HP E4401B, Руководство программиста

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2-2 Chapter 2
HP ESA Status Registers
Using the Analyzer Status Registers
Using the Analyzer Status Registers
The status system is comprised of multiple registers which are
arranged in a hierarchical order. The lower-priority status registers
propagate their data to the higher-priority registers in the data
structures by means of summary bits. The status byte register is at the
top of the hierarchy and contains the general status information for the
analyzer events and conditions. All other individual registers are used
to determine the specific events or conditions.
You can determine the state of certain analyzer hardware and firmware
events and conditions by programming the status register system.
Figure 2-1 shows all the analyzer status registers and their hierarchy.
Why Would You Use the Status Registers?
Your program often needs to be able to detect and manage error
conditions or changes in analyzer status. There are two methods you
can use to programmatically access the information in status registers:
• The polling method
• The service request (SRQ) 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. In the SRQ method, the analyzer takes a more active
role. It tells the controller when there has been a condition change
without the controller asking. Either method allows you to monitor one
or more conditions.
The polling method works well if you do not need to know about
changes the moment they occur. The SRQ method should be used if you
must know immediately when a condition changes. To detect a change
using the polling method, the program must repeatedly read the
registers.
Use the SRQ method when:
— you need time-critical notification of changes
— you are monitoring more than one device which supports SRQs
— you need to have the controller do something else while waiting
— you can’t afford the performance penalty inherent to polling
Use polling when:
— 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
To monitor a condition: