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 key words. Queries are formed by directly appending a question mark to the header.
Common commands and device-specific commands differ in their syntax.
The analyzers are compatible to the final SCPI version 1999.0. Not all of the commands supported by the instrument are taken from the SCPI standard (Standard Commands for Programmable Instruments), however, their syntax follows SCPI rules. The SCPI standard is based on standard IEEE 488.2 and aims at the standardization of instrument-control commands, error handling and the status registers.
The requirements that the SCPI standard places on command syntax, error handling and configuration of the status registers are explained in detail in the following sections.
In contrast to instruments with manual control, which are designed for maximum possible operating convenience, the priority of remote control is the "predictability" of the device status. This means that when incompatible settings are attempted, the command is ignored and the device status remains unchanged, i.e. other settings are not automatically adapted. Therefore, GPIB bus control programs should always define an initial device status (e.g. with the command *RST) and then implement the required settings.
Common (=device-independent) commands consist of a header preceded by an asterisk "*" and possibly one or more parameters.
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Examples: |
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*RST |
RESET, resets the instrument. |
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*ESE 253 |
EVENT STATUS ENABLE, sets the bits of the event status enable registers. |
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*ESR? |
EVENT STATUS QUERY, queries the contents of the event status register. |
Instrument-control commands are based on a hierarchical structure and can be represented in a command tree. The command headers are built with one or several mnemonics (keywords). The first level (root level) mnemonic identifies a complete command system.
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Example: For commands of lower levels, the complete path has to be specified, starting on the left with the highest level, the individual key words being separated by a colon ":". |
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Example: This command is located on the third level of the SENSe system. It defines the start frequency of the sweep. |
The following rules simplify and abbreviate the command syntax:
Some mnemonics occur on several levels within one command system. Their effect depends on the structure of the command, i. e. on the position in the command header they are inserted in.
Example:
SOURce:FREQuency:CW lGHZ
This command contains the key word SOURce in the first command level. It defines the frequency for sweep types operating at fixed frequency.
TRIGger:SOURce EXTernal
This command contains the key word SOURce in the second command level. It defines the trigger source “external trigger”.
Some command systems permit certain mnemonics to be optionally inserted into the header or omitted. These mnemonics are marked by square brackets in this manual. The full command length must be recognized by the instrument for reasons of compatibility with the SCPI standard. Some commands are considerably shortened by omitting optional mnemonics.
Example:
TRIGger[:SEQuence]:SOURce EXTernal
This command defines the trigger source “external trigger”. The following command has the same effect:
TRIGger:SOURce EXTernal
An optional mnemonic must
not be omitted if its effect is additionally specified by a numeric suffix.
The key words feature a long form and a short form. Either the short form or the long form can be entered; other abbreviations are not permitted.
Example:
TRIGger:SOURce EXTernal
TRIG:SOUR EXT
The short form is marked
by upper case letters, the long form corresponds to the complete word.
Upper case and lower case notation only serves to distinguish the two
forms in the manual, the instrument itself is case-insensitive.
Parameters must be separated from the header by a "white space". If several parameters are specified in a command, they are separated by a comma ",". For a description of the parameter types, refer to section Parameters.
Example:
SOURce:GROup 1,1
This command defines a group of measured ports.
If a device features several functions or features of the same kind, e.g. several channels or test ports, the desired function can be selected by a suffix added to the command. Entries without suffix are interpreted like entries with the suffix 1.
Example:
SOURce:GROup2 1,1
This command defines a second group (group no 2) of measured ports.
A command line may consist of one or several commands. It is terminated by a <New Line>, a <New Line> with EOI or an EOI together with the last data byte. Visual BASIC automatically produces an EOI together with the last data byte.
Several commands in a command line must be separated by a semicolon ";". If the next command belongs to a different command system, the semicolon is followed by a colon.
Example: CALL IBWRT(device%, "TRIGger:SOURce EXTernal;:SENSe:FREQuency:STARt 1GHZ")
This command line contains two commands. The first command belongs to the TRIGger system and defines the trigger source (external trigger). The second command belongs to the SENSe system and defines the start frequency of the sweep.
If the successive commands belong to the same system, having one or several levels in common, the command line can be abbreviated. To this end, the second command after the semicolon starts with the level that lies below the common levels. The colon following the semicolon must be omitted in this case.
Example: CALL IBWRT(device%, "TRIG:SOUR EXT;:TRIG:TIM 0.1")
This command line is represented in its full length and contains two commands separated from each other by the semicolon. Both commands are part of the TRIGger command system, i.e. they have one level in common.
When abbreviating the command line, the second command begins with the level below TRIG. The colon after the semicolon is omitted. The abbreviated form of the command line reads as follows:
CALL IBWRT(device%, "TRIG:SOUR EXT; TIM 0.1")
However, a new command line always begins with the complete path.
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Example: |
CALL IBWRT(device%,
"TRIG:SOUR
EXT ") |
A query is defined for each setting command unless explicitly specified otherwise. It is formed by adding a question mark to the associated setting command. According to SCPI, the responses to queries are partly subject to stricter rules than in standard IEEE 488.2.
1. The requested parameter is transmitted without header.
Example: TRIGger:SOURce?
Response: IMM
2. Maximum
values, minimum values and all further quantities which are requested
via a special text parameter are returned as numerical values.
Example: SENSe:FREQuency:STOP?
MAX Response:
8000000000
3. Numerical values are output without their unit.
The default unit for each command is reported in the SCPI
command description.
Example: SENSe:FREQuency:STOP?
MAX Response:
8000000000 for 8
GHz
4. Boolean values are returned as 0 (for OFF)
and 1 (for ON).
Example: SWEep:TIME:AUTO? Response: 1
5. Text (character data) is returned in short form
(see also next section).
Example: TRIGger:SOURce?
Response: IMM
