Agilent Technologies Model A.08.xx manual Status Subsystem Commands, Polling Method

Status Registers

Use Status Registers to Determine the State of Analyzer Events and Conditions

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, “Language 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.

62 Chapter 2