Agilent Technologies Agilent 86120C manual Program message terminator, Querying data

Programming

Reviewing SCPI Syntax Rules

Program message terminator

The string of instructions sent to the instrument are executed after the instruction terminator is received. The terminator may be either a new- line (NL) character, the End- Or- Identify (EOI) line asserted, or a combination of the two. All three ways are equivalent. Asserting the EOI sets the EOI control line low on the last byte of the data message. The NL character is an ASCII linefeed (decimal 10). The NL terminator has the same function as an EOS (End Of String) and EOT (End Of Text) terminator.

Querying data

Data is requested from the instrument using a query. Queries can be used to find out how the instrument is currently configured. They are also used to get results of measurements made by the instrument, with the query actually activating the measurement. String responses are returned as upper- case letters.

Queries usually take the form of a command followed by a question mark (?). After receiving a query, the instrument places the answer in its output queue. The answer remains in the output queue until it is read or another command is issued. For example, the query

OUTPUT 720;”:CALCULATE2:POINTS?”

places the number of points in the data set in the output queue. In HP BASIC, the controller input statement:

ENTER 720;Range

passes the value across the bus to the controller and places it in the variable Range. A newline character is appended to the response.

Sending another command or query before reading the result of a query causes the output queue to be cleared and the current response to be lost. This also generates an error in the error queue.

The output of the instrument may be numeric or character data depending on what is queried. Refer to the specific commands for the formats and types of data returned from queries.

You can send multiple queries to the instrument within a single pro- gram message, but you must also read them back within a single pro- gram message. This can be accomplished by either reading them back into a string variable or into multiple numeric variables. When you read the result of multiple queries into string variables, each response is separated by a semicolon.

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