User`s guide

Elan Digital Systems Ltd. 11 AD125 USER’S GUIDE
3.1.2 FIFO MODE
This is the mode intended for streaming data into the PC at high
speed.
Summary:
The AD125 takes continuous conversions in this mode. There is no
triggering. As soon as software sets RUN to on, the SRAM starts to
fill. The PC must empty the SRAM at a rate at least equal to the rate
at which it is being filled. An interrupt can be generated at 1/4 or
1/2 full to instruct the PC to fetch the correct amount of data from
the buffer. The throughput in this mode is PC speed dependent. If
an overrun occurs, i.e. the WRITE POINTER catches the READ
POINTER up, the AD125 will come out of RUN mode
automatically.
With well written Assembler/C software, 300KSPS should be
possible but the speed depends heavily on what happens to the data
once it is in the PC i.e. displayed / written to disk etc.
The “REP INSW” PC Assembler codes are essential to get high
speed.
3.1.3 SINGLE-SHOT MODE
This is the mode intended for streaming data into the PC at very low
rates.
Summary:
The AD125 takes single conversions in this mode. There is no
triggering. As soon as software sets RUN to on, a single conversion
occurs. The PC reads the sample out. The card automatically clears
the RUN state ready for the PC to set the next conversion in
progress. The time between conversions is totally controlled by the
PC. Remember to pre-clear the READ & WRITE POINTERS (and
do not try to set any pre-trigger) prior to commanding a single
conversion (this ensures that the process stops immediately after one
conversion rather than filling the whole SRAM buffer).