Lecroy lc revp schematic

Remote Control
Manual

LeCroy
9300 & LC
Oscilloscopes

Revision P

LeCroy Corporation

700 Chestnut Ridge Road
Chestnut Ridge, NY 10977–6499
Tel: [phone], Fax: [phone]

Internet: www.lecroy.com

© 2001 by LeCroy Corporation. All rights reserved. Information in this publication supersedes all earlier versions. Specifications subject to
change.

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Chapter 1 — Overview of Remote C ontrol

Chapter 1 — Overview of Remote C ontrol

Chapter 1 — Overview of Remote C ontrolChapter 1 — Overview of Remote C ontrol

How to Operate the Oscilloscope Remotely

How to Operate the Oscilloscope Remotely............................1–1

How to Operate the Oscilloscope RemotelyHow to Operate the Oscilloscope Remotely

Chapter 2 — GPIB

Chapter 2 — GPIB

Chapter 2 — GPIBChapter 2 — GPIB

Communication via the GPIB Bus

Communication via the GPIB Bus..................................................2–1

Communication via the GPIB BusCommunication via the GPIB Bus
Instrument Polls

Instrument Polls ..................................................................................2–13

Instrument PollsInstrument Polls
Driving Hardcopy Devices on the GPIB

Driving Hardcopy Devices on the GPIB.....................................2–19

Driving Hardcopy Devices on the GPIBDriving Hardcopy Devices on the GPIB
Printing by GPIB Controller

Printing by GPIB Controller.............................................................2–20

Printing by GPIB ControllerPrinting by GPIB Controller

Chapter 3 — RS-232-C

Chapter 3 — RS-232-C

Chapter 3 — RS-232-CChapter 3 — RS-232-C

Using the RS-232-C Port

Using the RS-232-C Port.....................................................................3–1

Using the RS-232-C PortUsing the RS-232-C Port
Simulating GPIB Commands with RS-232-C

Simulating GPIB Commands with RS-232-C.............................3–6

Simulating GPIB Commands with RS-232-CSimulating GPIB Commands with RS-232-C

Chapter 4 — Waveform

Chapter 4 — Waveform

Chapter 4 — WaveformChapter 4 — Waveform

Understanding Waveforms

Understanding Waveforms................................................................4–1

Understanding WaveformsUnderstanding Waveforms
Using the INSPECT? Query

Using the INSPECT? Query...............................................................4–4

Using the INSPECT? QueryUsing the INSPECT? Query
WAVEFORM?, Related Commands, and Blocks

WAVEFORM?, Related Commands, and Blocks......................4–6

WAVEFORM?, Related Commands, and BlocksWAVEFORM?, Related Commands, and Blocks
High-Speed Waveform Transfer

High-Speed Waveform Transfer....................................................4–15

High-Speed Waveform TransferHigh-Speed Waveform Transfer

Contents

Contents

ContentsContents

Chapter 5 — Status Regis ters

Chapter 5 — Status Regis ters

Chapter 5 — Status Regis tersChapter 5 — Status Regis ters

Using Status Registers

Using Status Registers.......................................................................5–1

Using Status RegistersUsing Status Registers

SYSTEM COMMANDS

SYSTEM COMMANDS

SYSTEM COMMANDSSYSTEM COMMANDS

About These Commands & Queries

About These Commands & Queries.....................................................1

About These Commands & QueriesAbout These Commands & Queries
… Tabled By Long Form

… Tabled By Long Form .........................................................................3

… Tabled By Long Form… Tabled By Long Form
… Tabled By Subsystem

… Tabled By Subsystem ........................................................................8

… Tabled By Subsystem… Tabled By Subsystem

The Commands and Queries

The Commands and Queries..............................................................12

The Commands and QueriesThe Commands and Queries

Appendix A — GPIB Program Examples

Appendix A — GPIB Program Examples

Appendix A — GPIB Program ExamplesAppendix A — GPIB Program Examples
Appendix B — Waveform Template

Appendix B — Waveform Template

Appendix B — Waveform TemplateAppendix B — Waveform Template
Index

Index

IndexIndex

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Overview of Remote Control

Overview of Remote Control

1111

How to Operate the Oscilloscope Remotely

How to Operate the Oscilloscope Remotely

How to Operate the Oscilloscope RemotelyHow to Operate the Oscilloscope Remotely

Your LeCroy oscilloscope can of course be operated

manually, using the front-panel controls (see the
accompanying Operator’s Manual ). But it can also be

operated remotely by means of an external controller.
Normally, this controller will be a computer. However, it may
beasimpleterminal.

The present manual describes how to remotely control the
oscilloscope. Its main section provides the system commands for
executing the instrument’s functions from an external controller.

Remote control is done using either the GPIB (General Purpose
Interface Bus) — labeled “IEEE Std 488-2” — or the RS-232-C
communication port on the rear panel of the oscilloscope. The
instrument can be fully controlled in remote mode, the only
actions not able to be performed being the powering-on of the
oscilloscope and the setting of remote addresses.

Illustrated above and
below-right, the GPIB
(IEEE Std 488-2)and
RS-232-C ports found on
the back of LeCroy
oscilloscopes, used for
connecting the instrument
to an external controller.
They are vertically or
horizontally arranged on
the back panel according
to model.

In this chapter, the basic remote control concepts common to
both GPIB and RS-232-C are introduced. Also presented is a
brief description of the remote control messages. The following
two chapters set out how to send program messages over the
GPIB and RS-232-C interfaces, respectively. Chapter 4 offers a
detailed description and run-through of the transfer and
formatting of waveforms. While Chapter 5 explains the use of
status bytes for error reporting.

The special System Commands section provides a complete
directory and description of the system commands. And the
Appendices offer GPIB Program Examples (Appendix A) and a
Waveform Template (Appendix B).

Overview of Remote ControlOverview of Remote Control

GPIB Standard

GPIB Standard The remote com mands

GPIB StandardGPIB Standard

conform to the
GPIB IEEE

*

488.2
which may be

* ANSI/IEEE Std. 488.2–1987, IEEE Standard Codes, Formats, Protocols, and Common

Commands. The Institute of Electrical and Electronics Engineers Inc., 345 East 47th Street,

New York, NY 10017, USA.

LCXXX-RM-E Rev P ISSUED: September 2001 1–1

standard,

About Remote Control

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About Remote ControlAbout Remote Control

considered as an extension of the IEEE 488.1 standard, dealing
mainly with electrical and mechanical issues. The IEEE 488.2
recommendations have also been adopted for RS-232-C
communications wherever applicable.

Program Messages

Program Messages To control the oscilloscope remotely, the program messages

Program MessagesProgram Messages

sent from the external controller must conform to precise format
structures. The oscilloscope will execute all program messages
sent in the correct form, but will ignore those where errors are
detected.

Warning or error messages are normally not reported unless the
controller explicitly examines the relevant status register. Or if the
status-enable registers have been set so that the controller can
be interrupted when an error occurs.

During the development of the control program it is possible to
observe all remote control transactions, including error
messages, on an external monitor connected to the RS-232-C
port. Refer to the command “COMM_HELP” for further details.

Commands and Queries

Commands and Queries Program messages consist of either one or several commands

Commands and QueriesCommands and Queries

or queries.
Whereas the command directs the instrument to change its state —

its timebase or vertical sensitivity, for example — the query asks the
instrument about that state. Very often, the same mnemonic is used
for a command and a query, the query being identified by a <?> after
the last character.

For example, to change the timebase to 2 ms/div, the controller
sends the following command to the instrument:

TIME_DIV 2 MS

To ask the instrument about its timebase, this query should be
sent:

TIME_DIV?

A query causes the instrument to send a response message.
The control program should read this message with a ‘read’
instruction to the GPIB or RS-232-C interface of the controller.
The response message to the query above might be:

TIME_DIV 10 NS

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The portion of the query preceding the question mark is repeated
as part of the response message. If desired, this text may be
suppressed with the command “COMM_HEADER”.

Depending on the state of the instrument and the computation to
be done, up to several seconds may pass before a response is
received. Command interpretation does not have priority over
other oscilloscope activities. It is therefore judicious to set the
controller IO timeout conditions to three or more seconds. In
addition, it should always be remembered that an incorrect query
message will not generate a response message.

Program Message Form

Program Message Form An instrument is remotely controlled with program messages that

Program Message FormP rogram Mes sage For m

consist of one or several commands or queries, separated by
semicolons <;> and ending in a terminator:

<command/query>;.........;<command/query>

<terminator>

Upper or lower-case characters or both can be used in program
messages.

The instrument does not decode incoming program messages
before receiving a terminator. The exception to this is when the
program message is longer than the 256 byte input buffer: the
oscilloscope will start analyzing the message when the buffer is
full. Commands and queries are executed in the order in which
they are transmitted.

In GPIB mode, the following are valid terminators:

<NL> New-line character (i.e. the ASCII new-

line character, whose decimal value is

10).

<NL> <EOI> New-line character with a simultaneous

<EOI> signal.

<EOI> <EOI> signal together with the last

character of the program message.

Note:

Note: The <EOI> signal is a dedicated GPIB interface line

Note:Note:

which can be set with a special call to the GPIB interface
driver. Refer to the GPIB interface manufacturer’s manual
and support programs.

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The <NL> <EOI> terminator is always used in response
messages sent by the instrument to the controller.

In RS-232-C, the terminator may be defined by the user with the
command “COMM_RS232”. The default value is <CR>, i.e. the
ASCII carriage return character, the decimal value of which is 13.

Examples

Examples GRID DUAL

ExamplesExamples

This program message consists of a single command that
instructs the instrument to display a dual grid. The terminator is
not shown, as it is usually automatically added by the interface
driver routine writing to the GPIB (or RS-232).

DZOM ON; DISPLAY OFF; DATE?

This program message consists of two commands, followed by a
query. They instruct the instrument to turn on the multi-zoom
mode, turn off the display, and then ask for the current date.
Again, the terminator is not shown.

Command/Query Form

Command/Query Form The general form of a command or a query consists of a

Command/Query FormCommand/Query Form

command header <header> optionally followed by one or several
parameters <data> separated by commas:

<header>[?] <data>,...,<data>

The notation [?] shows that the question mark is optional (turning
the command into a query). The detailed listing of all commands
in System Commands indicates which may also be queries.
There is a space between the header and the first parameter.
There are commas between parameters.

Example

Example DATE 15,JAN,1993,13,21,16

ExampleExample

This command instructs the oscilloscope to set its date and time
to 15 JAN 1993, 13:21:16. The command header “DATE”
indicates the action, the 6 data values specify it in detail.

Header

Header The header is the mnemonic form of the operation to be

HeaderHeader

performed by the oscilloscope. All command mnemonics are
listed in alphabetic order in the System Commands section.

The majority of the command/query headers have a long form for
optimum legibility and a short form for better transfer and
decoding speed. The two forms are fully equivalent and can be

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used interchangeably. For example, the following two commands
for switching to the automatic trigger mode are fully equivalent:

TRIG_MODE AUTO and TRMD AUTO

Some command/query mnemonics are imposed by the IEEE

488.2 standard. They are standardized so that different
instruments present the same programming interface for similar
functions. All these mnemonics begin with an asterisk <*>. For
example, the command “*RST” is the IEEE 488.2 imposed
mnemonic for resetting the instrument, whereas “*TST?”
instructs the instrument to perform an internal self-test and to
report the outcome.

Header path

Header path Some commands or queries apply to a sub-section of the

Header pathHeader path

oscilloscope — for example, a single input channel or a trace on
the display. In such cases, the header must be preceded by a
path name that indicates the channel or trace to which the
command applies. The header path normally consists of a two­letter path name followed by a colon <:> immediately preceding
the command header.

One of the waveform traces can usually be specified in the
header path (refer to the individual commands listed in System
Commands for details of the values applying to given command
headers):

C1, C2 Channels 1 and 2
C3, C4 Channels 3 and 4
M1, M2, M3, M4 Memories 1, 2, 3, 4
TA, TB, TC, TD Traces A, B, C and D
EX, EX10, EX5 External trigger
LINE LINE source for trigger

†

Example

Example C1:OFST -300 MV

ExampleExample

Commands to set the offset of Channel 1 to −300 mV.
Header paths need only be specified once. Subsequent

commands with header destinations not indicated are assumed
to refer to the last defined path. For example, the following
commands are identical:

†

On four-channel instruments only.

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C2:VDIV?; C2:OFST? What is the vertical sensitivity

and the offset of channel 2?

C2:VDIV?; OFST? Same as above, without

repeating the path.

Data

Data Whenever a command/query uses additional data values, the

DataData

values are expressed in terms of ASCII characters. There is a
single exception: the transfer of waveforms with the
command/query “WAVEFORM”, where the waveform may be
expressed as a sequence of binary data values. Chapter 4 gives

a detailed explanation of waveform format.

ASCII data can have the form of character, numeric, string or
block data.

Character data

Character data These are simple words or abbreviations for the indication of a

Character dataCharacter data

specific action.

Example

Example DUAL_ZOOM ON

ExampleExample

Here, the data value “ON” commands that the dual-zoom mode
be turned on (the data value “OFF” in such a case will obviously
have the opposite effect).

However, this can become more complex. In some commands,
where as many as a dozen different parameters are able to be
specified, or where not all the parameters are applicable at the
same time, the format requires pairs of data values. The first
value names the parameter to be modified, while the second
gives its value. Only those parameter pairs changed need
indicating:

Example

Example HARDCOPY_SETUP DEV,EPSON,PORT,GPIB

ExampleExample

Here, two pairs of parameters are specified. The first specifies
the device as the EPSON printer (or compatible) and the second
indicates the GPIB port. While the command
“HARDCOPY_SETUP” allows many more parameters, they are
either not relevant for printers or are left unchanged.

Numeric Data

Numeric Data The numeric data type is used to enter quantitative information.

Numeric DataNumeric Data

Numbers can be entered as integers or fractions, or in
exponential representation:

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TA:VPOS -5 Move the displayed trace of

Trace A downwards by five
divisions.

C2:OFST 3.56 Set the DC offset of Channel 2

to 3.56 V.

TDIV 5.0E-6 Adjust the timebase to 5 µs/div.

Note:

Note: Numeric values may be followed by multipliers and

Note:Note:

units, modifying the value of the numerical expression.
The following mnemonics are recognized:

EX 1E18 Exa- PE 1E15 Peta­T 1E12 Tera- G 1E9 Giga­MA 1E6 Mega- K 1E3 kilo­M

N

F

Examples

Examples There are many ways of setting the timebase of the instrument to

ExamplesExamples

1E−−−−3
1E−−−−9

1E−−−−15

milli- U

nano- PI

femto- A

1E−−−−6
1E−−−−12
1E−−−−18

micro-

pico-

atto-

5µs/div:

TDIV 5E-6 Exponential notation, without any suffix.
TDIV 5 US Suffix m ultiplier “U” for 1E−6, with the

(optional) suffix “S” for seconds.

or

TDIV 5000 NS
TDIV 5000E-3 US

String Data

String Data This data type enables the transfer of a (long) string of

String DataString Data

characters as a single parameter. String data are formed by
simply enclosing any sequence of ASCII characters between
single or double quotation marks:

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MESSAGE ‘Connect probe to point J3’

The instrument displays this message in the Message field above
the grid.

Block Data

Block Data These are binary data values coded in hexadecimal ASCII, i.e.

Block DataBlock Data

4-bit nibbles translated into the digits 0,...9, A,...F and transmitted
as ASCII characters. They are used only for the transfer of
waveforms (Command “WAVEFORM”) and of the instrument
configuration (Command “PANEL_SETUP”)

Response Message Form

Response Message Form The instrument sends a response message to the controller, as

Response Message FormResponse Message Form

an answer to a query. The format of such messages is the same
as that of program messages, i.e. individual responses in the
format of commands, separated by semicolons <;> and ending
with a terminator. They can be sent back to the instrument in the
form in which they are received, to be accepted as valid
commands. In GPIB response messages, the <NL> <EOI>
terminator is always used.

For instance, if the controller sends the program message:

TIME_DIV?;TRIG_MODE NORM;C1:COUPLING?

(terminator not shown).

The instrument might respond as follows:

TIME_DIV 50 NS;C1:COUPLING D50 (terminator not
shown).

The response message refers only to the queries:
“TRIG_MODE” is left out. If this response is sent back to the
instrument, it is a valid program message for setting its timebase
to 50 ns/div and the input coupling of Channel 1 to 50 W.

Whenever a response is expected from the instrument, the
control program must instruct the GPIB or RS-232-C interface to
read from the instrument. If the controller sends another program
message without reading the response to the previous one, the
response message in the output buffer of the instrument is
discarded.

The instrument uses somewhat stricter rules for response
messages than for the acceptance of program messages.
Whereas the controller may send program messages in upper or
lower case characters, response messages are always returned

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in upper case. Program messages may contain extraneous
spaces or tabs (white space): response messages will not. And
while program messages may contain a mixture of short and
long command/query headers, response messages always use
short headers by default.

However, the instrument can be forced, using the command
“COMM_HEADER”, to use long headers, or no headers at all. If
the response header is omitted, the response transfer time is
minimized, but such a response will not be able to be sent back
to the instrument. Suffix units are also suppressed in the
response.

If the trigger slope of Channel 1 is set to negative, the query
“C1:TRSL?” might yield the following responses:

C1:TRIG_SLOPE NEG header format: long
C1:TRSL NEG header format: short
NEG header format: off

Waveforms which are obtained from the instrument using the
query “WAVEFORM?” constitute a special kind of response
message. Their exact format can be controlled via the
“COMM_FORMAT” and “COMM_ORDER” commands.

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GPIB

GPIB

2222

Communication via the GPIB Bus

Communication via the GPIB Bus

Communication via the GPIB BusCommunication via the GPIB Bus

This chapter describes how to remotely control the
oscilloscope using the General Purpose Interface Bus
(GPIB). Discussed are interface capabilities, addressing,
standard bus commands, and polling schemes. See also the

“Utilities” chapter in the accompanying Operator’s Manual
and “Hands-On Guide”.

GPIB Structure

GPIB Structure GPIB is similar to a standard computer bus. But whereas a

GPIB StructureGPIB Structure

computer interconnects circuit cards via a backplane bus, the
GPIB interconnects independent devices by means of a cable
bus. GPIB also carries both program and interface messages.

Program messages, often called device-dependent
messages, contain programming instructions, measurement
results, instrument status and waveform data. Their general

form is described in the previous chapter.

Interface messages manage the bus itself. They perform
functions such as its initialization, the addressing and
“unaddressing” of devices, and the setting of remote and
local modes.

GPIBGPIB

Talkers and Listeners

Talkers and Listeners Devices connected by GPIB can be listeners, talkers, or

Talkers and ListenersT alker s and Li st eners

controllers. A talker sends program messages to one or more
listeners, while the controller manages the flow of information on
the bus by sending interface messages to the devices.

The oscilloscope can be a talker or listener, but not a controller.
The host computer must be able to play all three roles.

Interface Capabilities

Interface Capabilities The interface capabilities of the oscilloscope include the following

Interface CapabilitiesInterface C apabilities

IEEE 488.1 definitions:

*

For details of how the controller configures the GPIB for specific functions, refer to the GPIB

interface manufacturer’s manual.

LCXXX-RM-E Rev P ISSUED: September 2001 2–1

*

GPIB

GPIB

GPIBGPIB

AH1 Complete Acceptor Hands hake
SH1 Complete Source Handshake
L4 Partial Listener Function
T5 Complete Talker Function
SR1 Complete Service Request Func tion
RL1 Complete Remote/Local F unction
DC1 Complete Device Clear Function
DT1 Com plete Device Trigger
PP1 Parallel Polling: rem ote configurability
C0 No Controller Functions
E2 Tri-state Drivers

Addressing

Addressing Every device on the GPIB has an address. When the remote

AddressingAddressing

control port is set to “GPIB”, using the oscilloscope’s front-panel­operated “UTILITIES” menus, the instrument can be controlled
via GPIB. When the remote control port is set to “RS-232” by the
same means, the instrument will execute solely “talk-only”
operations over the GPIB, such as driving a printer. Setting the
oscilloscope to “RS-232” enables the instrument to be controlled
via the RS-232-C port (see next chapter).

If the oscilloscope is addressed to talk, it will remain thus
configured until receiving a universal untalk command (UNT), its
own listen address (MLA), or another instrument’s talk address.

Similarly, if the oscilloscope is addressed to listen, it will remain
configured to listen until a universal unlisten command (UNL), or
its own talker address (MTA), is received.

GPIB Signals

GPIB Signals The bus system consists of 16 signal lines and eight ground or

GPIB SignalsGPIB Signals

shield lines. The signal lines are divided into three groups:

1. Data Lines: These eight lines, usually called DI01 through to
DI08, carry both program and interface messages. Most of
the messages use the 7-bit ASCII code, in which case DI08
is unused.

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2. Handshake Lines: These three lines control the transfer of
message bytes between devices. The process is called a
three-wire interlocked handshake and it guarantees that the
message bytes on the data lines are sent and received
without transmission error.

3. Interface Management Lines: These five lines manage the
flow of information across the interface:

ATN (ATteNtion): The controller drives the ATN line true
when it uses the data lines to send interface messages
such as talk and listen addresses or a device clear (DCL)
message. When ATN is false, the bus is in data mode
for the transfer of program messages from talkers to
listeners.

IFC (InterFace Clear): The controller sets the IFC line
true to initialize the bus.

REN (Remote ENable): The controller uses this line to
place devices in remote or local program mode.

SRQ (Service ReQuest): Any device can drive the SRQ
line true to asynchronously request service from the
controller. This is the equivalent of a single interrupt line
on a computer bus.

EOI (End Or Identify): This line has two purposes. The
talker uses it to mark the end of a message string. The
controller uses it to tell devices to identify their response
in a parallel poll (discussed later in this section).

I/O Buffers

I/O Buffers The instrument has 256-byte input and output buffers. An

I/O BuffersI/O Buffers

incoming program message is not decoded before a message
terminator has been received. However, if the input buffer
becomes full (because the program message is longer than the
buffer), the instrument starts analyzing the message. In this case
data transmission is temporarily halted, and the controller may
generate a timeout if the limit was set too low.

IEEE 488.1 Standard

IEEE 488.1 Standard

IEEE 488.1 StandardIEEE 488.1 Standard
Messages

Messages

MessagesMessages

LCXXX-RM-E Rev P ISSUED: September 2001 2–3

The IEEE 488.1 standard specifies not only the mechanical and
electrical aspects of the GPIB, but also the low-level transfer
protocol — for instance, it defines how a controller addresses
devices, turns them into talkers or listeners, resets them or puts

GPIB

GPIB

GPIBGPIB

Note:

Note: In addition to the IEEE 488.1 interface message

Note: Note:

standards, the IEEE 488.2 standard specifies certain
standardized program messages, i.e. command headers.
They are identified with a leading asterisk <*> and are listed in
the System Commands section.

them in the remote state. Such interface messages are executed
with the interface management lines of the GPIB, usually with
ATN true.

All of these messages (except GET) are executed immediately
upon reception and not, with normal commands, in chronological
order.

The command list in System Commands does not contain a
command for clearing the input or output buffers, nor for setting
the instrument to the remote state. This is because such
commands are already specified as IEEE 488.1 standard
messages. Refer to the GPIB interface manual of the host

controller as well as to its support programs, which should
contain special calls for the execution of these messages.

The following description covers those IEEE 488.1 standard
messages which go beyond mere reconfiguration of the bus and
have an effect on the operation of the instrument.

Device CLear

Device CLear In response to a universal Device CLear (DCL) or a Selected

Device CLearDevice CLear

Device Clear message (SDC), the oscilloscope clears the input
or output buffers, aborts the interpretation of the current
command (if any) and clears pending commands. However,
status registers and status-enable registers are not cleared.
Although DCL has an immediate effect it can take several
seconds to execute if the instrument is busy.

Group Execute Trigger

Group Execute Trigger The Group Execute Trigger message (GET) causes the

Group Execute TriggerGroup Execute Trigger

oscilloscope to arm the trigger system. It is functionally identical
to the “*TRG” command.

Remote ENable

Remote ENable This interface message is executed when the controller holds the

Remote ENableRemote ENable

Remote ENable control line (REN) true and configures the
instrument as a listener. All the front-panel controls except the
menu buttons are disabled. The menu indications on the right­hand side of the screen no longer appear, since menus cannot

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now be operated manually. Instead, the text REMOTE ENABLE
appears at the top of the menu field to indicate that the
instrument is set to the remote mode. Whenever the controller
returns the REN line to false, all instruments on the bus return to
GO TO LOCAL. Individual instruments can be returned to
LOCAL with the Go To Local message (see below).

Local front-panel control may be regained by pressing the GO
TO LOCAL menu button, unless the instrument has been placed
in Local LOckout (LLO) mode.

Local LOckout

Local LOckout The Local LOckout command (LLO) causes the GO TO LOCAL

Local LOckoutLocal LOckout

menu to disappear. The LLO command can be sent in local or
remote mode but only becomes effective once the instrument
has been set to the remote mode.

Go To Local

Go To Local The Go To Local message (GTL) causes the instrument to return

Go To LocalGo To Local

to local mode. All front-panel controls become active and the
normal menus reappear. Thereafter, whenever the instrument is
addressed as a listener it will be immediately reset to the remote
state — except when the LLO command has been sent.

When Local Lockout is activated the scope can only be returned
to its local state by the controller returning the LLO to false. And
whenever the instrument returns to the remote state the local
lockout mode will immediately become effective again.

InterFace Clear

InterFace Clear The InterFace Clear message (IFC) initializes the GPIB but has

InterFace ClearInterFace Clear

no effect on the operation of the oscilloscope.

Programming GPIB

Programming GPIB

Programming GPIBProgramming GPIB
Transfers

Transfers

TransfersTransfers

LCXXX-RM-E Rev P ISSUED: September 2001 2–5

To illustrate the GPIB programming concepts a number of examples
written in BASICA are included here. It is assumed that the controller

is IBM-PC compatible, running under DOS, and that it is equipped
with a National Instruments
GPIB programming with other languages such as C or Pascal is
quite similar to this.

If using another type of computer or GPIB interface, refer to the
interface manual for installation procedures and subroutine calls.

†

National Instruments Corporation, 12109 Technology Boulevard, Austin, Texas 78727, USA.

†

GPIB interface card. Nevertheless,

Configuring the

Configuring the

Configuring theConfi guring t he
GPIB Driver Hardware

GPIB Driver Hardware

GPIB Driver HardwareGPIB Driver Hardware

Configuring the

Configuring the

Configuring theConfi guring t he
GPIB Driver Software

GPIB Driver Software

GPIB Driver SoftwareGPIB Driver Software

GPIB

GPIB

GPIBGPIB

Check that the GPIB interface is properly installed in the
computer. If found that it is not, follow the interface
manufacturer’s installation instructions. In the case of the
National Instruments interface, it is possible to modify the base
I/O address of the board, the DMA channel number and the
interrupt line setting using switches and jumpers.

In these program examples, default positions are assumed.
Connect the oscilloscope to the computer with a GPIB interface

cable. Set the GPIB address to the required value. The program
examples assume a setting of ‘4’.

The host computer requires an interface driver that handles the
transactions between the operator’s programs and the interface
board. In the case of the National Instruments interface, the
installation procedure copies the GPIB handler GPIB.COM into the
boot directory, modifies the DOS system configuration file
CONFIG.SYS to declare the presence of the GPIB handler,
creates a sub-directory GPIB-PC, and installs in GPIB-PC a
number of files and programs useful for testing and reconfiguring
the system and for writing user programs.

The following files in the sub-directory GPIB-PC are particularly
useful:

IBIC.EXE allows interactive control of the GPIB via functions
entered at the keyboard. Use of this program is highly
recommended to anyone unfamiliar with GPIB programming
or the oscilloscope’s remote commands.

DECL.BAS is a declaration file that contains code to be
included at the beginning of any BASICA application
program. Simple application programs can be quickly written
by appending the operator’s instructions to DECL.BAS and
executing the complete file.

IBCONF.EXE is an interactive program that allows inspection
or modification of the current settings of the GPIB handler.

To run IBCONF.EXE, refer to the National Instruments
manual.

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In the program examples in this section, it is assumed that the
National Instruments GPIB driver GPIB.COM is in its default
state — i.e. that the user has not modified it with IBCONF.EXE.
This means that the interface board can be referred to by the
symbolic name ‘GPIB0’ and that devices on the GPIB bus with
addresses between 1 and 16 can be called by the symbolic
names ‘DEV1’ to ‘DEV16’.

Note

Note:

Note:Note

In the program examples in this section, it is assumed
that the National Instruments GPIB driver GPIB.COM is
in its default state — i.e. that the user has not modified
it with IBCONF.EXE. This means that the interface
board can be referred to by the symbolic name ‘GPIB0’
and that devices on the GPIB bus with addresses
between 1 and 16 can be called by the symbolic names
‘DEV1’ to ‘DEV16’.

If you have a National Instruments PC2 interface card
rather than PC2A, you must run IBCONF to declare the
presence of this card rather than the default PC2A.

Simple Transfers

Simple Transfers For a large number of remote control operations it is sufficient to

Simple TransfersSimple Transfers

use just three different subroutines (IBFIND, IBRD and IBWRT)
provided by National Instruments. The following complete
program reads the timebase setting of the oscilloscope and
displays it on the terminal:

1–99 <DECL.BAS>
100 DEV$=“DEV4”
110 CALL IBFIND(DEV$,SCOPE%)
120 CMD$=“TDIV?”
130 CALL IBWRT(SCOPE%,CMD$)
140 CALL IBRD(SCOPE%,RD$)
150 PRINT RD$
160 END

Lines 1–99 are a copy of the file DECL.BAS supplied by National
Instruments. The first six lines are required for the initialization of
the GPIB handler. The other lines are declarations which may be
useful for larger programs, but are not really required code. The

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GPIB

GPIB

GPIBGPIB

sample program above only uses the strings CMD$ and RD$
which are declared in DECL.BAS as arrays of 255 characters.

Note:

Note:

Note:Note:

DECL.BAS requires access to the file BIB.M during the
GPIB initialization. BIB.M is one of the files supplied by
National Instruments, and it must exist in the directory
currently in use.

The first two lines of DECL.BAS both contain a string
“XXXXX” which must be replaced by the number of
bytes which determine the maximum workspace for
BASICA (computed by subtracting the size of BIB.M
from the space currently available in BASICA). For
example, if the size of BIB.M is 1200 bytes and when
BASICA is loaded it reports “60200 bytes free”, you
should replace “XXXXX” by the value 59 000 or less.

Lines 100 and 110 open the device “DEV4” and associate with it
the descriptor “SCOPE%”. All I/O calls after that will refer to
“SCOPE%”. The default configuration of the GPIB handler
recognizes “DEV4” and associates with it a device with GPIB
address 4.

Lines 120 and 130 prepare the command string TDIV? and
transfer it to the instrument. The command instructs the
instrument to respond with the current setting of the timebase.

Lines 140 and 150 reads the response of the instrument and
places it into the character string RD$.

Line 170 displays the response on the terminal.
When running this sample program, the oscilloscope will

automatically be set to the remote state when IBWRT is
executed, and will remain in that state. Pressing the LOCAL
menu button will return the oscilloscope to local mode if the GPIB
handler was modified to inhibit Local LOckout (LLO).

Here is a slightly modified version of the sample program which
checks if any error occurred during GPIB operation:

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1–99 <DECL.BAS>
100 DEV$=“DEV4”
110 CALL IBFIND(DEV$,SCOPE%)
120 CMD$=“TDIV?”
130 CALL IBWRT(SCOPE%,CMD$)
140 IF ISTA% < 0 THEN GOTO 200
150 CALL IBRD(SCOPE%,RD$)
160 IF ISTA% < 0 THEN GOTO 250
170 PRINT RD$
180 IBLOC(SCOPE%)
190 END
200 PRINT “WRITE ERROR =”;IBERR%
210 END
250 PRINT “READ ERROR =”;IBERR%
260 END

The GPIB status word ISTA%, the GPIB error variable IBERR%
and the count variable IBCNT% are defined by the GPIB handler
and are updated with every GPIB function call. Refer to the
National Instruments manual for details. The sample program
above would report if the GPIB address of the instrument was set
to a value other then 4. Line 180 resets the instrument to local
with a call to the GPIB routine IBLOC.

Additional Driv er C al ls

Additional Driv er C al ls IBLOC is used to execute the IEEE 488.1 standard message Go

Additional Driv er C al lsAdditional Driv er C al ls

To Local (GTL), i.e. it returns the instrument to the local state.
The programming example above illustrates its use.

IBCLR executes the IEEE 488.1 standard message Selected
Device Clear (SDC).

IBRDF and IBWRTF, respectively, allow data to be read from
GPIB to a file, and written from a file to GPIB. Transferring data
directly to or from a storage device does not limit the size of the
data block, but may be slower than transferring to the computer
memory.

IBRDI and IBWRTI, respectively, allow data to be read from
GPIB to an integer array, and written from integer array to GPIB.
Since the integer array allows storage of up to 64 kilobytes (in
BASIC), IBRDI and IBWRTI should be used for the transfer of
large data blocks to the computer memory, rather than IBRD or

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GPIB

GPIB

GPIBGPIB

IBWRT, which are limited to 256 bytes by the BASIC string
length. Note that IBRDI and IBWRTI only exist for BASIC, since
for more modern programming languages, such as C, the
function calls IBRD and IBWRT are far less limited in terms of
data-block size.

IBTMO can be used to change the timeout value during program
execution. The default value of the GPIB driver is 10 seconds —
for example, if the instrument does not respond to an IBRD call,
IBRD will return with an error after the specified time.

IBTRG executes the IEEE 488.1 standard message Group
Execute Trigger (GET), which causes the oscilloscope to arm the
trigger system.

National Instruments supply a number of additional function calls.
In particular, it is possible to use the so-called board level calls
which allow a very detailed control of the GPIB.

Service Requests

Service Requests When an oscilloscope is used in a remote application, events

Service RequestsService Requests

often occur asynchronously — at times that are unpredictable for
the host computer. The most common example of this is the wait
of a trigger after the arming of the instrument: the controller must
wait until the acquisition is finished before it can read the
acquired waveform. The simplest way of checking if a certain
event has occurred is by either continuously or periodically
reading the status bit associated with it until the required
transition is detected. Continuous status bit polling is described in

more detail below. For a complete explanation of status bytes
refer to Chapter 5.

A potentially more efficient way of detecting events occurring in
the instrument is the use of the Service Request (SRQ). This
GPIB interrupt line can be used to interrupt program execution in
the controller. The controller can then execute other programs
while waiting for the instrument. Unfortunately, not all interface
manufacturers support the programming of interrupt service
routines. In particular, National Instruments supports only the
SRQ bit within the ISTA% status word. This requires the user to
continuously or periodically check this word, either explicitly or
with the function call IBWAIT. In the absence of real interrupt
service routines the use of SRQ may not be very advantageous.

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In the default state, after power-on, the Service ReQuest is
disabled. The SRQ is enabled by setting the Service Request
Enable register with the command “*SRE” and specifying which
event should generate an SRQ. The oscilloscope will interrupt
the controller as soon as the selected event(s) occur by asserting
the SRQ interface line. If several devices are connected to the
GPIB, the controller may be required to identify which instrument
caused the interrupt by serial polling the various devices.

Note:

Note: The SRQ bit is latched until the controller reads the

Note:Note:

STatus Byte Register (STB). The action of reading the STB
with the command “*STB?” clears the register contents except
the MAV bit (bit 4) until a new event occurs. Service requesting
may be disabled by clearing the SRE register (“*SRE 0”).

Example 1

Example 1 To assert SRQ in response to the events “new signal

Example 1Example 1

acquired” or “return-to-local” (pressing the soft key/menu
button for GO TO LOCAL).

These events are tracked by the INR register which is reflected in
the SRE register as the INB summary bit in position 0. Since the
bit position 0 has the value 1, the command “*SRE 1” enables
the generation of SRQ whenever the INB summary bit is set.

In addition, the events of the INR register that may be

Note on Terms:

Note on Terms: The term “soft-key”, used here in

Note on Terms:Note on Terms:

reference to remote operations, is synonymous with “menu
button”, used exclusively in the accompanying Operator’s
Manual for front-panel operations. Both terms refer to the
column of seven buttons running parallel to the screen on
the oscilloscope front panel and the functions they control.

summarized in the INB bit must be specified. The event “new
signal acquired” corresponds to INE bit 0 (value 1) while the
event “return-to-local” is assigned to INE bit 2 (value 4). The total
sum is 1 + 4 = 5. Thus the command “INE 5” is needed:

CMD$=“INE 5;*SRE 1”

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GPIB

GPIB

GPIBGPIB

CALL IBWRT(SCOPE%,CMD$)

Example 2

Example 2 To assert SRQ when soft key 4 (fourth menu button from top

Example 2Example 2

of screen) is pressed.

The event “soft key 4 pressed” is tracked by the URR register.
Since the URR register is not directly reflected in STB but only in
the ESR register (URR, bit position 6), the ESE enable register
must be set first with the command “*ESE 64” to allow the URQ
setting to be reported in STB. An SRQ request will now be
generated provided that the ESB summary bit (bit position 5) in
the SRE enable register is set (“*SRE 32”):

CMD$=“*ESE 64;*SRE 32”
CALL IBWRT(SCOPE%,CMD$)

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Instrument Polls

Instrument Polls

Instrument PollsInstrument Polls

State transitions occurring within the instrument can be
remotely monitored by polling selected internal status registers
(see, too, Chapter 5). Four basic polling methods can be used
to detect the occurrence of a given event. These are
continuous, serial, parallel and *IST.

By far the simplest of these is continuous polling. The other three
are appropriate only when interrupt service routines (servicing
the SRQ line) are supported, or multiple devices on GPIB require
constant monitoring. Emphasizing the differences between these
methods, which are described below, the same example —
determining whether a new acquisition has taken place — is
presented in respect of each.

Continuous Poll

Continuous Poll Here, a status register is continuously monitored until a transition

Continuous PollContinuous Poll

is observed. This is the most straightforward method for
detecting state changes, but may be impracticable in certain
situations, especially with multiple device configurations.

In the following example, the event “new signal acquired” is
observed by continuously polling the INternal state change
Register (INR) until the corresponding bit (in this case bit 0, i.e.
value 1) is non-zero, indicating a new waveform has been
acquired. Reading INR clears this at the same time, obviating the
need for an additional clearing action after a non-zero value has
been detected. The command “CHDR OFF” instructs the
instrument to omit any command headers when responding to a
query, simplifying the decoding of the response. The instrument
will then send “1” instead of “INR 1”:

CMD$=“CHDR OFF”
CALL IBWRT(SCOPE%,CMD$)
MASK% = 1 ‘New Signal Bit has value 1’
LOOP% = 1
WHILE LOOP%

CMD$=“INR?”
CALL IBWRT(SCOPE%,CMD$)
CALL IBRD(SCOPE%,RD$)
NEWSIG% = VAL(RD$) AND MASK%

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GPIB

GPIB

GPIBGPIB

IF NEWSIG% = MASK% THEN LOOP% = 0

WEND

Serial Poll

Serial Poll Serial polling takes place once the SRQ interrupt line has been

Serial PollSerial Poll

asserted, and is only advantageous when there are several
instruments involved. The controller finds which device of a
number has generated the interrupt by inspecting the SRQ bit in
the STB register of each instrument. Because the service
request is based on an interrupt mechanism, serial polling offers
a reasonable compromise in terms of servicing speed in multiple­device configurations.

In the following example, the command “INE 1” enables the
event “new signal acquired” to be reported in the INR to the INB
bit of the status byte STB. The command “*SRE 1” enables the
INB of the status byte to generate an SRQ whenever it is set.
The function call IBWAIT instructs the computer to wait until one
of three conditions occurs: &H8000 in the mask (MASK%)
corresponds to a GPIB error, &H4000 to a timeout error, and
&H0800 to the detection of RQS (ReQuest for Service)
generated by the SRQ bit.

Whenever IBWAIT detects RQS it automatically performs a
serial poll to find out which instrument generated the interrupt. It
will only exit if there was a timeout or if the instrument
“SCOPE%” generated SRQ. The additional function call IBRSP
fetches the value of the status byte which may be further
interpreted. For this to function properly the value of “Disable
Auto Serial Polling” must be set to “off” in the GPIB handler (use
IBCONF.EXE to check):

CMD$=“*CLS; INE 1; *SRE 1”
CALL IBWRT(SCOPE%,CMD$)
MASK% = &HC800
CALL IBWAIT(SCOPE%,MASK%)
IF (IBSTA% AND &HC000) <> 0 THEN PRINT “GPIB
or Timeout Error” : STOP
CALL IBRSP(SCOPE%,SPR%)
PRINT “Status Byte =.”, SPR%

Board-level function calls can deal simultaneously with several
instruments attached to the same interface board. Refer to the
National Instruments manual.

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Note:

Note: After the serial poll is completed, the RQS bit in the

Note:Note:

STB status register is cleared. Note that the other STB register
bits remain set until they are cleared by means of a “*CLS”
command or the instrument is reset. If these bits are not
cleared, they cannot generate another interrupt.

Parallel Poll

Parallel Poll Like serial polling, this is only advantageous when there are several

Parallel PollParallel Poll

instruments. In parallel polling, the controller simultaneously reads
the Individual STatus bit (IST) of all the instruments to determine
which needs service. Because this method allows up to eight
different instruments to be polled at the same time, it is the fastest
way to identify state changes in instruments with this capability.

When a parallel poll is initiated, each instrument returns a status
bit over one of the DIO data lines. Devices may respond either
individually, using a separate DIO line, or collectively on a single
data line. Data-line assignments are made by the controller using
a Parallel Poll Configure (PPC) sequence.

In the following example, the command “INE 1” enables the
event “new signal acquired” in the INR to be reported to the INB
bit of the status byte STB. The PaRallel poll Enable register
(PRE) determines which events will be summarized in the IST
status bit. The command “*PRE 1” enables the INB bit to set the
IST bit whenever it is itself set. Once parallel polling has been
established, the parallel-poll status is examined until a change on
data bus line DI02 takes place.

Stage 1: Enable the INE and PRE registers, configure the
controller for parallel poll and instruct the oscilloscope to respond
on data line 2 (DI02)

CMD1$=“?_@$”
CALL IBCMD(BRD0%,CMD1$)
CMD$=“INE 1;*PRE 1”
CALL IBWRT(BRD0%,CMD$)
CMD4$=CHR$(&H5)+CHR$(&H69)+“?”
CALL IBCMD(BRD0%,CMD4$)

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GPIB

:

:

GPIB

GPIBGPIB

Stage 2: Parallel poll the instrument until DI02 is set

LOOP% = 1
WHILE LOOP%
CALL IBRPP(BRD0%,PPR%)
IF (PPR% AND &H2) = 2 THEN LOOP% = 0
WEND

Stage 3: Disable parallel polling (hex 15) and clear the parallel
poll register

CMD5$=CHR$(&H15)
CALL IBCMD(BRD0%,CMD5$)
CALL IBCMD(BRD0%,CMD1$)
CMD$=“*PRE 0”
CALL IBWRT(BRD0%,CMD$):

Note

Note: In the example above, board-level GPIB function

Note:Note

calls are used. It is assumed that the controller (board) and
scope (device) are respectively located at addresses 0 and

4. The listener and talker addresses for the controller and
oscilloscope are

Logic Device

Logic Device Listener Address

Logic DeviceLogic Device

ExternalController 32 ASCII<space>) 64 (ASCII @)

Oscilloscope 32+4=36 (ASCII $) 64+4=68 (ASCII D)

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Listener Address Talker Address

Listener AddressListener Address

Talker Address

Talker AddressTalker Address

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*IST Poll

*IST Poll The state of the Individual STatus bit (IST) returned in parallel

*IST Poll*IST Poll

polling can also be read by sending the “*IST?” query. To enable
this poll mode, the oscilloscope must be initialized as for parallel
polling by writing into the PRE register. Since *IST polling
emulates parallel polling, this method is applicable in all
instances where parallel polling is not supported by the controller.

Note:

Note:

Note:Note:

The characters “?” and “_” appearing in the command
strings stand for unlisten and untalk respectively. They
are used to set the devices to a “known” state.

To shorten the size of the program examples, device
talking and listening initialization instructions have been
grouped into character chains. They are:

CMD1$ = “?_@$” Unlisten, Untalk, PC talker, DSO
listener

The remote message code for executing a parallel
response in binary form is 01101PPP, where PPP
specifies the data line. Since data line 2 is selected, the
identification code is 001, which results in the code
01101001 (binary) or &H69 (hex). See Table 38 of the
IEEE 488-1978 Standard for further details.

In the following example, the command “INE 1” enables the
event “new signal acquired” in the INR to be reported to the INB
bit of the status byte STB. The command “*PRE 1” enables the
INB bit to set the IST bit whenever it is set. The command
“CHDR OFF” suppresses the command header in the
instrument’s response, simplifying the interpretation. The status
of the IST bit is then continuously monitored until set by the
instrument:

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