A-12
A
A1.2.3 IEEE 488.2 Common Commands
The IEEE 488.2 Standard also mandated a list of required and optional
Common Commands that all 488.2 devices could support. All of the
Common Commands start with an asterisk. Commands that end with
a question mark are queries. Query responses can be an ASCII
number or an ASCII string. Other numerical formats are legal as long
as the device supports the required ASCII format. Table A-2 lists the
IEEE 488.2 Common Commands.
A1.2.4 IEEE 488.2 Differences From IEEE 488.1
The user who is familiar with the older 488.1 devices should take the
following differences into account when programming a 488.2 device.
A 488.2 device outputs the Status Byte Register contents plus the RQS
bit in response to a serial poll. The RQS bit is reset by the serial poll.
The same 488.2 device outputs the Status Byte Register contents plus
the MSS bit in response to a *STB? query. The MSS bit is cleared
when the condition is cleared.
488.2 restricts the Device Clear to only clearing the device's buffers
and pending operations. It does not clear the Status Reporting
Structure or the output lines. Use *CLS to clear the Status Structure
and *RST or *RCL to reset the outputs.
488.2 commands are really special data messages and are executed by
the device's parser. Always allow sufficient time for the parser to
execute the commands before sending the device a 488.1 command.
i.e. a Device Clear sent too soon will erase any pending commands and
reset the parser.
Enable Register values are only saved and restored if the *PSC
command is 0. A *PSC command of 1 causes zeros to be loaded into
the enable registers when the unit is next reset or powered on.
