Agilent Technologies 34970A manual Using Service Request SRQ and Serial Poll

Chapter 5 Remote Interface Reference

The SCPI Status System

Using Service Request (SRQ) and Serial Poll

You must configure your computer 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 condition bits will assert the IEEE-488 SRQ line. If bit 6 (RQS) transitions from a “0” to a “1”, then an IEEE-488 service request message is sent to your computer. The computer may then poll the instruments on the interface bus to identify which one is asserting the service request line (the instrument with bit 6 set in its Serial Poll response).

Note: When a Serial Poll is issued, bit 6 (RQS) is cleared in the Status Byte (no other bits are affected) and the service request line is cleared.

To read the Status Byte condition register, send an IEEE-488 Serial Poll message. Querying the condition register will return a decimal value which corresponds to the binary-weighted sum of the bits set in the register. Performing a Serial Poll will not affect measurement throughput.

Note: Unlike other commands, a Serial Poll is executed immediately. Therefore, the status indicated by a Serial Poll may not necessarily indicate the affect of the most recent command. Use the *OPC? command to guarantee that commands previously sent to the instrument have completed before executing a Serial Poll.

Using *STB? to Read the Status Byte

The *STB? command is similar to a Serial Poll but it is processed like any other instrument command. The *STB? command returns the same result as a Serial Poll but bit 6 is not cleared as long as the enabled conditions remain.

The *STB? command is not handled automatically by the IEEE-488 bus interface hardware and will be executed only after previous commands have completed. You cannot clear an SRQ using the *STB? command.

278