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4-15
Remote Operation
Monitoring the Instrument
Output Queue
The output queue stores the instrument responses that are generated by cer-
tain commands and queries that you send to the instrument. 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. The method used to read the output queue depends upon the
programming language and environment. For example, with HP Basic, the
output queue may be read using the
ENTER
statement.
Error Queue
As errors are detected, they are placed in an error queue. Instrument specific
errors are indicated by positive values. General errors have negative values.
You can clear the error queue by reading its contents, sending the
*CLS
com-
mand, or by cycling the instrument’s power. The error queue is first in, first
out. If the error queue overflows, the last error in the queue is replaced with
error -350, “Queue overflow.” Any time the queue overflows, the least recent
errors remain in the queue, and the most recent error is discarded. The length
of the instrument’s error queue is 30 (29 positions for the error messages, and
1 position for the “Queue overflow” message). Querying errors 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.”
Command Use
*CLS
common command
Clears the error queue (and all event registers).
SYSTem:ERRor?
Returns and removes the oldest error from the
head of the queue.
book.book Page 15 Monday, January 31, 2000 10:34 AM