SECTION 4
IEEE-488 Reference
4.1 INTRODUCTION
The IEEE&?8 bus Is an instrumentation data bus with
hardware and programming standards originally
adopted by the IEEE (Institute of Electrical and Electronic
Engineers) in 1975 and given the IEEE-488 designation.
In 1978, standards were upgraded Into the IEEE-488-1978
standards. The Models 486 and 487 conform to these
standards.
This section contab reference Information on program-
ming the Model 486/487 over the IEEE-488 bus. Detailed
instructions for all programmable functions are in-
cluded, however, information concerning operating
modes presented elsewhere is not repeated. Refer to Sec-
tions 2 and 3 for information not found in this section.
Additional information on the IEEE-488 bus is located in
the appendices.
NOTE
The programmed examples used in this sec-
tion are written Hewlett Packard BASIC ver-
sion 4.0. This language was chosen because of
its versatility in con!ndling the IEEE-488 bus.
4.2 DEVICE-DEPENDENT COMMAND
PROGRAMMING
IEEE-488 device-dependent commands are the most im-
portant co mmands associated with instrument program-
ming because they control most instrument operating
modes. The IEEE-488 bus actually treats these commands
as data, in that they are sent with ‘dw ATN line false.
Most Model 486/487 front panel operations (such as
range selection) as well as some operations not available
from the front panel (like SRQ and terminator) can be
program&d with these commands.
Command Syntax-Each command is made up of a sin-
gle ASCII capital letter followed by one or more numbers
orlettersrepresentinganoption ornumericparameter of
that command. For example, the integration time can be
set over the bus by sending the letter “S” foIlowed by a
number representing the integration time option. SOX
would be sent to program a 1.6msec integration time.
Sending a command without an option (such as RX) is the
same as not sending a command. However, it wiU take
time to process the command.
Ifacommandappears more thanonceinanX-terminated
s&g, only the last occurrence of the command is exe-
cuted -the others are ignored.
Multiple Options -
Some
commands have two or more
options that must be separated by commas. For example,
a V5,OJX command programs the voltage source of the
Model 487. In this case, the 5 is the value of the voltage
source (+5v), 0 is the voltage source range (SOW, and the
1 is the current limit option (2mA).
Options of a multiple option command may be defaulted
as demonstrated in the following examples:
VlOX Set V-source to 1OV. Range and l-limit will de-
fault to currently programmed parameters.
V60,lX Set V-source to 60V on the 5DDV range, and de-
fault l-limit.
v,ox Default V-source, select5OVrange, and default
l-limit.
v,,ox
Default V-source, default range, and set I-limit
to 25H.
Multiple Commands -A number of commands can be
grouped together in one command string, which is gen-
erally terminated by the “X” character. This character
tells the inskument to execute the command or com-
mand string, as desaibed in paragraph 4.2.22. Com-
mands sent without the execute character will not be exe-
cuted at that particular time, but they will be stored
4-1
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