SRS Labs manual SR530 Guide to Programming, Communicating with the SR530, Command Syntax

SR530 Guide to

Programming

The SR530 Lock-in Amplifier is remotely programmable via both RS232 and GPIB interfaces. It may be used with laboratory computers or simply with a terminal. All front panel features (except signal input selection and power) may be controlled and read via the computer interfaces. The SR530 can also read the analog outputs of other laboratory instruments using its four general purpose analog input ports. There are also two programmable analog output ports available to provide general purpose control voltages.

Communicating with the SR530

Before using either the RS232 or GPIB interface, the appropriate configuration switches need to be set. There are two banks of 8 switches, SW1 and SW2, located on the rear panel. SW1 sets the GPIB address and SW2 sets the RS232 parameters. The configuration switches are read continuously and any changes will be effective immediately. For details on switch settings, see page 7 at the front of this manual.

Command Syntax

Communications with the SR530 use ASCII characters. Commands to the SR530 may be in either UPPER or lower case.

A command to the SR530 consists of one or two command letters, arguments or parameters if necessary, and an ASCII carriage return (<cr>) or line-feed (<lf>) or both. The different parts of the command do not need to be separated by spaces. If spaces are included, they will be ignored. If more than one parameter is required by a command, the parameters must be separated by a comma. Examples of commands are:

G 5 <cr>	set the sensitivity to 200 nV
T 1,4 <cr>	set the pre filter to 30 mS
F <cr>	read the reference frequency
P 45.10 <cr>		set phase shift to 45.10¡
X 5,-1.23E-1 <cr>		set port X5 to -0.123 V

Multiple commands may be sent on a single line. The commands must be separated by a semicolon

(;)character. The commands will not be executed until the terminating carriage return is sent.

An example of a multiple command is:

G 5; T 1,4; P 45.10 <cr>

It is not necessary to wait between commands. The SR530 has a command input buffer of 256 characters and processes the commands in the order received. Likewise, the SR530 has an output buffer (for each interface) of 256 characters.

In general, if a command is sent without parameters, it is interpreted as a request to read the status of the associated function or setting. Values returned by the SR530 are sent as a string of ASCII characters terminated usually by carriage return, line-feed. For example, after the above command is sent, the following read commands would generate the responses shown below.

Command	Response from the SR530
G <cr>	5<cr><lf>
T 1 <cr>	4<cr><lf>
P <cr>	45.10<cr><lf>

The choice of terminating characters sent by the SR530 is determined by which interface is being used and whether the 'echo' feature is in use. The terminating sequence for the GPIB interface is always <cr><lf> (with EOI). The default sequence for RS232 is <cr> when the echo mode is off, and <cr><lf> when the echo mode is on. The terminating sequence for the RS232 interface may be changed using the J command.

Note that the terminating characters are sent with each value returned by the SR530. Thus, the response to the command string G;T1;P<cr> while using the RS232 non-echo mode would be 5<cr>4<cr>45.10<cr>.

Front Panel Status LED's

The ACT LED flashes whenever the SR530 is sending or receiving characters over the computer interfaces.

The ERR LED flashes whenever an error has occurred, such as, an illegal command has been received, a parameter is out of range, or a communication buffer has exceeded 240 characters. This LED flashes for about three seconds on power-up if the battery voltage is insufficient to retain previous instrument settings.

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