REMOTE PROGRAMMING
4-2
Similarly, the SR715/720 has a 256 character
output buffer 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 SR715/720 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 response terminator that the
SR715/720 sends with any answer to a query is
carriage return-linefeed <cr><lf> on RS232 and
linefeed plus EOI on GPIB, except for binary
answers which are terminated by a single <lf> on
both interfaces. All commands return integer
results except as noted in individual command
descriptions.
Examples of Command Formats
FREQ 2 <lf>
Sets the drive frequency
to 1000 Hz ( 1 parameter).
FREQ?
<lf>
Queries the drive
frequency (query of 1
parameter command ).
BLIM 0,3,1000<lf>
Sets the upper limit of bin
3 to 1000W (3
parameters).
BLIM? 0,3<lf>
Queries the upper limit of
bin 3 (query of 3
parameter command).
*
IDN?
<lf>
Queries the device
identification (query, no
parameters).
*
TRG <lf>
Triggers a measurement
(no parameters).
FREQ 1 ;FREQ? <lf>
Sets frequency to 120Hz
(1) then queries the
frequency.
PROGRAMMING ERRORS
The SR715/720 reports two types of errors that
may occur during command execution: command
errors and execution errors. Command errors are
errors in the command syntax. For example,
unrecognized commands, illegal queries, lack of
terminators, and non-numeric arguments are
examples of command errors. Execution errors
are errors that occur during the execution of
syntactically correct commands. For example, out
of range parameters and commands that are
illegal for a particular mode of operation are
classified as execution errors.
NO COMMAND BIT
The NO COMMAND bit is a bit in the serial poll
register that indicates that there no commands
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 determining when all of the
commands sent to the SR715/720 have been
executed. This is convenient because some
commands, such as taking a measurement, 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 answer while a command is
executing- the
*
STB? command itself!
