Stanford Research Systems SR830 Manual page 101

Remote Programming
FAST (?) {i}
STRD
always be ready to receive the next byte. In general, using binary trans-
fers on the RS232 interface is not recommended.
The parameter i selects the display buffer (i=1, 2) and is required. Points
are read from the buffer starting at bin j (j≥0). A total of k bins are read
(k≥1) for a total transfer of 4k bytes. To read a single point, set k=1. Both
j and k are required. If j+k exceeds the number of stored points (as
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.
The FAST command sets the fast data transfer mode on and off. The
parameter i selects On (i=1) or Off (i=0). When the fast transfer mode is
on, whenever data is sampled and stored, the values of X and Y are
automatically transmitted over the GPIB interface (this mode is not avail-
able over RS232). The sample rate sets the frequency of the data trans-
fers. It is important that the receiving interface be able to keep up with
the transfers. FAST only sends data when data is being stored. If the
storage buffer is single-shot and full, then no data will be transferred.
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 trans-
ferred 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 SR830 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.
Make sure that the SR830 transmit buffer is empty by doing a dummy
query before a FAST transfer (for example, send SPTS? and read the
answer and ignore it). The transfer mode should be turned on (using
FAST1) before storage is started. Then use the STRD command (see
below) to start data storage. After sending the STRD command, immedi-
ately make the SR830 a talker and the controlling interface a listener.
Remember, the first transfer will occur with the very first point.
After using FAST1 to turn on fast data transfer, use the STRD command
to start the data storage. STRD starts data storage after a delay of 0.5
sec. This delay allows the controlling interface to place itself in the read
mode before the first data points are transmitted. Do not use the STRT
command to start the scan. See the programming examples at the end
of this section.
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