Most controller programming languages
send these terminators automatically, but
allow changing it. So make sure the ter
-
minator is as above.
Example of a terminated program mes
-
sage:
program message unit terminator
program message unit
This program message consists of two
message units. The unit separator (semi
-
colon) separates message units.
Basically there are two types of com
-
mands:
Common Commands
The common command header starts with
the asterisk character (*), for example
*RST.
SCPI Commands
SCPI command headers may consist of
several keywords (mnemonics), separated
by the colon character (:).
Each keyword in a SCPI command
header represents a node in the SCPI
command tree. The leftmost keyword
(INPut in the previous example) is the
root level keyword, representing the
highest hierarchical level in the command
tree.
The keywords following represent
subnodes under the root node. See
‘COMMAND TREE’ on page 3-10 for
more details of this subject.
Forgiving Listening
The syntax specification of a command is
as follows:
ACQuisition:APERture8<numeric value>
Where: ACQ and APER specify the
shortform, and ACQuisition and APER
-
ture specify the longform. However,
ACQU or APERT are not allowed and
cause a command error.
In program messages either the long or
the shortform may be used in upper or
lower case letters. You may even mix up-
per and lower case. There is no semantic
difference between upper and lower case
in program messages. This instrument be-
havior is called forgiving listening.
For example, an application program may
send the following characters over the
bus:
SEND®
iNp:ImP81E6
The example shows the shortform used in
a mix of upper and lower case
SEND®
Input:Imp81E6
The example shows a mix of longform
and shortform and a mix of upper and
lower case.
3-8 Program and Response Messages
Introduction to SCPI
:INP:IMP 1E6;:ACQ:APER 0.1NL^END
R o o t
S u b n o d e s
E n d n o d e
Figure 3-7 The SCPI command tree.
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