Tektronix Keithley 2651A Reference Manual page 904

Model 2651A High Power System SourceMeter® Instrument Reference Manual
Status byte and service request (SRQ)
Service requests (SRQs) allow an instrument to indicate that it needs attention or that some event
has occurred. When the controller receives an SRQ, it allows the controller to interrupt tasks to
perform other tasks in order to address the request for service.
For example, you might program your instrument to send an SRQ when:
•
All instrument operations are complete
•
An instrument error occurs
•
A specific operation has occurred
Two 8-bit registers control service requests: The Status Byte Register and the Service Request
Enable Register. See
registers.
Service requests affect GPIB and VXI-11 connections. On a GPIB connection, the SRQ line is
asserted. On a VXI-11 connection, an SRQ event is generated.
Status Byte Register
The summary messages from the status registers and queues are used to set or clear the appropriate
bits (B0, B1, B2, B3, B4, B5, and B7) of the Status Byte Register. These summary bits do not latch,
and their states (0 or 1) are dependent upon the summary messages (0 or 1). For example, if the
Standard Event Register is read, its register is cleared. As a result, its summary message resets to 0,
which then resets the ESB bit in the Status Byte Register.
The Status Byte Register also receives summary bits from itself, which sets the Master Summary
Status, or MSS, bit.
2651A-901-01 Rev. C October 2021
Status Byte Register (on page 15-15) for a description of the structure of these
Section 15: Status model
15-15