The
SCPl
command
The
HP
E1440A
firmware contains a piece of software, called the
parser
SCPI command parser, which is responsible for decoding the program
strings entering the instrument. For efficient programming of the
instrument, it is helpful to understand how this parser operates.
Definition of terms
Before explaining the parser operation, we should explain some of the
terms used in the text.
Common commands
/
SCPI commands
There are two command types understood by the
E1440,
common
commands and SCPI commands.
w
Common commands all begin with an asterisk
('*').
They are
organized in a non-hierarchical ('flat') manner.
A
common command is allowed where a program message unit (see
below) is allowed.
Common commands do not affect the current base node (see
below).
w
SCPI commands are all those commands that do not begin with an
asterisk. They are organized hierarchically.
Program message
A
program message consists of one or more program message units
(see below) separated by program message unit separators (semicolon
-
(';') and terminated by a program message terminator (carriage
return
-
line feed (abbreviated as
<CR/LF>)
sequence).
An example for a program message
is
:
':VOLT:OFFS
1
V
;
:FREQ
5
kHz <CR/LF>'
Note
As
you see, the final
';'
(which should be between
'
. . .
kHz' and
3
'<CR/LF7)
can be omitted.
This program message actually consists of two program message
units:
':VOLT:OFFS
1
V' and ':FREQ
5
kHz'
Program message unit (command)
A
program message unit is what we commonly call a command. The
term 'command' is used below, because it sounds more familiar and
is not as typing-intensive as 'program message unit7.
A
command consists of one or more command nodes (see below)
separated by colons
0:').
The first command node might be
prepended by a colon as well, but that has a special effect.
If
a
command has a parameter, then the parameter must be separated
by at least one space character (no tab) from the end node (see
--
5-2
Command Reference
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