Remote Operation
Retrieval of Device Status Information 5
5-11
5-21. Request Service (RQS)
5-22. Reasons for Requesting Service
There are two main reasons for the application program to request service from the
controller:
• When the instrument’s message exchange interface is programmed to report a system
programming error.
• When the instrument’s is programmed to report significant events by RQS.
The significant events vary between types of devices; thus there is a class of events which
are known as Device Specific. The device designer determines these.
5-23. RQS in the IEEE 488.2 Model
The application programmer can enable or disable the event(s) which are required to
originate an RQS at particular stages of the application program. The IEEE 488.2 model is
extended to incorporate a flexible SCPI status reporting structure in which the requirements
of the device designer and application programmer are both met.
This structure is described in “Retrieval of Device Status Information”.
5-24. Retrieval of Device Status Information
For any remotely operated system, the provision of up to date information about the
performance of the system is of major importance. In the case of systems, which operate
under automatic control, the controller requires the necessary feedback to enable it to
progress the task; any break in the continuity of the process can have serious results.
When developing an application program, the programmer needs to test and revise it,
knowing its effects. Confidence that the program elements are couched in the correct
grammar and syntax (and that the program commands and queries are thus being accepted
and acted upon), helps to reduce the number of iterations needed to confirm and develop the
viability of the whole program. Such information is given in the following pages.
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