Interface - Stanford Research Systems SR810 Manual

Remote Programming
returned by the SPTS? query), then an error occurs. Remember, SPTS?
returns N where N is the total number of bins - the TRCB? command
numbers the bins from 0 (oldest) to N-1 (most recent). If data storage is
set to Loop mode, make sure that storage is paused before reading any
data. This is because the points are indexed relative to the most recent
point which is continually changing.
FAST (?) {i}
The FAST command sets the fast data transfer mode on and off. The
parameter i selects:
i=0: Off
i=1: On (DOS programs or other dedicated data collection computers)
i=2: On (Windows Operating System Programs)
When the fast transfer mode is on, whenever data is sampled (during a
scan), the values of X and Y are automatically transmitted over the GPIB
interface (this mode is not available over RS-232). The sample rate sets
the frequency of the data transfers. It is important that the receiving
interface be able to keep up with the transfers.
To use the FAST2 mode, a ROM version of 1.06 or higher is required in
the SR810. If you need a ROM upgrade, please contact Stanford
Research Systems. The FAST2 version uses the lock-in transmit queue
to buffer the GPIB data being sent to the host. Since the transmit queue
can buffer a maximum of 63 X and Y data pairs, the host can only be
diverted for short periods of time (e.g. 120mS at 512Hz sample rate)
without causing the lock-in to "time out" and abort the FAST mode data
transfer.
The values of X and Y are transferred as signed integers, 2 bytes long
(16 bits). X is sent first followed by Y for a total of 4 bytes per sample.
The values range from -32768 to 32767. The value ±30000 represents
±full scale (i.e. the sensitivity).
Offsets and expands are included in the values of X and Y. The
transferred values are (raw data - offset) x expand. The resulting value
must still be a 16 bit integer. The value ±30000 now represents ±full
scale divided by the expand factor.
At fast sample rates, it is important that the receiving interface be able to
keep up. If the SR810 finds that the interface is not ready to receive a
point, then the fast transfer mode is turned off.
The fast transfer mode may be turned off with the FAST0 command.
The transfer mode should be turned on (using FAST1 or FAST 2) before
a scan is started. Then use the STRD command (see below) to start a
scan. After sending the STRD command, immediately make the SR810
a talker and the controlling interface a listener. Remember, the first
transfer will occur with the very first point in the scan. If the scan is
started from the front panel or from the trigger input, then make sure that
the SR810 is a talker and the controlling interface a listener BEFORE the
scan actually starts.
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