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Status Reporting
Error Queue
Error Queue
As errors are detected, they are placed in an error queue. This queue is a first-
in, first-out queue. If the error queue overflows, the last error in the queue is
replaced with error -350, "Queue overflow." Any time the queue overflows, the
oldest errors remain in the queue, and the most recent error is discarded. The
length of the oscilloscope's error queue is 30 (29 positions for the error
messages, and 1 position for the "Queue overflow" message).
The error queue is read with the :SYSTEM:ERROR? query. Executing this query
reads and removes the oldest error from the head of the queue, which opens a
position at the tail of the queue for a new error. When all the errors have been
read from the queue, subsequent error queries return 0, "No error."
The error queue is cleared when any of these events occur:
• When the oscilloscope is powered up.
• When the oscilloscope receives the *CLS common command.
• When the last item is read from the error queue.
For more information on reading the error queue, refer to the
:SYSTEM:ERROR? query in the System Commands chapter. For a complete
list of error messages, refer to the chapter, "Error Messages."
Output Queue
The output queue stores the oscilloscope-to-computer responses that are
generated by certain oscilloscope commands and queries. The output queue
generates the Message Available summary bit when the output queue contains
one or more bytes. This summary bit sets the MAV bit (bit 4) in the Status Byte
Register. You may read the output queue with the HP Basic ENTER statement.
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