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) to select which summary bits will set the
low-level
IEEE-488 SRQ signal. When the status byte “request service”
bit (bit 6) is set, an
IEEE-488 SRQ 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 one
with bit 6 set in its status byte). The request service bit is only cleared
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.
4
Chapter 4 Remote Interface Reference
The SCPI Status Model
137
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