Including Common Commands; Using Queries; Types Of Scpi Messages - Agilent Technologies 66311A User Manual

The following message shows how to combine commands from different subsystems as well as within
the same subsystem:
VOLTage:LEVel 20;PROTection 28;:CURRent:LEVel 3;PROTection:STATe ON
Note the use of the optional header LEVel to maintain the correct path within the voltage and current
subsystems, and the use of the root specifier to move between subsystems.

Including Common Commands

You can combine common commands with system commands in the same message. Treat the common
command as a message unit by separating it with a semicolon (the message unit separator). Common
commands do not affect the header path; you may insert them anywhere in the message.
VOLTage:TRIGgered 17.5;:INITialize;*TRG
OUTPut OFF;*RCL 2;OUTPut ON

Using Queries

Observe the following precautions with queries:
♦ Set up the proper number of variables for the returned data.
♦ Read back all the results of a query before sending another command to the dc source. Otherwise a
Query Interrupted error will occur and the unreturned data will be lost.

Types of SCPI Messages

There are two types of SCPI messages, program and response.
♦ A program message consists of one or more properly formatted SCPI commands sent from the
controller to the dc source. The message, which may be sent at any time, requests the dc source to
perform some action.
♦ A response message consists of data in a specific SCPI format sent from the dc source to the
controller. The dc source sends the message only when commanded by a program message "query."
The following figure illustrates SCPI message structure:
Keywords
Keyword Separator
Message Unit
Data
;
VOLT : LEV 20 PROT 21
Message Unit Separators
Figure 6-2. Command Message Structure
Introduction to Programming - 6
Query Indicator
; : CURR?
<NL>
Message Terminator
Root Specifier
FIG2-1.GAL
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