Agilent Technologies 6812B Introduction to Scpi, Conventions Used in This Guide, Computer font

Introduction to Programming - 2

Introduction to SCPI

SCPI (Standard Commands for Programmable Instruments) is a programming language for controlling instrument functions over the GPIB. SCPI is layered on top of the hardware-portion of IEEE 488.2. The same SCPI commands and parameters control the same functions in different classes of instruments. For example, you would use the same DISPlay command to control the ac source display and the display of a SCPI-compatible multimeter.

Conventions Used in This Guide

Angle brackets		<	>	Items within angle brackets are parameter abbreviations. For example,
				<NR1> indicates a specific form of numerical data.
Vertical bar				Vertical bars separate alternative parameters. For example, NORM TEXT
				indicates that either "TEXT" or "NORM" can be used as a parameter.
Square Brackets		[	]	Items within square brackets are optional. The representation
				[SOURce:]LIST means that SOURce: may be omitted.
Braces {	}			Braces indicate parameters that may be repeated zero or more times. It is
				used especially for showing arrays. The notation <A>{<,B>} shows that
				parameter "A" must be entered, while parameter "B" may be omitted or
				may be entered one or more times.
Computer font				Computer font is used to show program lines in text. TRIGger:DELay .5
				shows a program line.

Types of SCPI Commands

SCPI has two types of commands, common and subsystem.

υCommon commands generally are not related to specific operation but to controlling overall ac source functions, such as reset, status, and synchronization. All common commands consist of a three-letter mnemonic preceded by an asterisk:*RST*IDN?*SRE 8

υSubsystem commands perform specific ac source functions. They are organized into an inverted tree structure with the "root" at the top. Some are single commands while others are grouped within specific subsystems.

Refer to appendix A for the ac source SCPI tree structure.

Types of SCPI Messages

There are two types of SCPI messages, program and response.

υA program message consists of one or more properly formatted SCPI commands sent from the controller to the ac source. The message, which may be sent at any time, requests the ac source to perform some action.

υA response message consists of data in a specific SCPI format sent from the ac source to the controller. The ac source sends the message only when commanded by a program message called a "query."

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