SRS Labs SR850 manual Remote Programming

REMOTE PROGRAMMING

INTRODUCTION

The SR850 DSP Lock-in Amplifier may be remote- ly programmed via either the RS232 or GPIB (IEEE-488) interfaces. Any computer supporting one of these interfaces may be used to program the SR850. Both interfaces are receiving at all times, however, the SR850 will send responses only to the interface specified in the System Setup menu (Output To RS232/GPIB function).

Use the OUTX command at the beginning of every program to direct the responses to the correct interface. All front panel features (except power) may be controlled.

COMMUNICATING WITH GPIB

The SR850 supports the IEEE-488.1 (1978) inter- face standard. It also supports the required common commands of the IEEE-488.2 (1987) standard. Before attempting to communicate with the SR850 over the GPIB interface, the SR850's device address must be set. The address is set in the Setup GPIB menu and may be set between 0 and 30.

COMMUNICATING WITH RS232

The SR850 is configured as a DCE ( transmit on pin 3, receive on pin 2) device and supports CTS/ DTR hardware handshaking. The CTS signal (pin

5)is an output indicating that the SR850 is ready, while the DTR signal (pin 20) is an input that is used to control the SR850's data transmission. If desired, the handshake pins may be ignored and a simple 3 wire interface (pins 2,3 and 7) may be used. The RS232 interface baud rate, number of data bits, and parity must be set. These are set in the Setup RS232 menu.

STATUS INDICATORS AND QUEUES

To assist in programming, the SR850 has 5 inter- face status indicators which are displayed at the bottom of the screen. The RS232/GPIB Activity indicator flashes whenever a character is received or transmitted over either interface. The ERR indi- cator flashes when an error, such as an illegal command, or parameter out of range, has been detected. The REM indicator is on whenever the

SR850 is in a remote state (front panel locked out). The LOC indicator is on when the front panel is active (Local Mode). The SRQ indicator is on when the SR850 generates a service request. SRQ stays on until a serial poll is completed.

To help find program errors, the SR850 can dis- play the interface buffers on the screen. This screen is activated by the View Queue function in the Setup Communications menu. The last 256 characters received and transmitted by the SR850 are displayed.

COMMAND SYNTAX

Communications with the SR850 uses ASCII char- acters. Commands may be in either UPPER or lower case and may contain any number of embedded space characters. A command to the SR850 consists of a four character command mnemonic, arguments if necessary, and a com- mand terminator. The terminator must be a line- feed <lf> or carriage return <cr> on RS232, or a linefeed <lf> or EOI on GPIB. No command pro- cessing occurs until a command terminator is received. Commands function identically on GPIB and RS232 whenever possible. Command mne- monics beginning with an asterisk "❊" are IEEE-

488.2(1987) defined common commands. These commands also function identically on RS232. Commands may require one or more parameters. Multiple parameters are separated by commas (,).

Multiple commands may be sent on one command line by separating them with semicolons (;). The difference between sending several commands on the same line and sending several independent commands is that when a command line is parsed and executed, the entire line is executed before any other device action proceeds.

There is no need to wait between commands. The SR850 has a 256 character input buffer and pro- cesses commands in the order received. If the buffer fills up, the SR850 will hold off handshaking on the GPIB and attempt to hold off handshaking on RS232. Similarly, the SR850 has a 256 charac- ter output buffer to store outputs until the host

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