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3.5 IEEE-488 MESSAGE PROTOCOL
The equipment performs the basic Talker and Listener functions as specified in the IEEE-488
standard. It is also capable of sending a Service Request to the active IEEE-488 controller and
will respond with a status word when the Serial Poll Enable message is received.
The messages to and from the unit are ASCII character strings terminated with CR, LF and EOI.
The response time from command to acknowledge is 100 ms. maximum.
3.5.1 IEEE-488 MESSAGE FORMAT
The IEEE-488 message format is as follows:
COMMAND CODE - PARAMETERS
Commands are three ASCII characters preceded by an ASCII “?” or “$.” Commands preceded
by “?” are QUERY commands and those preceded by “$” are SET commands. QUERY
commands are used to examine system parameters while SET commands are intended to
modify system parameters.
SET commands do not affect the unit’s response when it is addressed to talk by the IEEE-488
controller.
QUERY commands determine the unit’s response when it is addressed to talk by the IEEE-488
controller. The context of the unit’s response remains in effect until another QUERY command
is received. The response to the Alarm Status Query command (?ALR) is in effect at power up
as the default format.
Parameters are all ASCII printable characters in the range of 20H to 7EH. Numeric parameters
are sent MSD first, LSD last. Values that do not adhere to the command format, or are beyond
the allowable range, will be ignored.
