Agilent Technologies N8201A Service Manual download pdf (Page 103)

Programming the Status Register System 4

Agilent N8211A/N8212A Performance Upconverter Synthetic Instrument Module, 250 kHz to 20 / 40 GHz 103

The polling method

In the polling method, the N8211A/N8212A has a passive role. It tells the controller that

conditions have changed only when the controller asks the right question. This is

accomplished by a program loop that continually sends a query.

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 do not 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 N8211A/N8212A 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 cannot 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 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.

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Agilent Technologies N8201A Service Manual Page 103