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100 Chapter 7 Using GPIB Interface
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 802 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 802 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 802 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