Programming instructions

Table Of Contents

Programming the Status Register System

Accessing Status Register Information

Chapter 3 107

Using the Service Request (SRQ) Method

The programming language, I/O interface, and programming environment must support SRQ

interrupts (example: BASIC used with GPIB.) Using this method, you must do the following:

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 commands to enable the bit that monitors 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 signal generator sets its RQS bit and asserts an SRQ. The

controller is informed of the change as soon as it occurs. As a result, the time the controller

would otherwise have used to monitor the condition can be used to perform other tasks. The

program determines how the controller responds to the SRQ.

Generating a Service Request To use the SRQ method, you must understand how service

requests are generated. The *SRE command sets the bits in the Service Request Enable

in the Status Byte Register to set high (from 0 to 1) when there is a change in instrument

status. When a Status Byte Register bit is set high, it will enable the setting (0 to 1) of the

request service (RQS) bit (bit 6). Refer to Figure 3-1 on page 103 for a visual representation of

this process.

This 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 signal generator does not have a service request pending.

A service request is considered to be pending between the time the signal generator’s SRQ

process is initiated and the time the controller reads the status byte register.

NOTE Multiple Status Byte Register bits can assert an SRQ, however only one bit at a

time can set the RQS bit. All bits that are asserting an SRQ will be read as part

of the status byte when queried or serial polled.

The SRQ process asserts SRQ as true and sets the status byte’s RQS bit to 1. Both actions are

necessary to inform the controller that the signal generator requires service. Asserting SRQ

only informs the controller that some device on the bus requires service. Setting the RQS bit

allows the controller to determine which signal generator requires service.