User`s guide

Operation Theory • 37
It's recommended that this mode be used if the application requires a fixed and
precise A/D sampling rate.
External Trigger (EITS=1, TPST=don‘t care)
Through pin-16 of CN3 (ExtTrig), an A/D conversion can also be triggered by
an external signal. The A/D conversion starts when ExtTrig changes from a
high to a low level. The conversion rate in this mode is more flexible depending
on the available trigger options of the external device. The external trigger can
be also combined with the FIFO half interrupt, EOC interrupt or program FIFO
polling for transferring data.
4.1.4 A/D Data Transfer Modes
The A/D data are buffered in the FIFO memory. The FIFO size of the PCI-9111
is 1024 (1K) words. If the sampling rate is 100 KHz, the FIFO can buffer 10.24
ms of analog signal. Data transferred to the FIFO after the FIFO is full will be
lost. The software must read out the FIFO data before it becomes full.
The data must be transferred to the host memory after the data is ready and
before the FIFO is full. With the PCI-9111, Different transfer modes can be
used. The different transfer modes are described below:
Software Data Polling
The software data polling is the easiest way to transfer A/D data. This mode
can be used with software A/D trigger mode. After the A/D conversion is
triggered by software, the software should poll the FF_EF bit of the A/D status
register until it becomes low level.
If the FIFO is empty before the A/D start, the FF_EF bit will be low. After the
A/D is completed, the A/D data is written to FIFO immediately, therefore the
FF_EF becomes high. You can consider the FF_EF bit as converted data
ready status. That is, FF_EF is high means the data is ready. Note that, while
A/D is converted, the ADBUSY bit is low. After A/D conversion, the ADBUSY
become high to indicate not busy. Please do NOT use this bit to poll the AD
data.
It is possible to read A/D converted data without polling. The A/D conversion
time will not exceed 8.5µs on PCI-9111 card. Hence, after software trigger, the
software can wait for at least 8.5µs then read the A/D register without polling.
The data polling transferring is very suitable for applications that need to
process AD data in real time. Especially when combining with the timer
interrupt generation, the timer interrupt service routine can use the data polling
method to get multi-channel A/D data in real time and under fixed data
sampling rates.