Keysight E4356A, Operating Manual

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Remote Programming 49
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
power supply. The message, which may be sent at any time, requests the power supply to perform some action.
 A
response message
consists of data in a specific SCPI format sent from the power supply to the controller. The
power supply sends the message only when commanded by a special program message called a "query."
Structure of a SCPI Message
SCPI messages consist of one or more message units ending in a message terminator. The terminator is not part of the
syntax, but implicit in the way your programming language indicates the end of a line (such as a newline or end-of-line
character).
The following command message (see Figure 6-2) is briefly described here, with more details in subsequent paragraphs.
Figure 6-2. Command Message Structure
The basic parts of the message in Figure 6-1 are:
Message Component Example
Headers
VOLT LEV PROT CURR
Header Separator
The
colon
in
VOLT:LEV
Data
4.5 4.8
Data Separator
The space in
VOLT 4. 5
and
PROT 4. 8
Message Units
VOLT:LEV 4.5 PROT 4.8 CURR?
Message Unit Separator
The
semicolons
in
VOLT: LEV 4. 5
;
and
PROT 4. 8;
Root Specifier
The
colon
in
PROT 4. 8; : CURR?
Query
Indicator
The
question mark
in
CURR?
Message Terminator
The <
NL
> (newline) indicator. Terminators are not part of the SCPI syntax.
The Message Unit.
The simplest SCPI command is a single message unit consisting of a command header (or keyword)
followed by a message terminator.
ABOR
VOLT?
The message unit may include a parameter after the header. The parameter usually is numeric, but it can be a string:
VOLT 20
VOLT MAX
Headers.
Headers (which are sometimes known as "keywords") are instructions recognized by the power supply interface.
Headers may be either in the long form or the short form.