output
waveform.

Burst Mode

In the burst mode, the instrument will generate the se­lected waveform for the number of mark cycles and then
stop oscillations for the number of space cycles. This on­off cycle of oscillations will be generated repeatedly.

For example, if the number of mark cycles is set to 1.5 cy­cles and the number of space cycles is set to 4.0 cycles, the
unit will oscillate for 1.5 cycles and will stop oscillations
for 4 cycles repeatedly. Figure 3-10 demonstrates the on­off characteristics of the burst oscillation mode.

Trigger Mode

In the trigger mode, the unit will generate the number of
cycles of oscillation determined by the mark parameter
each time the trigger signal is received. The Model 3940

will ignore other trigger signals while generating the

specified number of waveform cycles. In other words, a
trigger functions only when the Model 3940 is not gener­ating oscillations.

For example, if the mark parameter is set to 2.0 cycles, and
a trigger signal is received, the Model 3940 will oscillate
for 2 cycles. Any trigger signal received will be ignored
during this period. When the 2-cycle oscillation period is
completed, the Model 3940 will begin the oscillation stop
phase, and triggers will then be enabled.

When the continuous mode is selected, the instrument
will generate the selected waveform continuously. Trig­gering or gating is not required, and the selected mark

Mark wave Space wave

cycle: cycle:

1.5 cycles 4 cycles
Oscillation

stop

Mark wave Space wave
cycle cycle

Oscillation stop

F&we 3-10. BURST Oscillation

3-28

Figure 3-11 demonstrates the trigger oscillation mode.
Note that the source of the trigger is proDammed with
the SOURCE key.

Mark wave
cycle

Oscillation

SECTION 3

Oneration

Mark

wave cycle:

2-cycle oscillation

when trigger is received

Stop until the

I

Trigger signal

(When trigger source is

Figure 3-11.

Gate Mode

next trigger

_f )

Trigger Oscillation

The next trigger will be
Ignored during oscillation

\

In the gate mode, the unit will generate oscillations as
long as the gate signal (trigger signal) is on. When the
gate signal turns off, the Model 3940 will always stop os­cillating at half-period point of the cycle even if the gate
signal turns off before the half-period point of the cycle is
reached. These gate mode characteristics are shown in
Figure 3-12.

Trigger Source Selection

Pressing TRIG SOURCE displays the current trigger
source with its corresponding number and enables trig­ger source selection. Available trigger sources include ex­ternal (a trigger signal applied to the EXT TRIG IN jack),
and internal (sub synthesizer sync signal). Rising-edge

(5) and falling-edge ( ?L ) signals can be selected for
both external and internal trigger sources. Note that se­lecting internal trigger automatically selects the sub syn-

thesizer synchronous output signal as a trigger source.

In the trigger oscillation mode, the trigger will be gener­ated on the rising edge of the input signal if 4
or on the falling edge of the input signal if%

is selected

is selected.
Similarly, in the gate oscillation mode, the gate signal is
considered to be on at a high logic level in the 5 mode,
and the gate signal is considered to be on at a low logic
level in the x mode.

In the gate oscillation mode with the trigger source set to
external&, the gate signal will be on, and the Model 3940
will oscillate continuously when the EXT TRIG IN BNC
connector is left disconnected. This situation is the result
of the internal pull-up resistor connected to the external
trigger input. Thus, leaving the external trigger input
connector disconnected is equivalent to connecting a
high logic level.

For example, oscillation starts when the gate signal (trig­ger signal) turns on with the unit in the oscillation stop
mode. If the gate signal goes off after 4.1 cycles, oscilla­tion will not stop immediately at this point but will con­tinue until 4.5 cycles have been generated. Once this
point is reached, the unit will enter the oscillation stop
mode, and oscillations can be restarted by the gate signal.

Gate

i

ON
OFF

start when the
gate signal is on

\

Half-period cycle oscillation
will be completed and will stop
when the gate signal is off

yzle oscillation
lleted and will stop

te signal is off

1 Fiatre 3-12. Gate Oscillation

3.511

Mark, Space, and Phase Parameter
Programming

Mark and Space Parameter Programming

Pressing the MARK key displays the current mark pa­rameter and enables mark parameter programming.
Similarly, pressing the SPACE key displays the present

space parameter and enables space parameter program­ming.

To program the mark and space parameters using the nu­meric keys, key in the desired value, and press any one of
the ENTER keys to complete the entry process.

The allowed range for the mark and space parameters is

I

from 0.5 cycle to 32768.0 cycles with 0.5 cycle resolution.

The fractional part of input values will be rounded to .O or

.5.

3-29

SECTION 3

Oueration

When the Model 3940 displays the current mark or space
value, and parameter entry is enabled, you can change

the mark or space value with the MODIFY knob.

When the step size is fl, you can specify the digit to mod­ify by placing the flashing cursor under the appropriate
digit and turning the MODIFY knob to the right or left.
When the step size is x12 or x+10, you can divide or mul­tiply the value by the step size by turning the MODIFY
knob to the left or right.

The mark parameter applies to both the burst mode and
trigger modes, and the same value is used by both. How­ever, the space parameter applies only to the burst mode.
Either parameter can be programmed while the instru­ment is in any oscillation mode, but they will be in effect
only for the applicable modes (burst or trigger).

Phase

Pressing PHASE displays the current main synthesizer
phase and allows setting of that parameter. Similarly,
pressing SUB PHASE displays the present sub synthe­sizer phase and enables sub synthesizer phase program­ming.The allowed range for both main and sub synthe­sizer phase parameters is from -360.0“ to 360.0” with 0.1”
resolution.

The Model 3940 generates the main synthesizer sine
wave synchronous output, as well as square waves with
fixed 50% duty factor and their synchronous output by
processing sine waves with a zero-crossing comparator
that has hysteresis. The level of the generated square
wave, therefore, alternates high and low at approxi­mately 0”, rt180”, and rt360” depending on the history

(past value) of the phase.

Note that the unit may generate distorted waveforms
caused by overshoots for oscillation modes other than
CONT during the transition to the stop phase. To set the
start/stop level high, set the start/stop phase to a high
value; to set the start/stop level low, set the start/stop
phase to a low value. ,

Other main synthesizer waveform synchronous outputs
and square waves of variable duty factor are generated
digitally. Maximum jitter for these waveforms is 15nsec

(9.lnsec typical).

Main synthesizer phase settings apply to the start phase
of the burst oscillation, trigger oscillation, and gate OS&
lation modes of the main synthesizer. When oscillation
begins from the oscillation stop mode, oscillation will re­sume from the phase specified with this phase setting.

Phase definitions for the available waveforms are illus­trated in Figure 3-13.

This phase setting can also be used as an oscillation re­sume phase when phase sync is used. See paragraph

3.5.12 for more details.

330

Main synthesizer square wave with duty

cycle fixed at 50% above 100 kHz.
CONT mode or stop level:

RESET using modes other than CONT.

Center of
peak-to-peak
amplitude

i i

Square waves other than

1

those listed at left

SECTION 3

Operation

About +I- 1.2” About +/- 1.2’

w i /+-

I I

O0 O0

The shaded portion is the hysteresis area
in which the level goes high and low
depending on the past value of the phase

Main synthesizer square wave of
variable duty cycle

0”

I

180" 180" 360° 360°

360"

i

I

Phase

I

Descending sawtooth wave

I

i
I

i

I

i

00

I

i

180" 360" -

I

I

! -

Fijq4re 3-13.

Waveforms

and Phase Definitions

3-31

SECTION 3

3.5.12 Stop Level and $ SYNC

Stop Level Selection

Pressing SHIFT STOP LEVEL enables stop level pro­gramming. The stop level applies to the burst oscillation,
trigger oscillation, and gate oscillation modes, and it de­termines the output level during the oscillation stop
mode.

The Model 3940 has two stop level modes: HOLD (0) and
RESET (1). With the HOLD mode, the oscillation stop
level is set to the same value as the output level at the os­cillation start phase. With the RESET mode, the output is
set to the center value of the waveform during the oscilla­tion stop mode.

Example:
Figure 3-14 shows an example using the HOLD stop level

mode with a 30” phase setting and a sine wave. The out­put during the stop mode is at the same level as the 30’
phase point (at half the waveform peak level for a sine
wave).

I

90” 90” 90” 270”

1 cycle

oscillation

stop
level

1.5&le

oscilliation

I Figue 3-15. Waveform Examples with Reset Stop Level

$I SYNC

Pressing SHIFT Cp SYNC enters the phase sync mode and
generates the phase sync pulse. The purpose of the phase
sync pulse is to restart the waveform from the set phase
value.

Phase sync operation is guaranteed only for the continu­ous oscillation mode of the main synthesizer. Phase sync
can be used to synchronize master and slave synthesizer
phases when using two Model 3940s synchronously, and
it can also be used to internally synchronize main synthe­sizer and sub synthesizer phases.

30”

Figure 3-14.

Waveform Examples with Hold Stop Level

300 30” 210” -30” Level

1 cycle stop 1.5 cycle

oscillation level oscilliation

--

Example:
Figure 3-15 shows an example of the RESET stop level

mode. Conditions for this waveform are: Stop level: RE­SET; waveform: sine wave; phase: 90”; amplitude: 2V
p-p; offset v It o age: OV. The output level during the
waveform stop mode will be at center value of rtlV (2V
p-p) value, or OV. Since the oscillation start phase is 90”,

the output level will rapidly change from OV to 1V (the
voltage at the 90” point) at the start of the oscillation
phase. Since the oscillation phase ends at 90” or 270”, at
which point the oscillation stop mode begins, the output
will rapidly change from 1V or -1V to the OV stop level,

and will maintain that OV value until the next oscillation
phase begins.

Example:

I

Figure 3-16 demonstrates phase sync operation between
the main and sub synthesizers. The main synthesizer fre­quency is 1kHz and its phase is 0’; the sub synthesizer
phase setting is 90”. If the sub synthesizer frequency is
lkHz, which is identical to the main synthesizer fre­quency setting, two identical waveforms with different
phase characteristics can be observed with an oscillo­scope. The constant phase relationship between the two
waveforms is the result of the identical 1kHz frequencies
of the two signals, and, although the phase settings may
differ by exactly 90”, the actual phase difference between
the two signals may not necessarily be exactly 90”.

If the $ SYNC key is pressed at this point, both

waveforms will restart at their initial phase settings (O”

for the main synthesizer signal, and 90” for the sub syn­thesizer signal). Thus, the phase of the sub synthesizer
output will be approximately 90” relative to the phase of

the main synthesizer output, and accurate phase rela-

tionships between the two signals will be maintained re­gardless of the individual phase settings.

The time between the phase sync pulse and the restart of

the waveform differs between the main synthesizer and

sub synthesizer. In addition, this delay time will vary de-

3-32

SECTION 3

Operation

pending on the waveform type. As a result, deviations in
the phase relationships may be greater at higher frequen-

cies when using phase sync. You can manually fine tune
the phase settings of the two synthesizers to obtain a
more accurate phase relationship. See the specifications
in Appendix B (synchronous operation) for more details
on delay time.

When phase relationships are more accurately defined
through phase sync, the Model 3940 can be used as a two­phase oscillator with accurate phase relationships be­tween the main and sub synthesizer signals. The phase of
either synthesizer signal can be changed, and an accurate
phase relationship between the two will be maintained
once phase sync has been initiated.

Example:
If the main synthesizer and sub synthesizer signals are

90” out of phase (as in the previous example), and both
phase settings are changed to 0”, the phases of the two
signals will be identical (O’), and the two signals will be
exactly in phase. If both phases are set to 90”, the phases
will again be identical (90% and the two signals will also
be exactly in phase. If the phase of either signal is set to

180”, the two signals will be out of phase.

Example:
Figure 3-17 demonstrates phase sync operation with sig-

nals at two different frequencies. Here, a phase sync op-

eration is performed with main synthesizer frequency at
2kHz and the sub synthesizer at IkHLz. Under these con­ditions, the main synthesizer O” point will correspond to

the sub synthesizer 0” phase point.
If the main synthesizer phase is subsequently set to 45”,

the main synthesizer 45” point will now correspond to

the sub synthesizer 0” phase point. If the main synthe­sizer phase is set to 0” and the sub synthesizer phase is set

to 45”, the main synthesizer 0” point will correspond to

the sub synthesizer 45” point.

a SYNC

atlkHz

Figure 3-16. Phase Sync Operation

Both O” points
will correspond

Main synthesizer 45” point and Main synthesizer 0” point and
sub synthesizer 0’ point sub synthesizer 45” point
will correspond will correspond

Figure 3-l 7. Phase Relationship aj%er Phase Sync

3-33

SECTION 3

Operation

3.513 Synchronous Operation

Multiple Model 3940s can be connected together syn­chronously to form a multiphase oscillator. The phase re­lationship between the oscillators can be accurately de­fined by using @ SYNC.

With the units turned off, connect the optional Model
3949 Synchronous Cable to the PHASE SYNC I/O con­nector on the rear panel of each unit. The Model 3940
with the connector labelled “MASTER” is the master unit
and transmits clock and phase sync pulses to the slave
unit. The Model 3940 with the connector labelled

“SLAVE” is the slave unit that receives clock and phase
sync pulses transmitted from the master unit. Note that
slave unit I$ SYNC key will be inoperative, and the slave
unit will not respond to the GPIB “SYN” command.

After connecting the units and setting up waveforms and
frequencies, press the $ SYNC key on the master unit to
synchronize phases. You can then set the phases for the
units independently, and accurate phase relationships
between waveforms from the two instruments will be
maintained. The $ SYNC phase relationships for external
synchronous operation are similar to those discussed
previously for main synthesizer and the sub synthesizer
phases (see paragraph 3.5.12).

3.514

Frequency Sweep Operation

If you specify the center and span frequencies to set the

sweep range, the Model 3940 will automatically convert

them into start and stop frequencies. See the specifica­tions in Appendix B for more details on the sweep range
and sweep width.

The Model 3940 determines the sweep range as described
below when you change a frequency parameter:

When you change the start frequency:
The stop frequency remains unchanged.

Center frequency =
(start frequency + stop frequency)/2
(Portion of value below O.lmHz is truncated.)
Span frequency = I start frequency-stop frequency I

When you change the stop frequency:
The start frequency remains unchanged.

Center frequency =
(start frequency f stop frequency)/2
(Portion of value below O.lmHz is truncated.)

Span frequency = I start frequency - stop frequency I
When you change the center frequency:

The span frequency remains unchanged.
The relationship between the start and stop frequency
values remains the same as it was before you changed
the center frequency:
Start frequency =

(center frequency T span frequency/2)

(Portion of value below O.lmHz is truncated.)
Stop frequency =
(center frequency + span frequency/2)
Portion of value below O.lmHz is truncated.)

The Model 3940 can be set up to generate frequency
sweeps over a variety of ranges. The following para­graphs discuss the various aspects of programming fre­quency sweeps. Figure 3-18 shows sweep waveforms,
and Figure 3-19 details sweep operation.

Setting the Sweep Range

You can set the sweep range in one of two ways: (1) by
setting the start and stop frequencies, or (2) by setting the
center and span frequencies. The actual sweep is gener­ated from the start frequency to the stop frequency, and
the sweep direction is determined by the relative values
of the start and stop frequencies. If the start frequency is
lower than the stop frequency, an ascending-frequency
sweep will be generated. If the start frequency is higher
than the stop frequency, a descending-frequency sweep

will be generated.

3-34

When you change the span frequency:
The center frequency remains unchanged.

The relationship between the start and stop frequency

values remains the same as it was before you changed
the span frequency:
Start frequency =

(center frequency T span frequency/2)
(Part smaller than O.lmHz is truncated.)

Stop frequency =
(center frequency & span frequency/2)

(Part smaller than O.lmHz is truncated.)

The start and stop frequencies always correspond to the
opposite ends of the actual sweep range. When the span
frequency is an odd number of O.lmHz units, the dis­played center frequency will be 0.05mHz lower than the
actual center frequency value. The center frequency is the
center frequency on the linear scale, and it is not the cen-

SECTION 3

Oneration

ter frequency based on the sweep time in the log sweep
mode.

Sweep

Time

Sweep time will vary depending on the selected sweep
function.

l

When the sweep function is A:

Sweep time L

time of transition from start fre­quency to stop frequency

=

time of transition from stop fre­quency to start frequency

=

half of repetition period of contin­uous sweep

* When the sweep function is A:

Syeep time

= time of transition from start fre-

quency to stop frequency

= repetition period of contin-

uous sweep

l

When the sweep -fur&or&~ :

Sweep time = duration of start frequency in con-

tinuous sweep

= duration of stop frequency in con-

tinuous sweep

= half of repetition on continuous

sweep

When the sweep times for the A and/l sweep functions
are identical, the sweep rate along the equivalent sloped
portions of the two waveforms will also be identical.
Note, however, that the continuous-sweep repetition pe­riod for the two functions is different. See Figure 3-18 for
more details on sweep progression.

Starting a continuous sweep (CONT START key).
Starting a single sweep (SINGL START key).
Holding and resuming a sweep (HOLD/RESM key).
Turning a sweep off to enable normal frequency pro­gramming (SWEEP OFF key).
Setting the output waveform to the start frequency

(START STATE key).

Setting the output waveform to the stop frequency

(STOP STATE key).
Starting a single sweep with external signals (SINGL
START IN BNC jack).
Holding and resuming a sweep with external signals.

(HOLD IN BNC jack).

Starting a Continuous Sweep

To start a continuous sweep, press SHIET CONT START.
During the sweep, the Model 3940 displays the sweep
frequency, and the following message is displayed:

“CONT SWEEP EXEC (EXIT:SWEEP OFF)“. When the
Model 3940 is in this mode, you cannot set the frequency
with the FREQ key.

Starting a Singie Sweep

Press the SINGL START key to initiate a single sweep.
During a single sweep, the Model 3940 displays the
sweep frequency, and the following message is dis­played: “SJNGL SWEEP EXEC (EXITSWEEP OFF)“. You
cannot set the frequency with the FREQ key while the
unit is generating a single sweep.

When the Model 3940 terminates a single sweep, it dis­plays the terminated sweep frequency along with the fol­lowing message “SINGL SWEEP END”. Once the sweep
has terminated, you can program the output frequency
with the FREQ key.

Sweep Operations

Model 3940 sweep operations include the following eight
types of sweeps:

The MKR OUT and SWEEP SYNC OUT signals go high,
and the X DRIVE OUT signal is set to OV at the end of the
sweep.

3-35

SECTION 3

Operation

Figure 3-18. Sweep Frequency and Sweep Output

3-36

SECTION 3

Operation

HOLD IN:
LOW LEVEL

SINGL START IN:
FALLTIME

SINGLE SWEEP

HOLD MODE

SINGLE SWEEP

OPERATION MODE OPERATION MODE

CONTINUOUS SWEEP

HOLD MODE

CONTINUOUS SWEEP

Figure 3-19.

START FREQUENCY

OUTPUT MODE

Sweep Operation

NORMAL MODE

STOP FREQUENCY

OUTPUT MODE

SECTION 3

Opera f ion

HoIding/Resuming a Sweep from the Front Panel

To temporarily halt execution of a continuous or single

sweep, press the HOLD/RESM key. The Model 3940
stops the sweep operation immediately, and it displays
the frequency at which it stopped the sweep. The MKR
OUT, SWEEP SYNC OUT, and X DRIVB OUT signals
maintain their current values when the sweep is halted.

When a continuous sweep is paused, the Model 3940 dis-

plays “CONT. SWEEP HOLD (EXITSWEEP OFF)“; simi­larly the unit displays “SINGL SWEEP HOLD
(EXITSWEEP OFF)” when a single sweep is paused.
When the Model 3940 is in the sweep hold mode, you
cannot program the frequency with the PREQ key.

To resume a sweep starting at the frequency at which you

stopped sweep operation, press the HOLD/RESM key
again.

Turning a Sweep Off to Enable Normal Frequency Pro­gramming.

Press the SWEEP OFF key during a sweep or sweep hold
to turn off a sweep and enable normal PREQ key pro­gramming. The MKR OUT and SWEEP SYNC OUT sig­nals will be set high, and the X DRIVE OUT signal will be
set to OV.

When the SWEEP OFF or FRBQ keys are pressed at the
completion of a single sweep, during start frequency out­put, or during stop frequency output, normal frequency
programming will be enabled. In addition, the MKR
OUT and SWEEP SYNC OUT signals will be set high, and
the X DRIVE OUT signal will be set to OV.

Setting the Output to the Start Frequency

Press the START STATE key to set the output waveform
to the programmed start frequency. During this mode,
the Model 3940 displays the start frequency along with
the following message:

“SWEEP START STATE”. The

MKR OUT and SWEEP SYNC OUT signals also go high

during the start frequency mode. The X DRIVE OUT sig­nal is set to OV if the start frequency is lower than the stop

frequency; it is set to 1OV if the start frequency is higher

than the stop frequency.

When the Model 3940 is in this mode, pressing the PREQ
key enables normal frequency programming with the
FREQ key and sets the X DRIVE OUT signal to OV.

Setting the Output to the Stop Frequency

Press SHIFT STOP STATE to set the output waveform to
the programmed stop frequency. While in this mode, the
Model 3940 displays the stop frequency along with the
following message: “SWEEP STOP STATE”. During the
sweep stop state, the MKR OUT and SWEEP SYNC OUT
signals are set high. X DRIVB OUT is set to 1OV if the start
frequency is lower than the stop frequency; it is set to OV
if the start frequency is higher than the stop frequency.

When the Model 3940 is in this mode, pressing the FRBQ
key enables normal frequency programming with the
FREQ key and sets the X DRIVE OUT signal ,to OV.

Starting a Single Sweep Using an External Signal

A TTL-level, falling-edge signal, applied to the SINGL
START IN BNC connector, starts a single sweep. This sig­nal performs essentially the same operation as pressing

the SINGL START key.

SINGL START IN is internally pulled up to a high logic
level, and sweep operation is not affected when the this

connector is left disconnected from external signals.

Holding/Resuming a Sweep with an External Signal

A TTL low-level signal, applied to the SWEEP HOLD IN
BNC connector, places the Model 3940 in the sweep hold
mode. In the sweep execution mode, the Model 3940 halts
the sweep as long as this input remains low. If you at­tempt to start a sweep when this input is low, the Model
3940 immediately enters the sweep hold mode. Note that
pressing HOLD/RBSM does not resume sweep opera­tion with the hold signal held low; you must set SWEEP
HOLD IN high to resume the sweep.

SWEEP HOLD IN is internally pulled up to a high logic
level, and sweep operation is not affected when this con­nector is leftdisconnected from external signals.

338

SECTION 3

Operation

Sweep Frequency and Sweep Output

Figure 3-18 illustrates how the sweep frequency and the
MKR OUT, SWEEP SYNC OUT, and X DRIVE OTJT sig­nals change with time.

The MKR OUT signal is high when the sweep frequency
is higher than the marker frequency. When the sweep

function is A or 1, the high signal level is maintained
even after a single sweep is terminated.

The SWEEP SYNC OUT signal goes low during the tran­sition from the start frequency to the stop- frequency.
When the sweep function is 1, the frequency changes at

the center point of this output signal.

The X DRIVE OUT jack supplies a voltage that varies be­tween OV and 1OV in proportion to the lapse of sweep

time, and according to the direction of the sweep fre­quency. The X DRIVE OUT signal also varies linearly
with time in the log sweep or step sweep mode.

Example:
To change a 5kHz center frequency and an 8kHz span fre-

quency to 2kHz and 3kHz respectively, you must first
change the span frequency to 3kHz and then change the
center frequency to 2kHz. If you first change the center
frequency to 2kHz, an error will occur because this com-

bination would result in a start frequency of -2kH.z.

Number of Steps in a Sweep

Sweep operation of the Model 3940 is timed by fixed-in­terval interrupts, which results in accurate sweep timing
with specific, accurately timed sweep steps. As a result,
the actual sweep time will never exceed the actual pro­grammed sweep time. In addition, the number of sweep
steps will simply increase or decrease as sweep time is
changed.

The number of steps in sweep can be calculated as out­lined below.

Linear Sweep Steps

Substituting Marker Frequency for Center Frequency

Press SHIFT CTRI to set the center frequency to the cur­rent marker frequency value. This operation produces

the same result as programming an identical frequency
with the numeric keys. The marker frequency is not af­fected by this operation.

Changing Settings During Sweep Operation

Because of processing execution time in the sweep execu-

tion mode, the Model 3940 may respond to the keys and
Gl?IB commands more slowly than in other modes. If you
change the sweep range, sweep time, or sweep function
with MODIFY while the Model 3940 is in the sweep exe­cution mode, the unit will recalculate the new parameters
each time you change the setting, resulting in slower re­sponse.

If you set the sweep range based on center and span fre­quencies, an error may occur depending on the order of
parameter selection whether or not the Model 3940 is in
the sweep execution mode.

Within a linear sweep, output frequency is changed
every 250pec. Therefore, the number of steps can be cal­culated as follows:

Number of steps: Sweep time (set) x 4000

The number of steps represents the number of frequency
changes that occur between the start frequency and the

stop frequency. With the A sweep function, the number
of steps also represents the number of frequency changes
between the stop frequency and the start frequency.

If the single-step frequency increase/decrease width is
equated to the step width, the step width can be repre­sented as follows:

Step Width (Hz) =

Sweep width (Hz)

Number

of steps -1

The frequency resolution of the step width may not be a

whole number of O.lmHz units. As a result, the fre­quency-variable width of a single step is:

Step width: ti.lmHz.

3-39

SECTION 3

Operation

The MKR OUT signal is synchronous with the sweep
steps. With an ascending sweep, the MKR OTJT signal is
low when the sweep frequency is higher than the marker
frequency. With a descending sweep, the marker output
is high when the sweep frequency is lower than the
marker frequency. The deviation between the set marker
frequency value and the actual transition in the MKR
OTJT signal is:

Marker Deviation (Maximum): Z!I Step width (Hz)

The X DRIVE OUT signal will also change synchronously
as the sweep progress. Resolution of this output signal is
10 bits.

Log

Sweep Steps

With log sweeps, the output frequency is changed every
500psec. Frequency update is slower in log sweep than in

linear sweep due to the calculations required for log
sweeps. Consequently, the number of steps for log
sweeps can be calculated as follows:

Number of steps: Sweep time (set) x 2000

If the single-step frequency increase/decrease multiplier
is equated to the step multiplier, the step multiplier can
be calculated as follows:

log-’ (log 10

Stop frequency (Hz)

Start frequency (Hz)

+ (Number of steps -1))

The step width (frequency) will change as the sweep pro­gresses. The deviation between the set marker frequency
and the MKR OUT signal is:

Marker Deviation (Maximum.): -t-Step width (Hz)

3-40

SECTION 4

GPIB OPERATION

4.1 INTRODUCTION

4.1 .l

The GPIB Interface is a general-purpose interface bus
system recognized by the IEEE (Institute of Electrical and
Electronics Engineers) in 1975 and is a method of Stan­dardizing data transfer between measuring instruments
and peripherals. By building each controller and periph­eral device into an interface conforming to this standard,
it is possible to establish complete hardware compatibil­ity among devices.

Up to 15 devices may be connected to a single interface
bus and data transfer is performed by three handshake
lines, enabling reliable data transfer between data send-

ers (talkers) and receivers (listeners) having differing
data transfer rates.

GPIB Overview

4.12 Major GPIB Specifications

Overall cable length: 20m maximum
Cable lengths between devices: 4m maximum
Number of devices connectable

(including a controller): 15 maximum
Transfer method: 3-Line handshake
Transfer rate: 1M bytes/set (maximum)
Data transfer: 8-bit parallel
Signal lines:

Data bus: 8 Lines
Control bus: 8 Lines
(including DAV, NRFD, and NDAC handshake
lines and ATN, REN, IFC, SRQ, and EOI

control lines)
Signal/system grounds: 8 Lines
Signal logic: Negative

True (low-level): 0.8V maximum

False (high-level): 2.OV minimum

r

4-l

SECTION 4
GPIB Interface

NRFD mot Ready For Data)

DIOI
D102
D103
D104

EOI

DAV
NRFD
NDAC

IFC

SRQ

ATN

SHIELD

I

Figure 4-1.

L Cab’e

fl

/

\ A Receptacle Side

IEEE-488

Interface Connector

D105
D106
D107
D108
REN
DAV GROUND
NRFD GROUND
NDAC GROUND

IFC GROUND
SRQ GROUND
ATN GROUND
LOGIC GROUND

This line indicates when listeners are ready to accept data
over the data lines.

NDAC (Not Dataxcepted)
This line indicates the acceptance of data by listeners.

Control Bus (ATN, REN, IFC, SRQ, EOI)

ATN UteNtion)
This line is an output line from the controller, and it indi-

cates whether the information on the data bus is to be in­terpreted as data or commands.

REN @emotemable>
This output line from the controller switches devices be-

tween remote control and local control.

IFC QnterFace clear)
This output line from the controller clears the interface of

active talkers and listeners.

4.1.3 Bus Line Signals and Operation

The GPIB bus consists of 24 lines, including eight data

lines, eight control lines, and eight signal/system ground

lines.

Data Bus (DIOl to DI08)

DIOl through D108 are the data input/output lines,
which are used to transfer both address and command in­formation (the type of data present on these lines is deter­mined by the ATN line). DIOl is the least significant bit

(LSB).

Handshake Bus (DAV, NRFD, NDAC)

These three lines are handshake lines used to ensure reli­able data transfer.

DAV @&a yalid)
This line indicates that the data on the DIO lines sent

from a talker or the controller are valid.

SRQ &en&e BeQuest)
This control line is used by a device to request service

from the controller. The controller detects this signal and
usually executes a serial or parallel poll operation.

EOI and QrJdentify)
This line is used to indicate the end of a multiple-byte

transfer sequence or, in conjunction with ATN, to execute
a parallel poll operation.

4.1.4 GPIB Handshaking

GPIB handshaking is performed by checking the status of
all the listeners and inhibiting the next data transfer until
all listeners have completed the reception of data, so that
the slowest device on the bus can perform data transfer
reliably. The handshaking operations are executed by the
following handshake line logic levels.

NRFD = High level: All listeners are ready for accepting

data.

DAV = Low level:

A talker has valid data on the data bus.

4-2

NDAC = High level: All listeners have completed data

reception.

8

0

SECTION4

GPIB Interface

Indicates that all listeners have completed data
input, and the bus is ready to transfer the next
data byte.

The handshaking timing diagram is in Figure 4-2. The
various timing points indicate the following:

Indicates that all listeners are waiting for data.

1

0

The talker places the data byte to be sent on the

2

0

0

0

data lines. Output may have already occurred.

The talker checks NRFD, and, if high, DAV is set

3

low to indicate to the listener that data is valid.

4 When DAV goes low, the listener reads data,

and NRFD is set low, indicating to the talker that
data processing is in progress. Each listener sets
NDAC high at the completion of data input. The
NDAC logic level is the result of ORing the
NDAC signals from each listener.

NRFD

(Listener) ‘0

DAV

(Talker)

NDAC

(Listener)

Data Bus

Signal

Fipure 4-2.

4.1.5

Figure 4-3 shows a a data transfer example using the

three-line handshake process. In this example, the char-

acter string “ABC” is sent, followed by the <CR> <LF>

delimiter.

Handshake Timina Diagram

Data Transfer Example

i II

i O!O

Valid Data

Ready for
next data byte

Data Bus Disabled
Data Bus Enabled

Termination of
Data Reception

Data not received
(in Data Reception)

5

0

6

0

7

0

When all listeners have completed receiving
data, NDAC goes high, indicating to the talker
that data reception has been completed.

The talker sets DAV high, indicating to the lis­tener that data on the bus is no longer valid.

The listener checks to see whether DAV is high
and sets NDAC low, completing the handshake.

4.1.6

* Only one talker may exist on the GPIB at a time.

l

Data is sent to listeners when the controller ATN line is
high (false).

l

Source handshaking is performed automatically.

l

A service request (SRQ) is sent to the controller by

other devices.

l

The talker function is available with both the local and
remote modes.

l

The talker function is canceled by any of the following:

When the talk address of another device is received.
When the device is addressed as a listener.
When the untalk (LINT) command is received.
When the interface clear (IX) command is received.

Basic Talker Functions

4-3

SECTION 4

GPIB Interface

DATA

ATN

DAV

NRFD

NDAC

1

UNL

Talker

Address

Listener

Address

A

B

C CR

LF

EOI

Figure 4-3.

Data Transfer Example

4.1.7 Basic Listener Functions

l

Two or more listeners may exist on the GPIB at any
time.

l

Data is received from a talker when the controller
ATN signal is high.

l

The acceptor handshake is performed automatically.

l

The listener function is canceled by any of the follow­ing:

When the device is addressed to talk.
When the unlisten (UNL) command is received.
When the IFC command is received.

4.1.8

l

Only one controller can be active on the GPIES.

Basic Controller Functions

* The controller sets the ATN signal to low to address

devices to listen and talk, and to transmit commands
such as DCL.

l

The controller sends single-line commands such as
KC and REN.

4.1.9

Multi-Line Interface Messages

A multi-line interface message is sent over the data lines

with ATN set low.

Table 4-1 summarizes these messages.

4-4

. . ,- + .--

I

----N<X~<C--,V,RC,V

I ?-

I

-Qe$fn* *-1 N 040

LISTENER ADDRESSES
ASSIGNED TO DEVICES

LISTENER ADDRESSES
ASSIGNED TO DEVICES

TALKER ADDRESSES

ASSIGNED TO DEVICES

TALKER ADDRESSES

ASSIGNED TO DEVICES

MEANING DEFINED BY PCG

II I

8

SECTION 4

GPIl3 Interface

4.2

OVERVIEW OF MODEL 3940 GPIB
INTERFACE

4.2.1

The Model 3940 GPIB interface has a wide variety of in­terface functions. These functions allow remote the set­ting of most of the parameters which can be set from the
front panel. The interface can also transfer setting data
and conditions to an external device, enabling the user to
easily configure a sophisticated, automatic measurement
system.

Setting data and conditions are sent to the controller as
character strings in ASCII format.

Introduction

4.2.2 Specifications

Interface Functions

Table 4-2 shows the interface functions of the Model

3940.

Bus Driver

Table 4-3.

DIOl to DIOB

NDAC, NRFD, SRQ

I

Codes

Codes which can be received by the Model 3940 in lis­tener mode are in 7-bit ASCII format (bit 7 is ignored).
Codes can be sent using either lower-case or upper-case

letters. In either case, codes are interpreted and executed

identically. The space (20H), tab (09H), null (OOH), and

semicolon “;” (3BH) are ignored.

Talker mode transmission codes are also in 7-bit ASCII
format. All letter characters are sent as upper-case letters.

GPIB Primary Address

The GPIB address of the Model 3940 is set by the front
panel GPIB key. Set values are stored in battery backed
up memory when the power is turned off. For details on
setting the primary address, in paragraph 3.2.1.

Bus Driver Specifications

Open Collector

I

DAV

EOI

I

3 state

Table 4-3 gives the bus driver specifications.

Table 4-2. Interface Functions

Function

Source Handshake
Acceptor Handshake
Talker
Listener
Service Request
Remote/Local
Parallel Poll
Device Clear

1 Subset 1 Explanation

SHl
AH1
T6
L4
SRl
RLl
PI?0
DC1
DTO
co

The factory default value for the primary address is 2.

I

Full source handshaking capability
Full acceptor handshaking capability
Basic talker, serial poll, talker unaddresses on MLA
Basic listener, unaddresses on MTA
Full service request capability
Full remote and local operation capability
No parallel-polling capability
Full device clear capability
No device trigger function capability
No controller function capability

SECTION4

GPlB Interface

Delimiter

The Model 3940 recognizes <CR>, <LF>, or cEOI> in any
combination as a delimiter for receiving code strings in
the listener mode.

The delimiter use when sending a code string in the talk­er mode is set from the front panel with the GPIB key.
Only <CR> or <CR><LF> can be selected as an output
delimiter, and EOI is sent simultaneously. For informa­tion on delimiter selection, in paragraph 3.2.1. The fac­tory default delimiter is <CR><LF> h EOI.

Response to Interface Messages

Table 4-4 summarizes Model 3940 responses to interface
messages.

Table 4-4. Responses to Interface Messages

IFC

Initializes GPIB interface
Releases specified listener and talker modes.

when an illegal header or parameter is found during the
interpretation of a program code. The input buffer is
similarly cleared and subsequent program codes are not
executed when errors other than the above occur during
the interpretation of a program code.

When interpretation and execution are completed, the in­put buffer is cleared, and the unit is ready to receive the
next program code.

As shown in Figure 4-4, program codes consists of a
header and a parameter. More than one program code
can be sent at a time, up to a maximum of 256 characters.
Multiple program codes can be separated by a space or
semicolon (;) to improve readability.

There are two general types of program codes: parame­ter-setting messages and inquiry messages. Parameter­setting messages are used for setting parameters or for
sending operating instructions. Inquiry messages are
used for requesting instrument state and parameter set­ting information.

DCL Clears GPIB input/output buffer.
and

Clears error status.

SDC Releases SRQ issuance and resets SRQ causes

(function of main unit remains unchanged).
LLO Disables front panel LOCAL key.
GTL Sets local mode.

Program Codes

Program codes used for the various settings of the Model

3940 are temporarily stored in the input buffer as re-

ceived. When a delimiter is received, they are interpreted
and executed in the order received. The input buffer can
store up to 256 characters (256 bytes). Note that space,
tab, null, semicolon, and delimiter characters are not
stored in the input buffer.

When a more than 256 program code characters are re-

ceived, the input buffer overflows. When an overflow oc­curs, the input buffer is cleared, and program codes
stored in the buffer are not executed.

In addition, the input buffer is cleared when a GPIB error
occurs, and subsequent program codes are not executed

SP : Space character

; : Semicolon character

Figure 4-4.

Parameter Setting Messages

The format of a basic setting

this example, the frequency is set to l.OkHz, and the

Program Code Syntax

message

is shown below. In

am-

plitude is set to l.OVp-p/no load.

a

*ii=-;

C-

beb a

cl

-@Y--;

C-

d

b e

a: Indicates the three-letter alphabetic character header.

Either upper-case or lower-case letters can be used.

b: Indicates a space character inserted for readability.

There is no limit on the number of spaces, and the
space can be omitted. Space, tab, null, and semicolon

characters are ignored and are not stored in the GPIB

input buffer.

4-7

SECTION 4

GPIB Interfaci

c:

Indicates the parameter mantissa. The mantissa in­cludes a polarity sign (space for +, or -), numeric
value, and decimal point. When the polarity sign is
omitted, the plus sign (+) is assumed. Parameters are
described in detail in the following paragraph.

d:

Indicates the exponent. Depending on the type of pro-

gram code, an exponent may not be included with the

parameter.

e:

Indicates the semicolon used to separate program
codes for readability. There is no limit on the number
of semicolons, and the semicolon can be omitted. The
semicolon is also ignored and is not stored in the GPlB
input buffer.

Numeric Format of Parameter-setting Messages

The three formats described below are used for the vari­ous parameter-setting messages.

Examples: +012.34

-50.0

1.8

NR3 Format
In the NIX3 format, numeric values are specified in expo-

nential form. The exponent character, E, and subsequent
sign and numbers can be omitted. When the exponent is

omitted, E+OO is assumed, and the value is handled as an

NR2 format parameter.

&DD.DD E-HDD

L

0 Leading zeroes and spaces are

ignored

0 Sign (+ for positive, - for nega-

tive, + is assumed if sign is

L

omitted).

0 Same as NR2 format.

NRl Format
In the NRl format, numeric values are specified as inte-

gers. No decimal point is used in this format. The decimal
point is assumed to be at the end of the last character.

+DDDD

Leading zeroes and spaces are ignored
Sign (+ for positive, - for negative; + is
assumed if sign is omitted).

Examples: +01234

-500
18

NR2 Format
In the NR2 format, numeric values are specified as real

numbers. NIX2 numeric values include a decimal point,

but digits to the right of the decimal point can be omitted.

Examples: +012.34E+03

-5O.OE-06
l.BE-09

Inquiry Messages

An inquiry message is a special program code with a
question mark (?) located at the beginning. An inquiry
message is used to request information from the instru­ment regarding a state or particular parameter setting.

Except for special cases, each inquiry message corre­sponds to an equivalent parameter-setting message. In­quiry messages include only the header and a question
mark; no parameters are used.

After receiving an inquiry message, the Model 3940
searches for the corresponding setting and places the re­sponse in its output buffer. When it is addressed to talk, it
sends that setting information to the controller.

4-8

* Leading zeroes and spaces are ignored
0 Sign (+ for positive, - for negative, + is

assumed if sign is omitted).

The response output format is the same as the format of

the corresponding setting message, as shown in Figure

4-5. The format for inquiries without corresponding mes-

sages are discussed below.

Figure 4-5.

Response Output Format

When more than one inquiry is sent to the Model 3940 at
the same time, only the last request is accepted, and pre­vious requests are ignored. When a new inquiry is re­ceived before the response for a previous request is com­pleted, the new request over-rides the previous request.

NOTES:

1. The header in the inquiry response string can be
turned on or off by sending the command “HDR 1”
or “HDR 0” respectively. The power-on default
header state is header on(“HDR 1”).

2. Either cCR><LF>*EOI or <CfiAEOI can be se­lected as the inquiry response delimiter. The delim­iter can be programmed with the front panel GJ?IB

key; see paragraph 3.2.1. The factory default delim­iter is cCRXLF>~EOI.

Numeric Format of Inquiry Message Response Parame­ters

As described below, three different formats are used for
inquiry response parameters.

NRl Inquiry Response Format

DDDD

l-

L

. Numeric digits.

Space indicates plus sign is assumed.

l

The plus sign is assumed for all NRl

l

format values except for the ARB for­mat readout.
Same as NR2 format.

l

Example: FNC 1

SECTION 4

GM3 Interface

NR2 Inquiry Response Format
In the NR2 format, inquiry response parameters are

specified as real numbers:

-BD.DD

l

I

Numeric digits with decimal point

l

Space represents plus, and minus
sign (-> indicates negative values.

l

The decimal point is always included.

l

The number of parameter characters
for each information item is fixed.

Example: DTY 25.0

(Indicates that the square-wave duty cycle is
set to 25%. Header: three characters, space
indicating sign: one character, numeric pa­rameter including decimal point: four char­acters. Total: eight characters.)

NR3 Inquiry Response

Format

In the NR3 format, parameters are specified in exponen­tial form:

_ DD.DD EkDD

L

l

Exponent (value is a multiple of

3).

* Value includes “E” character,

sign, and a two-digit value, for a
total of four characters.

L

l

Mantissa

l

Decimal point is adjusted so that

the exponent is a multiple of 3.

l

Space indicates positive value,
minus sign indicates negative
value.

l

Decimal point is always included

l

Number of parameter characters
for each information item are
fixed.

Example: STM l.OOOE+OO

(Indicates a one-second sweep time. Header:
three characters, space indicating sign: one
character, mantissa including decimal point:
five characters, exponent: four characters.

Total: 13 characters.)

(Indicates the output waveform is 2/.
Header: three characters, space indicating
sign: one character, numeric parameter: one
character. Total: five characters.)

ARB Waveform Write and Readout Operations

The ARB (arbitrary) waveform is defined by writing data
values between -511 and i-511 into Model 3940 address

4-9

SECTION4

GPIB Interface

memory locations 0 to 1023. Address locations 0 through

1023 correspond to one waveform period, while data val-

ues -511 through +511 define the waveform amplitude

(-511 corresponds to the negative peak value, and +511

represents the positive peak value of the waveform).

Waveform write and readout operations can both be per­formed using either ASCII or binary formats. Each of
these formats is discussed in the following paragraphs.

Waveform Write, ASCII Format

This format represents the various data elements as
ASCII numbers using the NRl format. Data elements are
separated by commas (,>.

When writing long data blocks, do not exceed 256 charac­ters (256 bytes). The waveform-programming process is
not affected by inserting the delimiter sequence during
data write, but it is necessary to insert the delimiter after
the programmed number of data characters have been
sent.

When a sequence of delimited program code that in-

cludes the “SET” command is received, the Model 3940
interprets subsequently bytes as binary data represent­ing waveform amplitude. The number of data words is
determined by the “WDN” command.

EOI will be ignored if asserted during the binary format

data write except on the last byte of binary data sent;--

Example:

EMT1 ; SlYI0 : WDN2 : SET<Delimiter>

Indicates start of data write.
Represents two-word data
write.
Starts write at address loca­tion 0.
Programs binary format
write.

Example:

EMT0 ; SIT100 ; WDN3cDelimiter>

Represents three-word data write.

L!

/

Indicates write to start at memory
location 100.
Indicates ASCII format

m +3.0. -5<Delimiter>

Represents the data: 3,0, and -5.

/

Indicates start of data write.

Waveform Write, Binary Format

The binary format represents the various data elements

as words of data, each of which is made up of two bytes in

2s complement format. Each data word is represented in

high-byte, low-byte order.

- Represents two-word data.
Last byte includes EOI.

Waveform Readout, ASCII format

The ASCII waveform readout format allows you read
back ARB waveform data as ASCII values. Waveform
data is sent back as four-character ASCII numbers. (“-” or
space, with three-character numbers), and is an identical
format to the NRl inquiry response format. Individual
data elements are separated with commas (,I.

The delimiter will be sent after each programmed block

of data is sent. The number of data elements per block is
specified with the ‘BLK” command.

The 256~character limitation that applies to ASCII

waveform write operations does not apply to ASCII
waveform readout. The number of data elements speci­fied with the “DWN” command can be transmitted in
one contiguous block.

4-10

SECTlON4

GPIB Inferface

Example:

FMTO ; SIT100 ; DWN3 ; m ; QUT<Delimiten

I

Programs data output

L

Specifies delimiter

L

Typical Response:

Waveform Readout, Binary Format

This format allows you to read back waveform data in bi­nary format, which is represented as two-byte words in
2s complement format. Data are transmitted in high­byte, low-byte order, and EOI is asserted with the last
byte of data.

Example:

FMT.1; SIT.100 ; DWN2 ; QYT<Delimiter>

Model 3940 Response:

-001, -OOO<Delimiter>

-002<Delimiten

Specifies start of
data output.

insertion.
Sets output to three
data elements.

I

Service Request (SRQ)

The Model 3940 can request service from the controller

via the SRQ line under the following conditions:

l

An error conditions occurs

l

A sweep stops

l

A sweep starts

l

Upon completion of calibration

When the controller detects an SRQ from the Model 3940
and performs a serial poll, the Model 3940 transfers the
status byte and clears the SRQ signal line (set high). Table
4-5 summarizes status byte conditions.

The status byte can be read using serial polling or by
sending “?STS”. When the status byte is read, the follow­ing bits are reset (cleared): bit 6 (RQS), bit 5 (error), bit 2
(SWEEP stop), bit 1 (SWEEP start), and bit 0 (Calibra­tion). Note, however, that corresponding masked SRQ
bits cannot be reset.

Bits in the status byte can be masked so that those particu­lar conditions willnot cause an SRQ to occur. To mask
bits, set the corresponding bits to 1 by adding up the deci­mal bit values and sending them with the “MSK” pro­gram code. For instance, to disable SRQ by masking the
SWEEP stop (bit 2), SWEEP start (bit l), and Calibration

(bit 0), send the command “MSK7” (22 + 2* + 2O = 7). When
these bits are masked, an SRQ will not occur at sweep
stop or sweep start, or during calibration.

I Represents two-byte word

data.
EOI asserted with last
byte.

Bit 7 (unused), bit 4 (HOLD), and bit 3 (SWEEP in execu­tion) cannot cause an SRQ. Therefore, setting or resetting
these bits has no effect on SRQ generation.

If SRQ is not masked, an SRQ is generated even when the
unit is in the LOCAL mode. At power-on, all SRQ condi­tions are masked (MSK 63). In addition, all SRQ causes
will be masked when DCL or SDC is received.

4-11

SECTION 4

GPIB lnferface

Table 45. Status Byte

Bit

WSB) 7

6

5

4

3

Description

0

RQS

Error (SRQ cause)

HOLD

SWEEP in execution

Set (1) Condition

(Unused, therefore always 0)

l

When SRQ is issued

l

When an error occurs

l

When sweep is stopped by “HOLD”

l

When sweep is started by sweep start

0 When sweep is restarted by releasing

“HOLD”

Reset (0) Condition

(Unused, therefore always 0)

l

When status byte is requested
with SRQ mask reset condition.

o When DCL or SDC is received

l

When SRQ cause is cancelled by
setting SRQ mask

l

When error code is requested
with “?ERR”

l

When status byte is requested
with SRQ mask reset condition

l

When DCL or SDC is received

0 When sweep is restarted by re-

leasing “HOLD’

l

When sweep is started during
HOLD

l

When sweep is turned off

l

When sweep is stopped due to
g end of single sweep or sweep

l

When sweep is stopped by
HOLD

2

1

(LSB) 0

SWEEP stop
(SRQ cause)

SWEEP start
(SRQ cause)

Calibration
(SRQ cause)

0 When sweep is stopped due to the end

of single sweep or sweep off

* When sweep is stopped by “HOLD”

l

When sweep is started by sweep start

l

When sweep is restarted by releasing

“HOLD”

l

When calibration is completed or
stopped

l

When status byte is requested
with SRQ mask reset condition

l

When DCL or SDC is received

l

When status byte is requested
with SRQ mask reset condition

l

When DCL or SDC is received

l

When status byte is requested
with SRQ mask reset condition

l

When DCL or SDC is received

412

SECTION 4

GPIB

Interface

Error Codes

Error codes indicate what kind of error has occurred. As
each error occurs, an error code is updated, and the latest
error information is always available. Error codes can be
read by sending the

“?ERR” inquiry. An error code is
cleared when read and when a DCL or SDC command is
received.

The status byte error bit (bit 5) is reset (0) when an error
code cleared. When an attempt is made to read an error
code by sending “?ERR” after the code is cleared,

Table 4-6. Main Synthesizer Parameter Setting Messages

Program Code

Function Header
H&EQUENCY

=Q

Parameter Operation and Setting Range

NR3

“ERROO” is returned to indicate that the error code has

been cleared.

Other returned error codes give the same information as
the corresponding display error codes, which are cov­ered in paragraph 3.5.3 in Section 3.

4.3 MODEL 3940 PROGRAM CODES

4.3.1

Model 3940 Parameter-Setting
Messages

Inquiry

Oscillation frequency setting

(frequency: Hz)
Range: 0 (OHz) to 25.0E+06 (25MHz)
Resolution: O.lE-03 (O.lmHz)
Example: FRQ l.OE + 2 (1OOHz)

YES

IPENOR

PRD NR3

Sets oscillation frequency by period

(period: s)
Range:

4O.OE-09 (OHz) (40ns=25MHz)

to lO.OE+03 (1OOOOs=O.lmHz)
Resolution: lE-09 (Ins)

PRD l.OE + 00 (ls=lHZ)

AlYPLIl-UDE
yp-p/OPEN

NR3

Example:
Sets output amplitude (VP-p/no load)

Range: 2.00E-03 (2mVp-p/no load) to

20.OE+OO (20Vp-p/no load)
Resolution: O.OlmVp-p/no load
Example:

AMV 2.OE 0 (2Vp-p/no load)

BMpLITUDE TERMINATE ATV NR3 Sets output amplitude (VP-p/5OQ)
Yp-p/5OQ

Range: l.OOE-03 (ImVp-p/5Ofi) to

lO.OE+OO (lOVp-p/Son>
Resolution: O.OlmVp-p/SOsZ
Example: ATV 1E + 0 (lVp-p/5OQ)

Yes

Yes

Yes

4-13

SECTTON 4

GPIB Interface

Function

Main Synthesizer Parameter Setting Messages (Cont.)

Program Code

Header

Parameter Operation and Setting Range

Inquiry

AM.l?LITUDEVrms/OPEN

BMpLITUDETjERMINATE

&ms/5OQ

ATR

NR3

NR3

Setsoutputamplitude(Vrms/noload)
Range: For% : 0.71E-03

(0.7lmVrms/noload) to

7.07E+OO (7.07Vrms/noload)
Forz/ ,A ,\ : 0.58E-03
(0.58mVrms/noload) to

5.77E+00(5.77Vrms/noload)
For n :l.OOE-O3
(l.OOnVrms/noload)to

10.OE+00(10.OVrms/noload)
Resolution: O.OlmVrms/noload
Example: AMX6.2E+0 (6.2Vrms

/noload)

Setsoutputamp. de(Vrms/500>

Range:

For

%

: 0.36E-03

(0.36mVrms/50Q)to

3.53 +00(3.53Vrms/50R)

For

, n ,\:0.29E-O3

t/

(0.29mVrms/50Q)to

2.88E+00(2.88Vrms/50Ci)

For k : 0.50E-03
(0.50mkns/50Q)to

5.00E+00(5.00Vrms/50d)
Resolution: O.OlmVrtns/50Q
Example:

ATR3.10E+00(3.1Vrms/50Q)

Yes

Yes

&jJ?LITUDE~BV/Ol?EN

&Ml?LITUDE~RMINATE
JBV/50R

ATD

NIX3

NR3

Setsoutputamplitude(dBV/noload)
Range:

For% :-63.OE+OO
(-63.0dBV/noload)to

16.9 +00(16.9dBV/noload)

For

n, y :-64.7E+oo

4/

(-64.7dBV/noload)to

15.2E+OO (15.2dBV/noload)

Fork :-6O.OE-O0
(-dO.OdBV/noload)to

20.OE+00(20.0dBV/noload)
Resolition: O.ldBV/noload
Example:

AMD-6.2E+OO
(-6.2dBV/noload)

Setsoutputamplitude(dBV/50!.2)
Range:

For 2/:-69.OE+OO
(-69.0dBV/50J;Z)to

10.9E+00(10.9dBV/50~)

For\, /l , \ :-70.7E+OO
G70.7dBV/50Q)to

9.2E+00(9.2dBV/50Q)

For k :-66.OE+OO
(-66.0dBV/50Q)to

13.9E+00(13.9dBV/50Q)

Resolution: O.ldBV/50Q
Example:

ATD-10.2(-10.2dBV/50Q

Yes

Yes

4-14

Main Synthesizer Parameter Setting Messages (Cont.)

Program Code

Function Header Parameter

SECTION 4

GPIB Interface

Operation and Setting Range Inquiry

WLITUDE TERMINATE ATM

NIX3

dB&50Q Range:

Sets output amplitude (dBm/50fi) Yes

For 2/ : -56.OE+OO
(-56.0dBm/50Q) to

23.9E+OO (23.9dBm/50Q)
For\, n ,A : -57.8E+OO
(-57.8dBm/50R) to
po!EiOO (22.2dBm/50Q)

: -53.OE+OO

(-53.0dBm/50Q) to

26.9E+OO (26.9dBm/50Q)

Resolution: O.ldBm/EiOfi

ATM 0.2E+OO (0.2dBm/50R>

-lO.OE+OO (-lOV/no load) to

OFFSET

Example:

OFS NR3 Sets DC offset voltage (V/no load)

Range:

lO.OE+OO (lOV/no load)

Resolution: O.OlmV/no load

OFS 4.5E-1 (0.45V/no load)

-5.OOE+OO (-5V/5OQ) to

Q&SET TERMINATE OFT

NR3

Example:
Sets DC offset voltage (V/SOsZ)

Range:

5.00E+OO (5V/5Oa)
Resolution: O.OlmV/5OsZ
Example: OFT 0.25 (0.25V/5OsZ>

WXION FNC NRl Selects output waveform

Range: 0 to 6
0:
1:

c

2:
3:
4:

8

A

5:
6:
Example:

xl3

muC1(2/)

Yes

Yes

Yes

MODE

MOD

NRl

Sets oscillation mode YeS
Range:
0:

0 to 3

CONT (Continuous)
1: BRST (Burst)
2:

TRIG (Trigged

3: GATE
Example:

MOD 0 (CONT)

4-15

SECTION 4

GPIB Interface

Function

Table 4-7. Sub Synthesizer Parameter Setting Messages

Program Code

Header

Parameter Operation and Setting Range

Inquiry

SUB SYNTHESIZER
FREQUENCY

SUB SYNTHESIZER
PERIOQ

SUB SYNTHESIZER
A,MPLITUDE yp-p/OPEN

SUB SYNTHESIZER
MLITUDE Vrms/QPEN

SFR

SBD NR3

SAV NR2

SAR NIX3

Sub synthesizer oscillation frequency set­ting (frequency: Hz)
Range:

0 (OHz) to lOO.OE+03 (1OOkHz)
Resolution: O.lE-03 (O.lmHz)
Example:

SFR l.OE + 3 (11612)
Sub synthesizer oscillation frequency set-

iing (period: s)
Range:

lO.OE-06 (lOms=lOOkHz) to

lO.OE+03 (1OOOOs=O.lmHz)
Resolution: O.lE-06 (1OOns)
Example: SBD 1E + 2 (lOs=O.OlHz)

Sets sub synthesizer output amplitude
(VP-p/no load)
Range: 0.2 (0.2Vp-p/no load) to

20.0 (20Vp-p/no load)
Resolution: O.lVp-p/no load
Example: SAV 5.OE + 00 (5Vp-p/no load)

Sets sub synthesizer output amplitude
(Vrms/no load)
Range: For 2/ : O.l(O.lVrms/no load)

to 7 0 (7.0Vrms/no load)
For& n ,\ : O.l(O.lVrms
no load)

to 5.7 (5.7Vrms/no load)
For k : O.l(O.lVxms/noload)
to 10.0 (lOVrms/no load)

Resoltution: O.lVrms/no load

Example: SAR 6.2E+O (6.2Vrms/no load)

Yes

Yes

Yes

Yes

SUB SYNTHESIZER
&Il?LITUDE BV/OPEN

4-16

SAD

Sets sub synthesizer output amplitude

(dBV/no load)

Range: For 2/ : -23.0 (-23.0dBV/

no load) to

17.0dBV/no load)

17.0

For

A , \ :-24.7

It

(-24/7dBV/no load) to

15.2dBV/no load)

15.2

Ic

For

: -20.0 (-20.0dBV/

no load) to

20.0 (20.0dBV/ no load)
Resolution: O.ldBV/no load
Example: SAD -2.3E+OO

G2.3dBV/no load)

Yes

Function

Sub Synthesizer Parameter Setting Messages (Cont.)

Program Code

Header Parameter Operation and Setting Range

SECTlON 4

GPIB

Interface

%uiry

$J&SYNTHESIZER

-FUNCTION

SUB SYNTHESIZER
EWE

SBF NRl

SEW NR2

Selects sub synthesizer output waveform
Range: 1 to5
0:
1:
2:
3:

T

I-L

4:
5:

4

Example: SBF2( ‘+\ )
Sets sub synthesizer phase (‘7 deg)

Range: -360.0 to 360.0

(-360”

to 360”)

Resoltuion: 0.1”
Example: SPH 180.0 (180”)

Yes

Yes

Yk

4-17

Function

Table 4-8. Main Synthesizer Trigger

Program Code

Header

Parameter

Parameter Setting Messages

Operation and Setting Range Inquiry

TRIGGER SOURCE

REMOTE TRIGGER

STOP LEVEL

TRS NRl

NRl

NRl

Selects trigger source

Yes
Range: 0 to 3
0: EXT%
1: EXT.!K
2: INTX
3: INTJ
Example: TRS 2 (triggered by% of INT

Yes

TRIG GEN)

Function equivalent to panel MAN key Ef- Yes
fective only when trigger source is EXT

(Burst: Trigger is performed when TRG 0
changes to TRG 1
Gate: Gate off when TRG 0 is specified. Gate
on when TRG 1 is specified)
Range:

0 or 1

0: Trigger inactive (Equivalent to

MAN key off>

1: Trigger active (Equivalent to

MAN key on)

Example: TRG 1
Selects stop level

Yes
Range: Oorl
0: HOLD

1:

Example:

RESET
SPL 1

VISCOUNT

SPACE COUNT

PHASE

@SYNC

NR2

NE2

None

Sets number of mark cycles (cycle) Ye.5
Range: 0.5 to 32768.0
Resolution: 0.5 cycle
Example: MRK 10 (10 cycles)

Sets number of space cycles

Yes
Range: 0.5 to 32768.0

Resolution: 0.5 cycle
Example: SK 12.5 (12.5 cycle)

Sets phase (“: deg) Yes

Range: -360.0 to 360.0 (-360” to 360”)
Resolution: 0.1”
Example:

PHS 270.0 (270”)

Performs phase sync No
Example: SYN

Function

Main Synthesizer Trigger Parameter Setting Messages (Cont.)

Program Code

Header Parameter Operation and Setting Range

SECl7ON 4

GPIB Inferface

Inquiry

FXTI&IGIN

BNC ENABLE

TRE NRl Enables EXT TRIG IN connector on front

panel in remote mode. (This function be­comes effective when trigger source is EXT
and TRE 1 is received. In local mode, it is
always effective. When remote mode is set
again, status of previous remote mode is
effective. TRE 1 is set at initial state when
power is turned on, or when PST command
is executed.)
Range: Oorl
0: In remote mode, EXT TRIG IN

connector is disabled.

1: In remote mode, EXT TRIG IN

connector is enabled.

Example: TIRE 1

Yes

4-19

SECTION 4

GPIB

Inferface

Function

Table 4-9. Main Synthesizer Sweep Parameter Setting Messages

Program Code

Header

Parameter

Operation and Setting Range

Inquiry

SWEEP START

l3EQUENC-Y

SWEEP START
PERIOD

SWEEP STOE
WQUENCY

SWEEP STOP
PERJOB

SWEEP CENTER

EF=QuENcY

STF

3-D

NR3

NR3 Sets sweep start frequency by period

SPF NR3

SPD NJ33

CTF

NR3 Sets sweep center frequency (Frequency: Yes

Sets sweep start frequency (Frequency: Hz)

Yes

Range: O.OE+OO (OHz) to

25.0E+O6 (25MHz)
Resolution: O.lmHz
Example: STF l.OE+2 (1OOHz)

Yes

(period: s)

Range: 4O.OE-09 (40ns=25MHz) to

lO.OE+03 (1OOOOs=O.lmHz)
Resolution: Ins
Example:

STD l.OOE+O (ls=lHz)

Sets sweep stop frequency (Frequency: Hz) Yes
Range: O.OE+OO (OHz) to

25.0E+06 (25MHz)
Resolution: O.lmHz
Example:

SPF l.OE+2 (1OOHz)

Sets sweep stop frequency by period Yes

(period: s)

Range:

40.OE-09 (40ns=25MHz to
lO.OE+03 (1OOOOs=O.lmHz)

Resolution: Ins
Example:

STD l.OE+O (ls=lHz)

Hz)
Range:

O.OE+OO (OHz) to

25.0E+06 (25MHz)

Resolution: O.lmHz
Example:

CTF LOE+2 (1OOHz)

SWEEP CENTER
PENOR

SWEEPZI’~

FEQUENCY

4-20

CTD

SNF

NE3 Sets sweep center frequency by period

(Period: s)
Range:

40.OE-09 (40ns=25MHz) to
lO.OE+O3 (10000s=O.lmHz)

Resolution: Ins

CTD 1.0000 (ls=lHz)

NR3

Example:
Sets sweep frequency span (Frequency: Hz)

Range: O.OE-03 (0 Hz) to

25.0E+06 (25MHz)

Resolution: O.lmHz
Example:

SNF l.OE+2 (1OOHz)

Yes

Yes

Function

Main Synthesizer Sweep Parameter Setting Messages (Cont.)

Program Code

Header Parameter

Operation and Setting Range

SECTION4

GPIB Interface

Inquiry

SWEEP SI’M
PERIOD

SWEEPWRKER

FEQU='J-

SWEEP-&WXER
PERIOD

CENTER FROM -WR

SND

NIX3

NR3

NR3

CFM None

NIX3

Sets sweep frequency span by period
(period: s)
Range:

4O.OE-09 (40ns=25MHz) to

lO.OE+03 (10000s=0.1mHz)
Resolution: Ins
Example:

SND 1 (ls=lHz)
Sets sweep marker frequency

(Frequency: Hz)
Range:

O.OE+OO (OHz) to

25.0E+06 @MHz)
Resolution: O.lmHz
Example:

MKF l.OE+2 (1OOI-W

Sets sweep marker frequency by period
(period: s)
Range:

40.0E-09 (40ns=25MHz) to

lO.OE+03 (1OOOOs=O.lmHz)
Resolution: 1 ns
Example:

MKD l.OE+OO (ls=lHz)
Assigns marker frequency to center fre-

quency.

(Assigns marker period to center period.)

Sets sweep time (s)
Range:

5.OE-03 (5ms) to

9.999E+03 (9999s)
Resolution: lms
Example:

STM l.OE+OO (1s)

Yes

Yes

YC!S

No

YC!S

WEEP CONTWOUS
START

SWEEP SINGLE
START

SCN

SSG

NRl

Selects sweep function
Range: 0 to 4

None

0:

1:
2:
3:
4:

Example:

Disables sweep

J-

LIN A
LIN /j

LOG A
LOG/l
SFN2(LIN/l )

None Starts continuous sweep

None Starts single sweep

YC!S

No
No

No

4-21

SECTION 4

GPIB Inferface

Function

Main Synthesizer Sweep Parameter Setting Messages (Cont.)

Program Code

Header

Parameter Operation and Setting Range

Inquiry

WEEP STAR1 STATE

SST

None Outputs start frequency

SWEEP STOP STATE SSP None

$INGL START IN BNC

HLD
RSM

SGE

None
None

NRl

ZNABLE

No

(When this command is issued during
sweep, sweep is stopped, and start fre­quency is output.)

Outputs stop frequency

No

When this command is issued during
sweep, sweep is stopped, and stop fre­quency is output.)

Halts sweep No
Restarts sweep.

No
(Even when RSM command is issued in
other than HOLD state, it is ignored and not
treated as an error.)

Enables SINGL START IN connector on rear

Yes
panel in remote mode (In local mode, it is
always enabled. When remote mode is set
again, status of previous remote mode is
effective. SGE 1 is set when power is first
turned on, or when PST command is exe­cuted.)
Range: 0 or 1
0:

In remote mode, SINGL
START IN connector is dis­abled.

1:

In remote mode, SINGL
START IN connector is
enabled.

Example: SGE 1

ZOLD IN BNC ENABLE

HLE

NRl

Enables HOLD IN connector on rear panel

Yes

in remote mode. (In local mode, it is always
enabled. When remote mode is set again,
status of previous remote mode is effective.
HLE 1 is set when power is first turned on,
or when PST command is executed.)
Range:
0:

0 or 1
In remote mode, HOLD IN
connector is disabled.

1:

In remote mode, HOLD IN
connector is enabled.

Example:

NOTE: When the HOLD JN connector is enabled, the relationship between HOLD IN and the HLD or FGM command is as follows:

1. When the HOLD signal is applied to HOLD IN (low), the HLD and RSM commands have no effect. The sweep starts when the HOLD IN
signa goes high.

2 While a sweep is halted by the HLD command, the HOLD IN connector is disabled. The sweep restarts when the RSM co&and is issued.

HLEO

4-22

Function

Table 4-10. Miscellaneous Parameter Messages

Program Code

Header

Parameter Operation and Setting Range

SECTION4

GPIB Inferface

Inquiry

Dm- CYCLE

QU’IX CYCLE ED(ED

DTY NR2

DYE None

VIBRATION CAL None

CALIBRATION BORT

ml? ON/OFF

MEMORY STORE

MEMORY @CALL

CAB

BEE

ST0

RCL

None

NRl

NRl

NRl

Sets square wave duty cycle (o/o)
Range:

5.0 to 95.0 (5.0% to 95.0%)
Resolution: 0.1%
Example:

DTY 12.5 (12.5%)

Sets square wave duty cycle at 50% (fixed)
Example: DYE

Performs’main synthesizer output ampli­tude calibration
Example: CAL

Aborts main synthesizer output amplitude
calibration
Example: CAB

Selects beep sound ON/OFF
Range: Oorl
0: OFF

1: ON
Example: BEE 1 (beep sound ON)

Stores setting conditions in memory.
Range: 0 to 9 (Memory number)
Example: ST0 1

Recalls setting conditions from memory.
Range:

0 to 9 (Memory number)

Example: RCL 9

Yes

No

No

No

Yes

No

No

DIspLAY

SUB SYNTHESIZER
DI$l?LAY

FCTN SIGNAL ON/OFF

PANEL KEY Loa
ON/OFF

PWSEL

DSP

SDP

SIG

LCK

PST

None

None

NRl

NRl

None

Displays main synthesizer main parameters.

No

Example: DSP
Displays sub synthesizer main parameters.

No

Example: SDP
FCTN OUT on/off (turns output on/off)

Yes
Range: Ooil
0: OFF

1: ON

Example: SIG 1 (signal output ON)
SOe$!;&hibition of panel key setting

Yes

Range: 0 or 1
0: OFF (keys enabled)
1:

ON (keys disabled)

Example: LCK 1 (keys disabled)
Sets preset mode. No

Example:

PST

4-23

SECTION 4

GPIB

h’nterface

Function

Table 4-11. ARB Waveform Write and Readout Messages

Program Code

Header Parameter Operation and Setting Range

Inquiry

FOWI

NRl

Selects ARB waveform write and readout Yes
format
Range: Oorl
0: ASCII format
1:

Binary for&at

Example: FMT 1

START ADDRESS

STT

NRl Sets start ARB waveform write and readout Yes

address
Range: 0000 to 1023
Example: STTO

(Starts from address 0 for write
or readout of ARB waveform.)

WORD &I-UMBER

WDN

NRl Number of words for ARB waveform write Yes

and readout to be conducted
Range: 0001 to 1024
Example: WDN 1024

(Performs 1024 words of ARB
waveform write and readout
from start address specified by
STT command)

WAVEFORM= SET None Starts ARB waveform write

Example: SET

OUTPUT &Oa SIZE BLK

NRl Number of words per block for ASCII for-

mat ARB waveform readout
Range: 0001 to 1024
Example BLK 0512

(Performs 1 block of ARB
waveform readout totalling
512 words)

No

Yes

WAVEFORM~UT OUT None Starts ARB waveform readout

Example: OUT

4-24

No

Table 4-12. Parameters Specific to GPIB

SECTION 4

GPIB Inferface

Function
BAQEE ON/OFF

3RQ &L%SK

Program Code

Header

HDR

MSK

Parameter

NRl

NRl

Operation and Setting Range
Selects inclusion

of header in inquiry mes- Yes
sage response.
Range:
0:

0 or 1
No header is included in
inquiry message response (off).

1:

Example:

Header is included in inquiry

message

response (on)

HDR 1

Sets SRQ mask.
Range:
32:

00 to 63

Error occurred. (32: error SRQ

0: No Error SRQ)
16:
8:

4:

No effect (same as 0)

No effect (same as 0)

SWEEP stop (4: SWEEP stop.
0: No SWEEP stop.)

2:

SWEEP start (2: SWEEP start.
0: No SWEEP start.)

1:

Calibration is completed.
(1: Calibration is completed.
0: Calibration is not com-

pleted.)
Total of above SRQ causes is masked.
Example:

MSK 6

(6=4+2: SRQ is not issued

when SWEEP

stops

or starts.)

Inquiry

Ye.5

4-25

SECTION

4

GPIB Interface

4.3.2

Model 3940 Inquiry Messages

When the header is on (HDR l), each inquiry response
will include a three-character identifying mnemonic.

When the header is off (HDR 0), the first mnemonic not

Table 4-13. Main Synthesizer Parameter Inquiry Messages

Program

Inquired Item
FREQmN-

Code Response Format Setting

?FRQ

Oscillation frequency (frequency: Hz)

EUWQ

?l?RD

Oscillation period (period: s)

sent, and only the parameter itself is transmitted. Each
parameter begins with a space or minus sign (-) to indi­cate polarity.

NR3 format: Yes

Mantissa: 12 digits
Exponent: 2 digits

Example: FRQ 01.0000000000E+06

(1MI-m

NIX3 format:

Yes
Mantissa: 6 digits
Exponent: 2 digits

Example: PRD 3.33333E-03

(3.33333ms=3OOHz)

iikD-‘LmE @p-p/OPEN

Output amplitude (VP-p/no load)

AMPLITUDE ~RMINATE @p-p/5OQ)

Output amplitude (VP-p/5Ofi)

MLITUDE (Vspls/Ol’EN)
Output amplitude (Vrms/no load)

&WLlTUDE TERMINATE (Vsms/50&2)
Output amplitude (Vrms/50R)

&Q’LITUDE (sBV/OPEN)
Output amplitude (dBV/no load)

?AMV

NR3 format: Yes

Mantissa: 3 digits
Exponent: 2 digits

Example: AMY lO.OE+OO

(lOVp-p/no load)

?ATV NR3 format: Yes

Mantissa: 3 digits

Exponent: 2 digits

Example:

ATV 5.OE+OO

wp-p/mm

?AMR NR3 format: Yes

Mantissa: 3 digits
Exponent: 2 digits

Example:

AMR 1.23E+OO
(123Vrms/no load)

?ATR

NR3 format: Yes

Mantissa: 3 digits
Exponent: 2 digits

Example:

ATR 0.62E+OO
(0.62Vrms/50R)

?AMD NR3 format: Yes

Mantissa: 3 digits
Exponent: 2 digits

Example: AMD Ol.OE+OO

(ldBV/no load

4-26

Main Synthesizer Parameter Inquiry Messages (Cont.)

SECTSON 4

GPIB In

terfuce

Inquired Item

_AMPLITUDE TERMINATE @BV/5OQ)
Output amplitude (dBV/50Q)

MPLITUDE TERMINATE (dB&50R)
Output amplitude (dBm/50Q

OFESET

DC offset

voltage

(V/no load)

-ET IERMINATE
DC offset voltage (V/5OQ2)

Program

Code

?ATD

?ATM

?OFS

?OFr

Response Format

NR3 format:

Mantissa: 3 digits
Exponent: 2 digits

Example:

ATD -07.OE+OO

(-7dBV/50R)

NR3 format:

Mantissa: 3 digits
Exponent: 2 digits

Example:

ATM -12.4E+OO
(-12.4dBm/50SL)

NR3 format:

Mantissa: 3 digits

Exponent: 2 digits

Example:

OFS -12.3E+OO
(-12.3V/no load)

NIX3 format:

Mantissa: 3 digits
Exponent: 2 digits

Example:

OFT -18.3E+OO

(-18.3V/5OQ)

Setting

YES

Yes

YeS

YeS

=TION
Output waveform

MODE

Operating mode

?FNC

?MOD

NIXI format:

One digit, same as setting value.

Example: FNC 1 ( 2/ )
NIX1 format:

One digit, same as setting value.

Example: MOD 1 (BRSTI

Yes

Yes

4-27

SECTION 4

GPIB In tsrface

Inquired Item

Table 4-14. Sub Synthesizer Parameter Inquiry Messages

Program

Code

Response Format

Setting

SUB SYNTHESIZER mEQUENCY
Sub synthesizer oscillation frequency

(frequency: Hz)

SHE SYNTHESIZER PERIOQ
Sub synthesizer oscillation period (period: s)

SUB SYNTHESIZER AlvB?LlTUDE &p-p/OPEN)
Sub synthesizer output amplitude (VP-p/no load)

SUB SYNTHESIZER AM.l?LIT’UDE (Vps/Ol?EN)
Sub synthesizer output amplitude (Vrms/no load)

SUB SYNTHESIZER AMPLITUDE @VB/OPEN)
Sub synthesizer output amplitude (dVB/no load)

~~SYNTHESIZERWNCTION
Sub synthesizer output waveform

?SFR

?SBD

?SAV

?SAR

?SAD

?SBF

NR3 format:

Mantissa: 10 digits
Exponent: 2 digits

Example:

SIR 1OO.OOOOOOOE+O3

(1OOkHz)

NR3 format:

Mantissa: 6 digits
Exponent: 2 digits

Example: SBD 3.33333E-03

(3.33333ms=300Hz)

NR2 format:

Mantissa: 3 digits

Example:

SAV 10.0 (lOVp-p/no load)

NIX2 format:

Mantissa: 3 digits

Example: SAR 1.23

(1.23Vrms/no load)

NR2 format:

Mantissa: 3 digits

Example:

SAD 01.0 (ldVB.no load)

NM format:

One digit, same as setting value.

Example:

SBF 2 ( 2/ )

Yes

Yes

Yes

Yes

YeS

Yes

SUB SYNTHESIZER =SE
Sub synthesizer phase (“: deg)

4-28

?SPH

NR2 format:

Mantissa: 4 digits

Example:

SPH 1180.0 (-180.0’)

Yes

Inquired Item

Table 4-15. Main Synthesizer Trigger Parameter Inquiry Messages

Program

Code

Response Format

SECTlON 4

GPIB Inferface

Setting

I

mGGER SouncE

Trigger source

REMOTE TRIGGER
Whether or not remote trigger is active

STOz LEVEL

Stop level

MA&K COTJNT
Mark wave cycles (cycles)

SpACE COUNT
Space wave cycles (cycles)

l%?tif%E
Phase (“: deg)

EXT TBrG IN BNCENABLE
Inquiry on whether EXT TRIG IN connector on
the front panel is enabled or not in remote mode

?TRS

?TRG

?SPL

?M-RK

?SPC

?l?HS

?TRE

NRl format:

One digit, same as setting value.

Example:

TRS 2 (INT x )

NRl format:

One digit, same as setting value.

Example: TRG 0
NRl format:

One digit, same as setting value.

Example:

SPL 0 (HOLD)

NR2 format:

Mantissa: 6 digits

Example:

MRK 00128.0 (128 cvcles)

NR2 format:

Mantissa: 6 digits

Example:

SPC 00063.5 (63.5 cycles)

NR2 format:

Mantissa: 4 digits

Example:

PHS -270.0 (-270.0”)

NRl format:

One digit, same as setting value.

Example:

TRE 1 (Enabled)

YeS

YeS

Yes

Yes

Yes

Yf3.S

YeS

4-29

SECTION 4

GPIB Interface

Table 4-16. Main Synthesizer Sweep Parameter Inquiry Messages

[nquired Item

WEEPSTART EREQUENCY
Sweep start frequency (frequency: Hz)

WEEP STAm PERIOQ
Sweep start period (period: s)

?%‘EEP STOP =QTJENCY
Sweep stop frequency (frequency: Hz)

WEEP STOP PERIOD
sweep stop period (period: s)

Wv’EEP~~R-FREQUENCY
sweep center frequency (frequency: Hz)

Program

Code Response Format

?STF NR3 format:

Mantissa: 12 digits
Exponent: 2 digits

Example: STF00100.0000000E+03 (1OOkHz)

?STD

NR3 format:

Mantissa: 6 digits
Exponent: 2 digits

Example:

STD 3.33333E-03
(3.33333ms=3OOHz)

?SPF NR3 format:

Mantissa: 12 digits
Exponent: 2 digits

Example: SPF 01.0000000000E+06 (1MHz)

?Sl?D

NR3 format:

Mantissa: 6 digits
Exponent: 2 digits

Example: SPD 3.33333E-03

(3.33333ms=3OOHz)

?CTF NR3 format:

Mantissa: 12 digits
Exponent: 2 digits

Example:

CTF 00100.00000OOE+03 (1OOkH.z)

Setting

Yes

Yes

Yes

Yes

Yes

SWEEP c=R PERIOD
Sweep center period (period: s)

SWEEPZAbJEREQUENCY
Sweep span frequency (Frequency: Hz)

SWEEP sl?m PERIOD
Sweep center period (period: s)

SWEEP -R WQUENCY
Sweep marker frequency (Frequency: Hz)

4-30

?CTD NR3 format:

Mantissa: 6 digits
Exponent: 2 digits

Example:

?SNF NR3 format:

Mantissa: 12 digits

Exponent: 2 digits

Example:

?SND NR3 format:

Mantissa: 6 digits

Exponent: 2 digits

Example: SNJI 3.33333E-03

?MKF

NR3 format:

Mantissa: 12 digits
Exponent: 2 digits

Example: SNF 00100.0000000E+03 (1OOkHz)

YC!S

CTD 3.33333E-03

(3.33333ms=300Hz)

Yes

SNF 01.0000000000E+06 (1MHz)

Yes

(3.33333ms=300Hz)

Yes

Inquired Item

Main Synthesizer Sweep Parameter Inquiry Messages (Cont.)

Program

Code

Response Format Setting

SECTION 4

GPIB Interface

SWEEP J&XRKBR J?BRIOQ
Sweep marker period (period: s)

2W=P D&G
Sweep time (s)

SWEEPmCTION
Sweep function

SINGL START IN BNC IENABLE
Whether or not SINGL START IN connec-

tor on rear panel is enabled in remote
mode

HOLD IN BNC ENABLE

Whether or not HOLD IN connector on

rear panel is enabled in remote mode

?MFD

NR3 format: Yf?S

Mantissa: 6 digits
Exponent: 2 digits

Example:

SND 3.33333E-03

(3.33333ms=300Hz)

?STM NR3 format:

YES
Mantissa: 4 digits
Exponent1 2 digits

?SFN

Example:
NRl format Yes

STF 1.234E+OO (1.234s)

1 digit, same as setting value.

?SGE

Example:
NRl format:

SFN 1 (LIN n >

Yes

1 digit, same as setting value.

Example:

SGE 1 (Enabled)

?HLE NRl format: Yes

1 digit, same as setting value.

Example: HLE 0 (Disabled)

4-31

SECTION 4

GPIB Interface

Table 4-17. Inquiry Messages for Miscellaneous Parameters

Inquired Item

I

DU- CYCLE
Square wave duty cycle (%)

QUTXYAWn<D
Inquiry on whether square wave duty cy-

cle is variable or fixed at 50%

ml’ ON/OFF
Beep signal ON/OFF

FCTN OUT sK;NAL ON/OFF
Signal output ON/OFF

PANEL KEY LOa ON/OF’!?
Panel key lock ON/OFF

Program

Code

I

?DTY

?DYV NRl format:

?BEE NRl format:

?SIG NRl format:

?LCK NRl format:

Response Format

I

NR2 format:

Mantissa: 3 digits

Example: DTY 25.0 (25%)

1 digit ’

0:

1: Variable

Example: DYV 1 (Variable)

1 digit, same as setting value.

Examule: BEE 0 (OFF)

1 digit, same as setting value.

Example: SIG 1 (ON)

1 digit, same as setting value.

Examule: LCK 1 (ON)

Setting
Yes

Yes

Fixed 50%

YeS

Yes

YeS

4-32

SECTION 4

GPIB Interface

Table 4-18.

Inquiry Messages for ARB Waveform Write and Readout Parameters

Inquired Item

EOU!DU

ARB Waveform write or readout formats

START ADDRESS
ARB Waveform write or readout address

W0R.Q -ER
ARB Waveform write or readout word

0uTl?uT~0C~SIzE
Number of words for one block with
readout of ARB waveform in ASCII for­mat

Program

Code

?FMT

Response Format
NRl format:

1 digit, same as setting value.

Example: FMT 1 (Binary)

?STr

NRl format:

4 digits, same as setting value

Example: STT 0000

?WDN

NR1 format:

4 digits, same as setting value.

Example: WDN 1024

?BLK NRl format:

4 digits, same as setting value.

Example: BLK 0128

Setting
YC?S

Yes

(Starts write and readout from 0
address.)

Yes

Performs 1024 words of write and

readout)

Yes

(Performs 1 block of ARB
waveform readout totaling 128
words)

4-33

SECTION 4

GPIB Interface

Table 4-19. Inquiry Messages for Parameters Specific to GPIB

Inquired Item
IiIW-BE ON/OFF

On/off state of header in inquiry message
response

SRQ -ltfAiX
SRQ mask setting

(See Service Request in Section 4.2.2
Specifications)

$XATU$ BYTE
Status byte readout

=OR STATUS
Error number readout

(See (15) Error Cord in Section 7.2.2 Speci-

fications)

UNIT ~EN~IFICATION

Program

Code

?HDR

?MSK

?STs

?ERR

?IDT

Response Format

NRl format:

1 digit, same as setting value.

Example: HDR 1 (on), 0 (off)
NRl format:

2 digits, same as setting value

Example: MSK 32

(All SRQs masked except error
SRQ.)

NR1 format:

3 digits
&bit status byte is sent as decimal charac­ter string (000 to 127)

Example: STS 122 (122=01111010)
NIX1 format:

2 digits
The latest error number is sent. If error
number is read after the error is cleared, 00
is sent.

Example: ERR 00 (Errors have been cleared.)
NRl format:

4 digits

Example: IDT 3940

Setting

Yes

Yes

No

No

No

4-34

SECTION 4

GPIB Inferface

4.4 TYPICAL EXECUTION TIMES

The execution times shown in Table 4-20 are the times re-

quired from the reception of the command execution is
complete. For inquiry messages, the execution time is the
time required from reception of the command to the time
when the output returns to the ready state. These execu­tion times are applicable only when a sweep is not in pro­gress. During a sweep, execution times may increase by a
factor of from two to one hundred, depending on the
sweep condition.

Table 4-20. Typical Execution Times

Function Header Time (ms) Message Time (ms)

Main Synthesizer

Oscillation Frequency
(Frequency:Hz)

Oscillation Frequency
(periods)

It takes about 05msec/byte for the Model 3940 to receive
a command from GPIB. The execution times given in the
table are those for which the number of message charac­ters is the same as the number of characters returned by
the corresponding inquiry.

It takes about 0.5msec/byte for the Model 3940 to transfer

data in the talker mode.

Setting Typical Typical

Message

J=Q

PRD

Execution Inquiry Execution

25 ?FRQ 15

25

?PRD 15

Output Amplitude
(VP-p/no load)

Output Amplitude
(VP-p/5OQ

Output Amplitude
(Vrms/no load)

Output Amplitude
(Vrms/5Osz>

Output Amplitude
(dBV/no load)

Outut Amplitude
(dBV/50SZ)

Output Amplitude
(dBm/50a)

DC Offset Voltage
(V/no load)

DC Offset Voltage

W/5OQ2)

15 ?AM.V

ATV 15

15

ATR

ATD

ATM

OFS

OFT

15

20 ?AMD

20

20

15

15

10

?ATV

10

?AMR 10

?ATR 10

10

?ATD 10

?ATM

?OFS

10

10

?OFT 10

Output Waveform
Oscillation Mode

FNC 10 ?FNC

10

MOD 10 ?MOD 10

4-35

SECTION 4

GPIB

Interface

Typical Execution Times (Cont.)

4-36

Typical Execution Times (Cont.)

SECTION 4

GPL!? Interface

Function

Main Synthesizer Sweep

Sweep Start Frequency

(Frequency:Hz)

Sweep Start Period

(Periods)

Sweep Stop Frequency

(Frequency:Hz)

Sweep Stop Period

(l?eriod:s)

Sweep Center Frequency

(Frequency:Hz)

Sweep Center Period

(Period:s)

Sweep Frequency Span

(Frequency:Hz)

Sweep Frequency Span

(Periods)

Setting

Message Execution

Header Time (ms)

STF 25

STD

SPF

SPD

CTF

CTD 25

SNF 25

SND 2-5

Typical

25

I

25

I

25

I

25

Typical

Inquiry

Message

?STF

?STD 15

?SPF

?SPD 15

?CTF 15

?CTD

Execution

Time (ms)

15

15

15

Sweep Marker Frequency

(Frequency:Hz)

Sweep Marker Frequency

(Period:s)

Marker Frequency +
Center Frequency

Sweep Time (s)
Sweep Function
Sweep Off
Continuous Sweep Start
Single Sweep Start
Sweep Start State
Sweep Stop State
Sweep Hold
Sweep Resume

MKF 25

25

--t
CFM 15

SCN 1 (Note)

z / ‘N”

+

2-i-e

RSM 1 15

--t

?MFD 15

?SFN j 10

-

-

- -

- -

- -

-

I -

I

I -

-

4-37

SECTION 4
GPIB Interface

Typical Execution Times (Cont.)

Setting Typical Typical

Message

Function Header Time (ms)

Execution

Inquiry

Message

Execution

Time (ms)

Main Synthesizer Sweep (Cont.)

Miscellaneous

SlNGL START IN con- SGE
nectar enable/disable in
remote mode

HOLD IN connector

HLE
enable/disable in remote
mode

Square wave duty cycle

DTY
(%I

Square wave duty cycle

50%

fixed

Inquiry on whether

DYF

-

square wave duty cycle is
variable or fixed at 50%

Main synthesizer output

CAL
amplitude calibration

Main synthesizer output

CAB
amplitude calibration

stop
Beep ON/OFF

BEE

15

?SGE

10

15 ?HLE 10

15

10

-

10

100

?DTY 10

-

?DYV

-

10

- -

-

-

10 ?BEE 10

4-38

Preset state

Function

Typical Execution Times (Cont.)

Inquiry

Message

SECTION 4

GPlB Interface

Typical

Execution

Time (ms)

mB Waveform Write and
Readout

33B

ARB waveform write and
readout format

ARB waveform write and
readout start address

Number of word for ARB
waveform write and
readout to be performed

ARB waveform readout
start

Number of words per
block for ASCII format
ARB waveform readout

ARB waveform readout
start

Response header
ON/OFF for inquiry
messages

SRQ mask
Status byte readout

WDN 20

SET 10

BLK

OUT 50

I

- -

15

?FMT

?STr

?WDN

?BLK

?HDR

?MSK

?STs

10

15

15

10

10

10

15
Error number readout
System Unit ID inquiry

NOlE When sweep calculation is performed, execution time varies considerably depending on sweep conditions. Maximum sweep calcula­tion time is about 1OOms.

- -

- -

?ERR

?IDT 10

10

4-39

SECTTON 4

GPIB

Interface

4.5 PROGRAM CODE SUMMARY TABLE

Table 4-21 shows the summary of the Model 3940 pro­gram codes.

Table 4-21. Program Codes Summary

Function

Main Synthesizer

Oscillation frequency
(Frequency:Hz)

Oscillation Frequency
(period:s)

Output Amplitude
(VP-p/no load)

Output Amplitude

wp-p/5w

Output Amplitude
(Vrms/no load)

In this table, the number of digits for response messages

are expressed in the form of (number of digits for man­tissa) + (number of digits for exponent). The number of
digits for the exponent is always 2.

Setting and

T

t

PRD NR3

Inquiry

Message

?FRQ

?PRD 6+2

NR3 ?A.MV 3+2

?ATV

?AMR

Number of

Digits for

Response*

12 + 2

3+2

3+2

Mantissa digits + exponent digits

Output Amplitude
(Vrms/5OQ)

Output Amplitude
(dBV/no load)

Output Amplitude
(dBV/50Q)

Output Amplitude
(dBm/50Q)

DC Offset Voltage
(V/no load)

DC Offset Voltage
07/5OQ2)

Output Waveform

0: c 1: 2/

%

:/I 5:l
6: ARB

Oscillation Mode
0: CONT 1: BRST
2: TRIG 3: GATE

3: /-L

ATR ?ATR

?ATD

?ATM

OFS ?OFS

FNC

MOD NRl ?MOD

NRl

?FNC 1

3+2

3+2

3+2

3+2

3+2

3+2

1

4-40

Function

SECTION4

GPIB Interface

Program Codes Summary (Cont.)

Output Amplitude

Main Synthesizer Trigger

Output Amplitude

SAD

(dBV/no load)

Output Waveform

lz2/ z

3:l-L
5:\

:

3y

Phase P: deg)
Trigger Source

SBF

SPH
TRS

0: EXTX 1: EXTB

2:INTl 3:INTJ

Panel key, function cor-

TRG
responding to MAN
0: Trigger inactive

1: Trigger active

Stop Level

SPL

0: HOLD

1: RESET
Mark Wave Cycles
Space Wave CycIes SIT

NR2 ?SAD

NRl ?SBF

NR2

15

?SPH

?TRS

NRl ?TRG

NRl

?SPL

NR2 ?MRK
NR2 ?Sl?C

3

1

4

1

1

1

6
6

*Mantissa digits + exponent digits

Phase (“: deg)
Phase Sync
EXT TRIG IN connector

enable/disable in remote
mode
0: Disable
1: Enable

PHS NR2
SYN

- -

NRl

?PHS

4

-

?TRE 1

4-41

SECTION 4

GPIB Interface

Program Codes Summary (Cont.)

Main Synthesizer Sweep

Function

Sweep Start Frequency
(Frequency:Hz)

Sweep Start Period
(Period:s)

Sweep Stop Frequency

(Frequency: Hz)

Sweep Stop Period

(Period:s)

Sweep Center Frequency

(Frequency: I-TZ)

Sweep Center Period
(Period:s)

Sweep Frequency Span
(Frequency: Hz)

Sweep Frequency Span
(Period: s)

Setting and

Response Messages Inquiry Digits for

Header

Parameter

Message

STF NR3 ?STF

STD NR3 ?STD

SPF NR3 ?SPF

SPD NR3 ?SPD

CTF

CTD

NR3

NR3

?CTF 12+2

?CTD 6+2

SNF NR3 ?SNF

SND

NR3 ?SND

Number of

Response

12+2

6+2

12+2

6+2

12+2

6+2

Sweep Marker Frequency

MKF

(Frequency: Hz)
Sweep Marker Period

MKD NR3 ?MFD

(Period: s)
Marker frequency sub-

stitute to center frequency
Sweep Time (s)
Sweep Function

STM NR3 ?STM 4-1-2

SFN
o:J- 1: LINA
2: LIN// 3: LOG A

4: LOG/l
Sweep Off- ~~

SOF

Continuous Sweep Start SCN
Single Sweep Start
Sweep Start State
Sweep Stop State
Sweep Hold

SSG

SST
SSP

HLD

NR3 ?MKF

12+2

6+2

- - -

NRl ?SFN 1

- -

-

-

-

- -

- -

- -

-

- - -

-

-

-

442