1-14 Programmer’s Guide
Introduction to GPIB Programming
Programming Fundamentals
GPIB Queues
Queues enhance the exchange of messages between the analyzer and
other devices on the bus. The analyzer contains the following:
• an input queue
• an error queue
• an output queue
Input Queue
The input queue temporarily stores the following until they are read by
the analyzer's command parser:
• device commands and queries
• the GPIB END message (EOI asserted while the last data byte is on
the bus)
The input queue also makes it possible for a controller to send multiple
program messages to the analyzer without regard to the amount of time
required to parse and execute those messages. The queue holds up to 128
bytes. It is cleared when the following actions occur:
• the analyzer is turned on
• the Device Clear (DCL) or Selected Device Clear (SDC) command is
received
Error Queue
The error queue temporarily stores up to 20 error messages. Each time
the analyzer detects an error, it places a message in the queue. When you
send the SYST:ERR? query, one message is moved from the error queue
to the output queue so it can be read by the controller. Error messages
are delivered to the output queue in the order they were received.
The error queue is cleared when the following actions occur:
• all the error messages are read using the SYST:ERR? query
• the analyzer is turned on
• the *CLS command is received
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