Tektronix Keithley 2651A Reference Manual page 907

Section 15: Status model
Serial polling and SRQ
Any enabled event summary bit that goes from 0 to 1 sets bit B6 and generates a service request
(SRQ).
In your test program, you can periodically read the Status Byte to check if an SRQ occurred and what
caused it. If an SRQ occurred, the program can, for example, branch to an appropriate subroutine
that services the request.
SRQs can be managed by the serial poll sequence of the instrument. 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 B6 for an SRQ occurrence that is generated by other event types.
The serial poll does not clear the low-level registers that caused the SRQ to occur. You must clear the
low-level registers explicitly. Refer to
For common commands and TSP commands, B6 is the MSS (Message Summary Status) bit. The
serial poll does not clear the MSS bit. The MSS bit remains set until all enabled Status Byte Register
summary bits are reset.
SPE, SPD (serial polling)
For the GPIB interface only, the SPE and SPD general bus commands are used to serial poll the High
Power System SourceMeter
obtains the serial poll byte (status byte). Typically, serial polling is used by the controller to determine
which of several instruments has requested service with the SRQ line.
15-18
Model 2651A High Power System SourceMeter® Instrument Reference Manual
Clearing registers
® Instrument (see General bus commands
(on page 15-13).
(on page 2-86)). Serial polling
2651A-901-01 Rev. C October 2021