Stanford Research Systems DS345, Manual

Page: 52 / 139

Programming Commands
3-2
There is no need to wait between commands. The DS345 has a 256 charac-
ter input buffer and processes commands in the order received. If the buffer
fills up the DS345 will hold off handshaking on the GPIB and attempt to hold
off handshaking on RS232. If the buffer overflows the buffer will be cleared
and an error reported. Similarly, the DS345 has a 256 character output buf-
fer to store output until the host computer is ready to receive it. If the output
buffer fills up it is cleared and an error reported. The GPIB output buffer
may be cleared by using the Device Clear universal command.
The present value of a particular parameter may be determined by querying
the DS345 for its value. A query is formed by appending a question mark "?"
to the command mnemonic and omitting the desired parameter from the
command. If multiple queries are sent on one command line (separated by
semicolons, of course) the answers will be returned in a single response line
with the individual responses separated by semicolons. The default re-
sponse terminator that the DS345 sends with any answer to a query is car-
riage return-linefeed <cr><lf> on RS232, and linefeed plus EOI on GPIB. All
commands return integer results except as noted in individual command de-
scriptions.
Examples of Command Formats
MRKF1, 1000.0 <lf> Sets the stop marker to 1000 Hz (2 parame-
ters).
MRKF? 1 <lf> Queries the stop marker frequency (query of 2
parameter command ).
. *IDN? <lf> Queries the device identification (query, no pa-
rameters).
*TRG <lf> Triggers a sweep (no parameters).
FUNC 1 ;FUNC? <lf> Sets function to square wave(1) then queries
the function.
Programming Errors
The DS345 reports two types of errors that may occur during command exe-
cution: command errors and execution errors. For example, unrecognized
commands, illegal queries, lack of terminators, and non-numeric arguments
are examples of command errors. Execution errors are errors that occur dur-
ing the execution of syntactically correct commands. For example, out of
range parameters and commands that are illegal for a particular mode of op-
eration are classified as execution errors
.
No Command Bit
The NO COMMAND bit in the serial poll register indicates that there no com-
mands waiting to be executed in the input queue. This bit is reset when a
complete command is received in the input queue and is set when all of the
commands in the queue have been executed. This bit is useful in determin-
ing when all of the commands sent to the DS345 have been executed. This
is convenient because some commands, such as setting the function, modu-
lation, or autocalibration, take a long time to execute and there is no other
way of determining when they are done. The NO COMMAND bit may be
read while commands are being executed by doing a GPIB serial poll. There
is no way to read this bit over RS232. Note that using the *STB? query to
read this bit will always return the value 0 because it will always return an an-
swer while a command is executing- the *STB? command itself!