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Protocol Overview
Protocol Operation
HP 1662B11653B
Programming Reference
The instrument and controller communicate using < program message > s
and < response message > s. These messages serve as the containers into
which sets of program commands or instrument responses are placed.
response to a query message. A < query message > is defined as being a
instrument will only talk when it has received a valid query message, and
therefore has something to say. The controller should only attempt to
read a response after sending a complete query message, but before
sending another
program message > . The basic rule to remember is
c
that the instrument will only talk when prompted to, and it then expects to
talk before being told to do something else.
When the instrument is turned on, the input buffer and output queue are
cleared, and the parser is reset to the root level of the command tree.
The instrument and the controller communicate by exchanging complete
controller should always terminate a < program message > before
attempting to read a response. The instrument will terminate -z response
message > s except during a hardcopy output.
If a query message is sent, the next message passing over the bus should
be the < response message > . The controller should always read the
complete < response message > associated with a query message before
sending another < program message > to the same instrument.
The instrument allows the controller to send multiple queries in one query
message. This is referred to as sending a "compound query." As will be
noted later in this appendix, multiple queries in a query message are
separated by semicolons. The responses to each of the queries in a
compound query will also be separated by semicolons.
Commands are executed in the order they are received.
Message Communication and System Functions
A-3
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