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Chapter 4 Remote Interface Reference
The SCPI Status Model
Using Service Request (
) and Serial
SRQ
POLL
You must configure your bus controller to respond to the
IEEE-488
service request (
) interrupt to use this capability. Use the status
SRQ
byte enable register (
) to select which summary bits will set the
SRE
low-level
signal. When the status byte "request service"
IEEE-488 SRQ
bit (bit 6) is set, an
interrupt message is automatically
IEEE-488 SRQ
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
serial poll or by reading
IEEE-488
the event register whose summary bit is causing the service request.
To read the status byte summary register, send the
serial poll
IEEE-488
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
4
a serial poll will not affect instrument throughput.
C a u t i o n
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.
137
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