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SCPI Introduction

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.

ITech IT8000 Series Programming Guide

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