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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.
The basic parts of the message in Figure 6-1 are:
Message Component
Headers
Header Separator
Data
Data Separator
Message Units
Message Unit Separator
Root Specifier
Query Indicator
Message Terminator
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
Figure 6-2. Command Message Structure
VOLT LEV PROT CURR
The colon in VOLT:LEV
4.5 4.8
The space in VOLT 4. 5 and PROT 4. 8
VOLT:LEV 4.5
PROT 4.8 CURR?
The semicolons in VOLT: LEV 4. 5; and PROT 4. 8;
The colon in PROT 4. 8; : CURR?
The question mark in CURR?
The <NL> (newline) indicator. Terminators are not part of the SCPI syntax.
Example
Remote Programming
49
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