IEEE-488 Reference
5-34
3. Command path rules:
A. Each new program message must begin with the root command, unless it is
optional (e.g., [:SENSe]). If the root is optional, simply treat a command word
on the next level as the root.
B. The colon (:) at the beginning of a program message is optional and need not
be used. Example:
:stat:pres = stat:pres
C. When the path pointer detects a colon (:) it will move down to the next com-
mand level. An exception is when the path pointer detects a semicolon (;),
which is used to separate commands within the program message (see next
rule).
D. When the path pointer detects a colon (:) that immediately follows a semico-
lon (;), it resets back to the root level.
E. The path pointer can only move down. It cannot be moved up a level. Execut-
ing a command at a higher level requires that you start over at the root com-
mand.
4.
Using common commands and SCPI commands in same message:
Both com-
mon commands and SCPI commands can be used in the same message as long as
they are separated by semicolons (;). A common command can be executed at any
command level and will not affect the path pointer. Example:
:stat:oper:enab <NRf>; ptr <NRf>; *ESE <NRf>; ntr <NRf>
5.
Program Message Terminator (PMT):
Each program message must be terminat-
ed with an LF (line feed), EOI (end or identify) or an LF + EOI. The bus will hang
if your computer does not provide this termination. The following example shows
how a multiple command program message must be terminated:
:rout:open all;
scan (@1:5)
<PMT>
6. Command execution rules:
A. Commands are executed in the order that they are presented in the program
message.
B. An invalid command will generate an error and, of course, not be executed.
C. Valid commands that precede an invalid command in a multiple command
program message will be executed.
D. Valid commands that follow an invalid command in a multiple command pro-
gram message will be ignored. Example:
:rout:open all; harve; scan?
:open all will execute. Harve is an invalid command and will generate an error.
The scan query will be ignored.
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