Model 2651A High Power System SourceMeter® Instrument Reference Manual Appendix E: Status model
2651A-901-01 Rev. A / March 2011 E-17
Serial polling and SRQ
Any enabled event summary bit that goes from 0 to 1 will set bit B6 and generate a service request
(SRQ).
In your test program, you can periodically read the Status Byte to check if an SRQ has occurred and
what caused it. If an SRQ occurs, 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 High Power System SourceMeter
®
Instrument. If an SRQ does not occur, bit B6 (RQS) of the Status Byte Register will remain cleared,
and the program will simply proceed normally after the serial poll is performed. If an SRQ does occur,
bit B6 of the Status Byte Register will 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 generated by other event types.
For common and script commands, B6 is the MSS (Message Summary Status) bit. The serial poll
does not clear the MSS bit. The MSS bit stays set until all 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
®
Instrument (see General bus commands (on page 2-78)). 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.
Status byte and service request commands
The commands to program and read the Status Byte Register and Service Request Enable Register
are listed in Status byte and service request commands
(on page E-17). Note that the table includes
both common commands and their script command equivalents. For details on programming and
reading registers, see Programming enable and transition registers
(on page E-13) and Reading
registers (on page E-14).
To reset the bits of the Service Request Enable Register to 0, use 0 as the parameter value for the
command (for example, *SRE 0 or status.request_enable = 0).
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