Serial Poll And Srq - Keithley 6517B Reference Manual

Section 13: Status structure Model 6517B Electrometer Reference Manual

Serial poll and SRQ

Any enabled event summary bit that goes from 0 to 1 sets RQS and generate a service request
(SRQ). The user's test program can periodically read the status byte register to check to see if a
service request (SRQ) has occurred and what caused it. In the event of an SRQ, the program can, for
example, branch to an appropriate subroutine that services the request. Typically, service requests
(SRQs) are managed by the serial poll sequence of the Model 6517B. If an SRQ does not occur, Bit
B6 (RQS) of the status byte register remains cleared, and the program proceeds normally after the
serial poll is performed. If an SRQ does occur, Bit B6 of the status byte register is set and the
program can branch to a service subroutine when the SRQ is detected by the serial poll.
The serial poll automatically resets RQS of the status byte register. This allows subsequent serial
polls to monitor Bit 6 for an SRQ occurrence generated by other event types. After a serial poll, the
same event can cause another SRQ, even if the event register which caused the first SRQ has not
been cleared.
A serial poll clears RQS but does not clear MSS. The MSS bit stays set until all status byte event
summary bits are cleared.
13-14 6517B-901-01 Rev. C / August 2015