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150 Agilent N518xA, E8663B, E44x8C, and E82x7D Signal Generators Programming Guide
Programming the Status Register System
Accessing Status Register Information
The polling method works well if you do not need to know about changes the moment they occur.
Use polling in the following situations:
— when you use a programming language/development environment or IO interface that does not
support SRQ interrupts
— when you want to write a simple, single-purpose program and don’t want the added
complexity of setting up an SRQ handler
• The service request (SRQ) method
In the SRQ method (described in the following section), the signal generator takes a more active
role. It tells the controller when there has been a condition change without the controller asking.
Use the SRQ method to detect changes using the polling method, where the program must
repeatedly read the registers.
Use the SRQ method if you must know immediately when a condition changes. Use the SRQ
method in the following situations:
— when you need time-critical notification of changes
— when you are monitoring more than one device that supports SRQs
— when you need to have the controller do something else while waiting
— when you can’t afford the performance penalty inherent to polling
Using the Service Request (SRQ) Method
The programming language, I/O interface, and programming environment must support SRQ
interrupts (for example: BASIC or VISA used with GPIB and VXI-11 over the LAN). Using this
method, you must do the following:
1. Determine which bit monitors the condition.
2. Send commands to enable the bit that monitors the condition (transition registers).
3. Send commands to enable the summary bits that report the condition (event enable registers).
4. Send commands to enable the status byte register to monitor the condition.
5. Enable the controller to respond to service requests.
The controller responds to the SRQ as soon as it occurs. As a result, the time the controller would
otherwise have used to monitor the condition, as in a loop method, can be used to perform other
tasks. The application determines how the controller responds to the SRQ.
When a condition changes and that condition has been enabled, the request service summary (RQS)
bit in the status byte register is set. In order for the controller to respond to the change, the Service
Request Enable Register needs to be enabled for the bit(s) that will trigger the SRQ.
Generating a Service Request
The Service Request Enable Register lets you choose the bits in the Status Byte Register that will
trigger a service request. Send the *SRE <num> command where <num> is the sum of the decimal
values of the bits you want to enable.
For example, to enable bit 7 on the Status Byte Register (so that whenever the Standard Operation
Status register summary bit is set to 1, a service request is generated) send the command *SRE 128.
Refer to Figure 4-1 on page 140 through Figure 4-8 on page 147 for bit positions and values.