Serial Polling And Srq - Keithley 708B Reference Manual

Models 707B and 708B Switching Matrix Reference Manual
The bits of the Status Byte Register are described as follows:
•
Bit B0, Measurement Summary Bit (MSB): Set summary bit indicates that an enabled
measurement event has occurred.
•
Bit B1, System Summary Bit (SSB): Set summary bit indicates that an enabled system event
has occurred.
•
Bit B2, Error Available (EAV): Set bit indicates that an error or status message is present in the
Error Queue.
•
Bit B3, Questionable Summary Bit (QSB): Set summary bit indicates that an enabled
questionable event has occurred.
•
Bit B4, Message Available (MAV): Set bit indicates that a response message is present in the
Output Queue.
•
Bit B5, Event Summary Bit (ESB): Set summary bit indicates that an enabled standard event
has occurred.
•
Bit B6, Request Service (RQS)/Master Summary Status (MSS): Set bit indicates that an
enabled summary bit of the Status Byte Register is set. Depending on how it is used, Bit B6 of the
Status Byte Register is either the Request for Service (RQS) bit or the Master Summary Status
(MSS) bit:
•
When using the GPIB serial poll sequence of the Models 707B and 708B to obtain the status byte
(serial poll byte), B6 is the RQS bit. See
serial poll sequence.
•
When using the *STB? common command or status.condition
commands
•
Bit B7, Operation Summary (OSB): Set summary bit indicates that an enabled operation event
has occurred.

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 Switching Matrix. 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 MSS. The MSS bit stays set until all Status Byte register summary bits are reset.
707B-901-01 Rev. A / August 2010
(on page C-18) to read the status byte, B6 is the MSS bit.
Serial polling and SRQ (on page C-17) for details on using the
Status byte and service request
Appendix C: Status model
C-17