PEL-60-60-10 - Physical Instruments

OVER VIEW SCPI LANGUAGE
The SCPI language uses a hierarchical structure in its programming syntax similar to an inverted tree. The
command is organized with root level commands positioned at the top, with multiple sub commands below
each root-level command. For example, VOLTage, which is a branch of SOURce, is a command mnemonic
and it forms a subtree of its own. VOLTage has three sub-level commands: LEVel, SLEW, TLEVel. At the
end of a sub-level command, you can attach a parameter, a question mark (for query), a colon (command
mnemonics separator), a semicolon (for multiple commands in a message) or an end of line terminator. To
execute a sub-level command, you must specify the complete path from root-level. Each command statement
is simply I/O ASCII data strings incorporated within high-level programming language (GW-BASIC, HP
BASIC, Quick Basic, Pascal, etc.).
Command Mnemonics
Data
Message Terminator
Query Indicator
VOLT:LEV 10;TLEV 15;:RES:TLEV?
Command Statement
Root Specifier
Command Statement Separator
Command Message
Syntax Overview
Use of the Colon (:)
A colon is used to separate command mnemonics. It indicates a move down in branch level of the
command tree. The command follows a colon is a sub command of the command immediate before the
colon. When colon precedes the first command mnemonic of a message unit, it becomes root specifier.
Its action places the parser (decoder) at the root of the command tree. Parser can only travel downward
the command tree. If another command at different branch needs to be executed, a root specifier (colon)
is required to place parser at origin and a complete path from root level should also be defined.
Use of the Semicolon (;)
A semicolon is used to separate two command statements with the same command message string. The
semicolon does not change location of the parser in the command tree. Only command statements that
are in the current path of the first command statement can be combined to form a command message.
Use of the Space ( )
A white space is used to separate a parameter (data) from a command mnemonic. When a command
statement includes parameter, data always follows the last keyword of a command.
Use of the Comma (,)
A comma is used to separate adjacent parameters if a command requires more than one parameter.
Use of the Query (?)
A query command is used to instruct the instrument to send a response message. Queries return either
measured values or internal instrument setting. When a keyword is followed by a question mark, it
becomes a query. The ? follows the last keyword of a command statement. You should read back the
result of first query before you send out another query or command. Otherwise, returned data will be
lost.
Common Commands:
Commands starting with a * and three-letter mnemonic are called common commands. They are
generally not related to specific device operation but to perform the identical function for all instruments
that are compliant with the IEEE-488.2 interface standard. Common commands can be mixed in with
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