High Voltage SourceMeter Instrument Reference Manual Appendix B:
2470-901-01 Rev. A / May 2019 B-13
Queues
The instrument includes an Output Queue and an Error Queue. The Output Queue holds messages
from readings and responses. The Error Queue holds error event messages from the event log. Both
are first-in, first-out (FIFO) registers.
Output Queue
The output queue holds response messages to SCPI query and TSP print() commands.
When data is placed in the Output Queue, the Message Available (MAV) bit in the Status Byte
Register is set. The bit is cleared when the Output Queue is empty.
To clear data from the Output Queue, read the messages. To read a message from the Output
Queue, address the instrument to talk after the appropriate query is sent.
Error Queue
The Error Queue holds any error events that are posted in the event log. When an error event occurs,
it is posted to the Error Queue, which sets the Error Available (EAV) bit in the Status Byte Register.
The instrument clears error event messages from the event log when it retrieves the event log. When
the error event messages are cleared from the event log, the EAV bit in the Status Byte Register is
cleared.
You can clear the Error Queue by sending the common command *CLS or the TSP command
status.clear(). Note that status.clear() also clears all event registers.
For information regarding the event log, see Using the event log (on page 3-50
).
Serial polling and SRQ
Any enabled event summary bit that goes from 0 to 1 sets bit B6 and generates a service request
(SRQ).
In your test program, you can periodically read the Status Byte to check if an SRQ occurred and what
caused it. If an SRQ occurred, the program can, for example, branch to an appropriate subroutine
that will service the request.
SRQs can be managed by the serial poll sequence of the instrument. If an SRQ does not occur, bit
B6 (RQS) of the Status Byte Register remains cleared, and the program proceeds normally after the
serial poll is performed. If an SRQ does occur, bit B6 of the Status Byte Register is set, and the
program can branch to a service subroutine when the SRQ is detected by the serial poll.
The serial poll automatically resets RQS of the Status Byte Register. This allows subsequent serial
polls to monitor bit B6 for an SRQ occurrence that is generated by other event types.
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