For example,
:SYSTe:PRESe
is illegal and will generate an error. The com-
mand will not be executed.
Query
Observe the following precautions with queries:
•
Set up the proper number of variables for the returned data. For example, if
you are reading back a measurement array, you must dimension the array
according to the number of measurements that you have placed in the
measurement buffer.
•
Read back all the results of a query before sending another command to the
instrument. Otherwise a Query Interrupted error will occur and the unre-
turned data will be lost.
1.3 Message Type of SCPI
There are two types of SCPI messages, program and response.
•
Program message: A program message consists of one or more properly
formatted SCPI commands sent from the controller to the instrument. The
message, which may be sent at any time, requests the instrument to perform
some action.
•
Response message: A response message consists of data in a specific
SCPI format sent from the instrument to the controller. The instrument sends
the message only when commanded by a program message called a
"query."
The next figure illustrates SCPI message structure:
The message unit
The simplest SCPI command is a single message unit consisting of a command
header (or keyword) followed by a message terminator. The message unit may
include a parameter after the header. The parameter can be numeric or a string.
Copyright © Itech Electronic Co., Ltd.
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