Using Service Request (SRQ) and Serial POLL
You must configure your bus controller to respond to the IEEE-488
service request (
SRQ) interrupt to use this capability. Use the Status
Byte enable register (*SRE command) to select which summary bits will
set the low-level
IEEE-488 service request signal. When bit 6 (request
service) is set in the Status Byte, an
IEEE-488 service request interrupt
message is automatically sent to the bus controller. The bus controller
may then poll the instruments on the bus to identify which one
requested service (the instrument with bit 6 set in its Status Byte).
The request service bit is cleared only by reading the Status Byte using
an IEEE-488 serial poll or by reading the event register whose summary
bit is causing the service request.
To read the Status Byte summary register, send the
IEEE-488 serial poll
message. Querying the summary register will return a decimal value
which corresponds to the binary-weighted sum of the bits set in the
register. Serial poll will automatically clear the “request service” bit in
the Status Byte summary register. No other bits are affected.
Performing a serial poll will not affect instrument throughput.
Caution
The IEEE-488.2 standard does not ensure synchronization between your
bus controller program and the instrument. Use the *OPC? command to
guarantee that commands previously sent to the instrument have
completed. Executing a serial poll before a *RST, *CLS, or other
commands have completed can cause previous conditions to be reported.
Chapter 4 Remote Interface Reference
The SCPI Status Registers
204
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