User`s guide

Elan Digital Systems Ltd. 10 AD125 USER’S GUIDE
3. CONTROLLING THE AD125
3.1 ACQUISITION MODES
In all modes, the AD125 performs its conversions in around 2.0µs
(1.66µs for the AD1x6). The conversion rate is software
programmable and is achieved by “spreading-out” the conversions
using the PACER clock.
3.1.1 BURST MODE
This is the mode intended for transient capture or vibration analysis.
Summary:
The AD125 is set up with trigger threshold and edge. The READ
and WRITE POINTERS are put into a known starting state. The
pre-trigger depth is configured. The system is set into RUN mode
but with trigger disabled. The AD125 starts taking samples. After
some elapsed time, software sets ENTRIG to on to “arm” the system.
The AD125 will then wait until the incoming sample data meets the
trigger requirements. The buffer is circular so all the time that the
card is waiting for trigger samples are being stored away into
SRAM. When triggered, the READ POINTER freezes.
Conversions continue until the WRITE POINTER equals the READ
POINTER. Then the system halts and generates an interrupt. The
PC reads out the sample data from the SRAM for display /
processing.
The maximum sample rate in this mode is 500KSPS (or 600KSPS
for the AD1x6). This gives a buffer fill time of 32.768ms.
The slowest sample rate is 305SPS giving a buffer fill time of 53.7s.