Agilent Technologies ESA-E Series Programmer's Manual page 41

Status Registers
Use Status Registers to Determine the State of Analyzer Events and Condition s
NOTE
If you are using the status bits and the analyzer mode is changed, th e
status bits should be read, and any error conditions resolved, prior t o
switching modes . Error conditions that exist prior to switching mode s
cannot be detected using the condition registers after the mode change .
This is true unless they recur after the mode change, althoug h
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 stat e
after power up.
Status Subsystem Command s
Individual status registers can be set and queried using the command s
in the STATus subsystem in Chapter 5, "Language Reference" in thi s
guide . There are two methods used to programmatically detect an d
manage error conditions or changes in analyzer status. Either metho d
allows you to monitor one or more conditions . The two methods are:
• The Polling Method
• The Service Request (SRQ) Method
The
rowing
Method
In the polling method, the analyzer has a passive role . It only tells the
controller that conditions have changed when the controller asks th e
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 no t
support SRQ interrupts
- you want to write a simple, single-purpose program and don ' t wan t
the added complexity of setting up an SRQ handler
The Service Request (SRQ) Metho d
The SRQ method allows timely communication of information withou t
requiring continuous controller involvement . Using this method, th e
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 conditio n
changes . This is in contrast to the polling method, which requires th e
program to repeatedly read the registers to detect a change.
Use the SRQ method when either :
- you need time-critical notification of change s
Chapter 2 2-7