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Protocol Exceptions
If an error occurs during the information exchange, the exchange may not be
completed in a normal manner. Some of the protocol exceptions are shown
below.
Command Error A command error will be reported if the instrument
detects a syntax error or an unrecognized command header.
Execution Error An execution error will be reported if a parameter is
found to be out of range, or if the current settings do not allow execution
of a requested command or query.
Device-specific Error A device-specific error will be reported if the
instrument is unable to execute a command for a strictly device
dependent reason.
Query Error A query error will be reported if the proper protocol for
reading a query is not followed. This includes the interrupted and
unterminated conditions described in the following paragraphs.
Syntax Diagrams
The example syntax diagram is in this chapter are similar to the syntax
diagrams in the IEEE 488.2 specification. Commands and queries are sent to
the instrument as a sequence of data bytes. The allowable byte sequence for
each functional element is defined by the syntax diagram that is shown.
The allowable byte sequence can be determined by following a path in the
syntax diagram. The proper path through the syntax diagram is any path
that follows the direction of the arrows. If there is a path around an element,
that element is optional. If there is a path from right to left around one or
more elements, that element or those elements may be repeated as many
times as desired.
Message Communication and System Functions
Syntax Diagrams
5–5