Using The Service Request (Srq) Method; Generating A Service Request - Agilent Technologies ESA-E Series Programmer's Manual

Status Registers
Use Status Registers to Determine the State of Analyzer Events and Conditions
— you are monitoring more than one device which supports SRQs
— you need to have the controller do something else while the analyzer
is making a measurement
— you can't afford the performance penalty inherent to polling

Using the Service Request (SRQ) Method

Your language, bus, and programming environment must be able to
support SRQ interrupts (for example, using C and C++ with the GPIB).
When you monitor a condition with the SRQ method, you must
establish the following parameters:
1. Determine which bit monitors the condition.
2. Determine how that bit reports to the request service (RQS) bit of
the status byte.
3. Send GPIB commands to enable the bits that monitor the condition
and to enable the summary bits that report the condition to the RQS
bit.
4. Enable the controller to respond to service requests.
When the condition changes, the analyzer sets the RQS bit and the
GPIB SRQ line. The controller is informed of the change as soon as it
occurs. The time the controller would otherwise have used to monitor
the condition can now be used to perform other tasks. Your program
also determines how the controller responds to the SRQ.

Generating a Service Request

Before using the SRQ method of generating a service request, first
become familiar with how service requests are generated. Bit 6 of the
status byte register is the request service summary (RQS) bit. The RQS
bit is set whenever there is a change in the register bit that it has been
configured to monitor. The RQS bit will remain set until the condition
that caused it is cleared. It can be queried without erasing the contents
using the *STB? command. Configure the RQS function using the *SRE
command.
When a register set causes a summary bit in the status byte to change
from 0 to 1, the analyzer can initiate the service request (SRQ) process.
However, the process is only initiated if both of the following conditions
are true:
• The corresponding bit of the service request enable register is also
set to 1.
• The analyzer does not have a service request pending. (A service
request is considered to be pending between the time the analyzer
SRQ process is initiated, and the time the controller reads the status
byte register.)
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