Stanford Research Systems SR780, Operating Manual And Programming Reference

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5-20 Remote Programming
SR780 Network Signal Analyzer
Command Format
Communications with the SR780 uses ASCII characters. Commands may be in either
UPPER or lower case. A command to the SR780 consists of a four character command
mnemonic with optional ?, arguments if necessary, and a command terminator. The
command, arguments and terminator may be separated by spaces. The terminator must be
a linefeed <lf> or carriage return <cr> on RS232, or a linefeed <lf> or EOI on GPIB. No
command processing occurs until a terminator is received. Commands function
identically on GPIB and RS232 whenever possible. Command mnemonics 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 (;).
There is no need to wait between commands. The SR780 has a 256 character input buffer
and processes commands in the order received. If the buffer fills up, the SR780 will hold
off handshaking on the GPIB and attempt to hold off handshaking on RS232. Similarly,
the SR780 has a 256 character output buffer to store output until the host computer is
ready to receive it. If either buffer overflows, both buffers are cleared and an error
reported.
The present value of a particular parameter may be determined by querying the SR780
for its value. A query is formed by appending a question mark ‘?’ to the command
mnemonic and omitting the desired parameter from the command. Values returned by the
SR780 are sent as a string of ASCII characters terminated by a carriage return <cr> on
RS232 and by a line-feed <lf> on GPIB. If multiple query commands are sent on one
command line (separated by semicolons, of course), the answers will be returned
individually, each with a terminator.
Examples of Commands
TSLP 0 <lf> Set the Trigger Slope to Positive
FCTR 1, 10E3 <lf> Set the Center Frequency of DisplayB to 10000 Hz (10 kHz)
FCTR ? 1 Query the Center Frequency of DisplayB
*IDN ? <lf> Query the Device Identification String
STRT <lf> Start the measurement (same as [Start/Reset] key)
Command Synchronization
IFC (Interface Ready, bit 7) in the Serial Poll status signals that the SR780 is ready to
receive and execute a command. When a command is received, this bit is cleared,
indicating that command execution is in progress. No other commands will be processed
until this command is completed. Commands received during this time are stored in the
buffer to be processed later. Only GPIB serial polling will generate a response while a
command is in progress. When all pending commands have executed, the IFC bit is set
again. By checking IFC with serial polls, a host computer can ensure that all previously
sent commands have finished before sending a new command.
Since most commands execute very quickly, the host computer does not need to
continually check the IFC bit. Commands may be sent one after another and they will be
processed immediately.