Agilent X-Series Signal Generators SCPI Command Reference 7
SCPI Basics
SCPI Basics
Figure 1-2 Simplified Command Tree
The command closest to the top is the root command, or simply “the root.” Notice that you must
follow a particular path to reach lower level commands. In the following example, :POWer represents
AA, :ALC represents BB, :SOURce represents GG. The complete command path is
:POWer:ALC:SOURce? (:AA:BB:GG).
Paths Through the Command Tree
To access commands from different paths in the command tree, you must understand how the signal
generator interprets commands. The parser, a part of the signal generator firmware, decodes each
message sent to the signal generator. The parser breaks up the message into component commands
using a set of rules to determine the command tree path used. The parser keeps track of the current
path (the level in the command tree) and where it expects to find the next command statement. This
is important because the same keyword may appear in different paths. The particular path is
determined by the keyword(s) in the command statement.
A message terminator, such as a <new line> character, sets the current path to the root. Many
programming languages have output statements that automatically send message terminators.
NOTE The current path is set to the root after the line- power is cycled or when *RST is sent.
Command Parameters and Responses
SCPI defines different data formats for use in program and response messages. It does this to
accommodate the principle of forgiving listening and precise talking. For more information on
program data types refer to IEEE 488.2.
Forgiving listening means the command and parameter formats are flexible.
For example, with the :FREQuency:REFerence:STATe ON|OFF|1|0 command, the signal generator
accepts :FREQuency:REFerence:STATe ON, :FREQuency:REFerence:STATe 1, :FREQ:REF:STAT ON,
:FREQ:REF:STAT 1 to turn on the frequency reference mode.
Each parameter type has one or more corresponding response data types. A setting that you program
using a numeric parameter returns either real or integer response data when queried. Response data
(data returned to the controller) is more concise and restricted, and is called precise talking.
Precise talking means that the response format for a particular query is always the same.
For example, if you query the power state (:POWer:ALC:STATe?) when it is on, the response is
always 1, regardless of whether you previously sent :POWer:ALC:STATe 1 or :POWer:ALC:STATe ON.
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