Agilent Technologies ESA-E E4401B, User'S/Programmer'S Reference

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202 Chapter 4
Status Registers
Use Status Registers to Determine the State of Analyzer Events and Conditions
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NOTE
If you are using the status bits and the analyzer mode is changed, the status bits
should be read, and any error conditions resolved, prior to switching modes. Error
conditions that exist prior to switching modes cannot be detected using the
condition registers after the mode change. This is true unless they recur after the
mode change, although transitions of these conditions can be detected using the
event registers.
Changing modes resets all SCPI status registers and mask registers to their
power-on defaults. Hence any event or condition register masks must be
re-established after a mode change. Also note that the power up status bit is set by
any mode change, since that is the default state after power up.
Status Subsystem Commands
Individual status registers can be set and queried using the commands in the STATus subsystem in
Chapter 5, “Remote Command Reference.” in this guide. There are two methods used to
programmatically detect and manage error conditions or changes in analyzer status. Either method
allows you to monitor one or more conditions. The two methods are:
• The Polling Method
• The Service Request (SRQ) Method
The Polling Method
In the polling method, the analyzer has a passive role. It only tells the controller that conditions have
changed when the controller asks the right question. The polling method works well if you do not need to
know about changes the moment they occur. This method is very efficient.
Use the polling method when either:
— your programming language/development environment does not support SRQ interrupts
— 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
The SRQ method allows timely communication of information without requiring continuous controller
involvement. Using this method, the analyzer takes a more active role. It tells the controller when there
has been a condition change without the controller asking. The SRQ method should be used if you must
know immediately when a condition changes. This is in contrast to the polling method, which requires
the program to repeatedly read the registers to detect a change.