R&S
®
CMW 500 Remote Control
Messages
Operating Manual 1202.3986.32 – 03 73
5.2.3 Device Messages (Commands and Device Responses)
Device messages are transferred via the USB interface, the LAN interface (VXI-11
protocol) or on the data lines of the GPIB bus, the "ATN" control line not being active.
The ASCII character set is used. A distinction is made according to the direction in
which device messages are transferred:
Commands
are messages the controller sends to the instrument. They operate the device
functions and request information.
Device responses
are messages the instrument sends to the controller after a query. They can
contain measurement results, instrument settings and information on the
instrument status.
Commands are subdivided according to two criteria:
1. According to the effect they have on the instrument:
Setting commands
cause instrument settings such as a reset of the instrument or setting the output
level to some value.
Queries
cause data to be provided for output on the GPIB bus, e.g. for identification of the
device or polling the active input.
2. According to their definition in standard IEEE 488.2:
Common commands
have a function and syntax that is exactly defined in standard IEEE 488.2. Typical
tasks are the management of the standardized status registers, reset and selftest.
Instrument-control commands
are functions that depend on the features of the instrument such as frequency
settings. A majority of these commands has also been standardized by the SCPI
consortium.
The device messages have a characteristic structure and syntax. In the SCPI
reference chapters all commands are listed and explained in detail.
5.2.4 SCPI Command Structure and Syntax
SCPI commands consist of a so-called header and, in most cases, one or more
parameters. The header and the parameters are separated by a "white space" (ASCII
code 0 to 9, 11 to 32 decimal, e.g. blank). The headers may consist of
several mnemonics which are separated by colons. Queries are formed by appending
a question mark to the header.
SCPI defines two command types with different syntax:
Common commands
Instrument-control commands
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