Agilent Technologies Understanding Agilent Service Request and SCPI Status Model for Effective Instrument Control

Chapter 4 Remote Interface Reference

The SCPI Status Model

Using Service Request (SRQ) and Serial POLL

You must configure your bus controller to respond to the IEEE-488service 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-488serial 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-488serial 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	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.

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