Appendix C: Status model
Series 3700A System Switch/Multimeter Reference Manual
C-18
3700AS-901-01 Rev. D/June 2018
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 occured, the program can, for example, branch to an appropriate subroutine that
will service 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
(on page C-13).
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
System Switch/Multimeter. Serial polling 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.
Service requests
Service requests (SRQs) affect both the GPIB and the VXI-11 connections. On a GPIB connection,
the SRQ line is asserted. On a VXI-11 connection, an SRQ event is generated.
