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Boonton 4540 Series RF Power Meter

Remote Operation

5-3

5.4.5 Command Arguments and Queries

Many commands require arguments. In this case, the entire command string is sent, followed by the argument. A space is

used to separate the command from the argument. For example, ―SENSe:CORRection:DCYCle 25.0

‖

sets duty cycle

correction to a value of 25.0. Arguments may be numeric, or alphanumeric. If a command requires more than one numeric

argument, the arguments must be sent as a comma delimited list.
To read the current value of a particular parameter, the Query Form of its command may be used. A command query is

formed by appending a question-mark (―?

‖)

suffix to the command instead of an argument list. There should not be any

whitespace between the command and the suffix. For example, ―SENSe:CORRection:DCYCle?

‖

queries the duty cycle

correction parameter, and causes the instrument to return its current value.

5.4.6 Semicolon Command Separators

The semicolon (―

;‖)

character is used to separate multiple commands on a single line. However, the parsing path is affected

when more than one command is combined on a line. As noted previously, the first command of a line is always referenced

to the root level whether or not the command is prefixed by a colon. However, for the second and succeeding commands, the

parsing level is NOT reset to the root level, but rather referenced from the current node. This allows the parser to remain at

the current node, and execute other commands from that node without resending the entire node string. For example, the

following multi-command strings are equivalent:
:SENSe:CORRection:DCYCle 25.0; :SENSe:CORRection:CALFactor 2.12;

(two full-path commands)

:SENSe:CORRection:DCYCle 25.0; CALFactor 2.12;

( second command referenced to CORRection node)

SENSe:CORRection:DCYCle 25.0; CALFactor 2.12;

(leading colon omitted from first command)

If a command does not belong to the same subsystem as the preceding command on the same line, then its full path must be

specified, including the colon prefix.

5.4.7 Command Terminators

All SCPI command strings transmitted to the instrument must be terminated. For commands sent via the GPIB bus, any

character with the IEEE488 EOI (End-Or-Identify) control line asserted may be used as a terminator. This may be the last

letter of the command, query or argument. Optionally, a CR (ASCII 13) and/or LF (ASCII 10) may be included. These are

ignored by the parser, but if present, the EOI must be asserted on the last message character transmitted.
On USB and LAN messages, the packetized protocols provide automatic termination of each message. Again, CR and/or LF

may be present, but must be the last message character(s) of the packet.
When the terminating condition is met (end of GPIB message or end of USB or LAN packet), the SCPI path is first reset to

the root level, and the received message is then passed to the SCPI parser for evaluation.

5.4.8 4540 Series SCPI Implementation

The SCPI Model of the 4540 provides a single or dual SENSe sub-system to handle sensor input and a matching single or

dual CALCulate sub-system to process the data obtained from the sensors into useful results. A TRIGger sub-system

provides for measurement and signal synchronization. DISPlay commands are used for graph and text display control,

formatting and timebase selection. The CALibration sub-system is used to calibrate power sensors. Channel dependent

commands end with a number to indicate the desired channel as follows:
Examples:

:CALCulate:STATe ON

Turn on measurement channel 1 (default channel number)

:CALCulate1:STATe ON

Turn on measurement channel 1 (specified channel number)

:CALC:STAT ON