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The Service Request Process
When a register set causes its 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's SRQ process is initiated and the time the controller
reads the Status Byte register with a serial poll.)
The SRQ process sets the GPIB's SRQ line true. It also sets the Status Byte's request service
(RQS) bit to 1. Both actions are necessary to inform the controller the analyzer requires service.
Setting the SRQ line only informs the controller that some device on the bus requires service.
Setting the RQS bit allows the controller to determine that the Agilent 89400-series analyzer, in
particular, requires service.
If your program enables the controller to detect and respond to service requests, it should instruct
the controller to perform a serial poll when the GPIB's SRQ line is set true. Each device on the
bus returns the contents of its Status Byte register in response to this poll. The device whose
RQS bit is set to 1 is the device that requested service.
Notes
When you read the analyzer's Status Byte with a serial poll, the RQS bit is reset to
0. Other bits in the register are not affected.
Restarting a measurement (INIT) can cause the measuring bit to pulse low,
which causes an SRQ if the status register is configured to SRQ on
end-of-measurement. To avoid this:
1. INIT:CONT OFF
2. Set/enable status registers
3. Restart measurement (send INIT)
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