Remote Control Basics
R&S
®
SMU200A
450Operating Manual 1007.9845.32 ─ 15
6.1.1 VISA Libraries
VISA is a standardized software interface library providing input and output functions to
communicate with instruments. The I/O channel (LAN or TCP/IP, USB, GPIB,...) is
selected at initialization time by means of the channel–specific address string ("VISA
resource string"), or by an appropriately defined VISA alias (short name). A VISA instal-
lation is a prerequisite for remote control using the following interfaces:
●
chapter 6.1.3.1, "VXI-11 Protocol", on page 452
●
chapter 6.1.4, "GPIB Interface (IEC/IEEE Bus Interface)", on page 453
For more information about VISA refer to the user documentation.
6.1.2 Messages
The messages transferred on the data lines of the GPIB bus or via the VXI-11 protocol
are divided into the following categories:
●
Interface messages
Interface messages are transmitted to the instrument on the data lines, with the
attention line being active (LOW). They are used to communicate between the con-
troller and the instrument. Interface messages can only be sent by instruments that
have GPIB bus functionality. For details see the sections for the required interface.
●
Instrument messages
Instrument messages are employed in the same way for all interfaces, if not indicated
otherwise in the description. Structure and syntax of the instrument messages are
described in chapter 6.3, "SCPI Command Structure", on page 468. A detailed
description of all messages available for the instrument is provided in the chapter
"Remote Control Commands".
There are different types of instrument messages, depending on the direction they
are sent:
- Commands
- Instrument responses
Commands
Commands (program messages) are messages the controller sends to the instrument.
They operate the instrument functions and request information. The commands are sub-
divided according to two criteria:
●
According to the effect they have on the instrument:
- Setting commands cause instrument settings such as a reset of the instrument
or setting the frequency.
- Queries cause data to be provided for remote control, e.g. for identification of the
instrument or polling a parameter value. Queries are formed by directly appending
a question mark to the command header.
●
According to their definition in standards:
- Common commands: their function and syntax are precisely defined in standard
IEEE 488.2. They are employed identically on all instruments (if implemented).
Remote Control Interfaces and Protocols
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