Specifications

556 Appendix B
GPIB Status Report System
General Model of Status Registers
General Model of Status Registers
The E4991A has a status report system that notifies users of its states.
Figure B-1 General Model of Status Registers
The status report system has a hierarchical structure as shown in Figure B-1. When the
instrument meets a certain condition, the corresponding bit in the appropriate event register
is set to 1. By monitoring event registers, users can grasp the state of the instrument.
If a bit in an event register is set to 1 and the corresponding bit (indicated by arrows in
Figure B-1) in the enable register in the upper level is also set to 1, the summary bit of the
Status Byte Register is set to 1. The state of the Status Byte Register can be obtained
through serial poll.
If a bit in the Service Request Enable Register is set 1, a service request (SRQ) occurs
when the corresponding bit in the Status Byte Register is set to 1. The SRQ informs the
controller that the E4991A is requesting a service and a program to handle interrupt when
the SRQ is generated. For how to use the SRQ, see
“Using the Status Register” on
page 112 or “Using Status Report Mechanism” on page 203.