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Section 6: 9100 System Operation — SCPI Language
Final Width = 215mm
6.4.3.5
Outgoing Responses
The Response Formatter derives its information from Response Data (being supplied
by the Functions and Facilities block) and valid Query Requests. From these it builds
Response Message Elements, which are placed as a Response Message into the Output
Queue.
The Output Queue acts as a store for outgoing messages until they are read over the
system bus by the application program. For as long as the output queue holds one or more
bytes, it reports the fact by setting true bit 4 (Message Available - MAV) of the Status Byte
register. Bit 4 is set false when the output queue is empty (refer to Sub-Section 6.5
‘Retrieval of Device Status Information’).
6.4.3.6
‘Query Error’
This is an indication that the application program is following an inappropriate message
exchange protocol, resulting in the Interrupted, Unterminated or Deadlocked condition:
Refer to 'Bit 2' in paras 6.5.3.5.
The Standard document defines the 9100’s response, part of which is to set true bit 2
(QYE) of the Standard-defined Event Status register.
6.4.4
Request Service (RQS)
6.4.4.1
Reasons for Requesting Service
There are two main reasons for the application program to request service from the
controller:
•
When the 9100 message exchange interface is programmed to report a system
programming error;
•
When the 9100 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’. These are determined by the device designer.
6.4.4.2
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 Sub-Section 6.5, dealing with ‘Retrieval of Device Status
Information’.
