Rohde & Schwarz SMBV100A, Руководство по эксплуатации

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Remote Control Basics
R&S
®
SMBV100A
492 Operating Manual 1176.8016.02 ─ 17
6.4 Command Sequence and Synchronization
IEEE 488.2 defines a distinction between overlapped and sequential commands:
●
A sequential command is one which finishes executing before the next command
starts executing. Commands that are processed quickly are implemented as
sequential commands. Sequential commands are not implemented in the instru-
ment, however the execution time of most commands is so short that they act as
sequential commands when sent in different command lines.
●
An overlapping command is one which does not automatically finish executing
before the next command starts executing. Usually, overlapping commands take
longer to process and allow the program to do other tasks while being executed. If
overlapping commands do have to be executed in a defined order, e.g. in order to
avoid wrong measurement results, they must be serviced sequentially. Keeping the
order is called synchronization between the controller and the instrument.
Setting commands within one command line, even though they can be implemented as
sequential commands, are not necessarily serviced in the order in which they have
been received. To make sure that commands are actually executed in a certain order,
each command must be sent in a separate command line.
Example: Commands and queries in one message
The response to a query combined in a program message with commands that affect
the queried value is not predictable.
The following commands always return the specified result:
:FREQ:STAR 1GHZ;SPAN 100 :FREQ:STAR?
Result:
1000000000
(1 GHz)
Whereas the result for the following commands is not specified by SCPI:
:FREQ:STAR 1GHz;STAR?;SPAN 1000000
The result could be the value of
STARt
before the command was sent since the instru-
ment can defer executing the individual commands until a program message termina-
tor is received. The result could also be 1 GHz if the instrument executes commands
as they are received.
As a general rule, send commands and queries in different program messages.
Command Sequence and Synchronization