Appendix C: Status model
Models 707B and 708B Switching Matrix Reference Manual
C-18
707B-901-01 Rev. B / January 2015
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, USB, or VXI-11 serial poll sequence of the Models 707B and 708B to obtain the
status byte (serial poll byte), B6 is the RQS bit. See
(on page C-18) for details
on using the serial poll sequence.
•
When using the *STB? common command or status.condition
Status byte and service request
(on page C-20) to read the status byte, B6 is the MSS bit.
•
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 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 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 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.
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
Switching Matrix. 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.
