Agilent Technologies Agilent E5250A User Manual page 217

Command Reference
Status Reporting Structure
Figure 7-1 Status Reporting Structure of E5250A
The above figure shows Service Request Generation. When a condition occurs that
requires service, the instrument sets Request Service bit (RQS − bit6) of Status
Byte, and sends a Service Request (SRQ) via GPIB bus to the controller. So, the
controller can execute an interrupt service routine (must be in the program) that uses
a Serial Poll to read Status Byte of each instrument to determine which instrument
requested service. See "Status Byte Register" on page 7-50.
Agilent E5250A User's Guide, Edition 11 7-49