Operation Theorem
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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 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 store 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.
ADLINK recommend user to check your system to find out the user software‘s
priority in the special application. If the application software is at the highest
priority, to poll the FIFO every 10 ms is suitable. However, the user‘s program
must check the FIFO is full or empty every time reading data.
To avoid this problem, the half-full polling method is used. If the A/D trigger rate
is 100KHz, the FIFO will be half-full (512 words) in 5.12 ms. If the user‘s
software checks the FIFO half full signal every 5 ms. When the FIFO is not
half-full, the software does not read data, because it is difficult to know how
much A/D data is stored in the FIFO and user must check the FIFO empty bit
every time reading data. When the FIFO is full, the AD FIFO is overrun. This
means the sampling rate is higher than users expect or the polling rate is too
slow, it is also possible due to your system occupy the CPU resource thus
reducing the polling rate. When the FIFO is half-full and not full, the software
can read one “block” (512 words) A/D data without check the FIFO status. This
method is very convenient to read A/D in size of a “block” and it is benefit to
software programming.
Usually, the timer trigger is used under this mode, therefore the sampling rate
is fixed. The method also utilizes the minimum CPU resources because it is not
necessary to be highest priority. The other benefit is this method will not use
hardware interrupt resource. Therefore, the interrupt is reserved for system
clock or emergency external interrupt request. The FIFO half-full polling
method is the most powerful A/D data transfer mode.
EOC Interrupt Transfer
The PCI-9111 provides traditional hardware end-of-conversion (EOC) interrupt
capability. Under this mode, an interrupt signal is generated when the A/D
conversion is ended and the data is ready to be read in the FIFO. It is useful to
combine the EOC interrupt transfer with the timer pacer trigger mode. After
A/D conversion is completed, the hardware interrupt will be inserted and its
corresponding ISR (Interrupt Service Routine) will be invoked and executed.
The converted data can be read by the ISR program. This method is most
suitable for data processing applications under real-time and fixed sampling
rate.
Summary of Contents for NuDAQ PCI-9111DG
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