NuDAQ PCI- 9113A User Manual page 38

The data must be transferred to host memory after the date is ready and
before the FIFO is full. On the PCI-9113A, many data transfer modes can
be used. The different transfer modes are specified as follows:
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 conversion is completed, the A/D data is written to FIFO immediately,
thus the FF_EF becomes high. You can consider the FF_EF bit as a flag
to indicate the 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 becomes 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 8.5 s on PCI-9113A card. Hence, after
software trigger, the software can wait for at least 8.5 s and then read
the A/D register without polling.
The data polling transfer is very suitable for the application that needs 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 with the
fixed data sampling rate.
FIFO Half-Full Polling
The FIFO half-full polling mode is the most powerful AD data transfer
mode. The 1 K words FIFO can be stored up to 10.24 ms analog data
under 100 KHz sampling rate (10.024ms = 1024 / 100 KHz ).
Theoretically, the software can poll the FIFO every 10 ms without taking
care how to trigger A/D or transfer A/D data.
It's recommend that users check your system to find out the user
software's priority in the special application. If the application software is
at the highest priority, polling the FIFO every 10 ms is suitable. However,
the user's program must check the FIFO is full or empty every time
28 Operation Theorem