Output Queue; Error Queue - Keithley 2302 Instruction Manual

8-20 Status Structure

Output queue

The output queue holds data that pertains to the normal operation of the instrument. For
example, when a query command is sent, the response message is placed in the output queue.
When data is placed in the output queue, the message available (MAV) bit in the status byte
register sets. A data message is cleared from the output queue when it is read. The output queue
is considered cleared when it is empty. An empty output queue clears the MAV bit in the status
byte register.
A message is read from the output queue by addressing the power supply to talk after the
appropriate query is sent.
The following command sequence enables the MAV bit (B4) of the status byte register set,
and then causes an SRQ:
*SRE16
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Error queue

The error queue holds error and status messages. When an error or status event occurs, a
message that defines the error/status is placed in the error queue.
When a message is placed in the error queue, the error available (EAV) bit in the status byte
register is set. An error/status message is cleared from the error queue when it is read. The error
queue is considered cleared when it is empty. An empty error queue clears the EAV bit in the
status byte register.
The error queue holds up to 10 error/status messages. The commands to read the error queue
are listed in
is read and then removed from the queue. If the queue becomes full, the message "350, 'queue
overflow'" will occupy the last memory location. On power-up, the error queue is empty. When
empty, the message "0, No Error" is placed in the queue.
Messages in the error queue are preceded by a code number. Negative (-) numbers are used
for SCPI defined messages, and positive (+) numbers are used for Keithley defined messages.
The messages are listed in Appendix B.
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' Enable MAV bit of status byte to cause an SRQ.
' Send a query command to supply.
' Wait for an SRQ indicating ready to read.
' Read the query response.
Table 8-6. When you read a single message in the error queue, the "oldest" message