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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

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.

Chapter 5 Remote Interface Reference

The SCPI Status System

278

HP 34970A User Manual

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