Quantum Data 881, User Manual

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882 Video Test Instrument User Guide (Rev A.35) 209
Queries and commands
The GPIB interface is an ASCII command line interface like the RS-232 command line
interface. The communications protocol is per IEEE-488.2 specification. Queries and
commands consist of four ASCII upper/lower case characters. Commands do not require
a response from the generator, while queries cause the generator to respond with the
required data.
You can send multiple commands on the same line by separating the commands with a
semicolon (;) followed by a terminator. A terminator is defined as the NL character (ASCII
10), or EOI sent with the last byte of the command. The generator will not parse any
commands received until a terminator is received. All commands are executed
sequentially; that is, when a command is parsed it is allowed to finish execution before the
next command is parsed, as illustrated in the following figure.
Commands
Commands instruct the generator to set a parameter to the value given or perform some
function not requiring any additional data. Commands which have an asterisk (*) as their
first character are common commands as defined by the IEEE-488.2 standard and
generally operate the same in all instruments. All commands are listed and described in
Appendix A, “ Command Reference .”
Commands which do not require any additional data from the controller are self-contained
and should be followed by either a message separator (;) or message terminator. Any
other characters (except whitespace characters) will cause a command error.
Commands which require numeric data must be followed by at least one separator
character (whitespace), and then the data. Numeric data sent with a command is in
decimal format. Numeric data can be represented in one of three methods: integer,
floating point, or scaled floating point.
Message Terminator
Separator ( ; )
Program Message Syntax
Command/Query
Header
Separator
( ; )
Data
Separator
(white space)
Message Unit Syntax