A/D Data Transfer - Advantech PCM-3718 Series User Manual

5.5 A/D Data Transfer

You can perform A/D data transfer by Program Control, Interrupt Rou-
tine or DMA.
1. Program controlled data transfer operates by polling the A/D status
register. After the A/D conversion has been triggered, your applica-
tion program checks the INT bit (data valid) of the A/D status regis-
ter. When it detects that the INT bit is on (1), it sends the A/D data
to the PC's memory using DMA. Reset the INT bit (by writing to
register BASE+8 with any value) after you transfer the A/D data.
When you use software triggering, you can check either the INT or
EOC bits for data validity. Since you use the program to trigger the
A/D conversion, you do not need to poll the INT bit to see if the con-
version has occurred. It is easier to use the EOC bit, because you do
not need to clear it after you transfer the data.
2. With interrupt data transfer, you write an interrupt routine handler
program, which transfers data from the module's A/D data registers
to a previously defined memory segment in the PC. At the end of
each conversion, the EOC signal generates an interrupt, and the
interrupt handler routine performs the transfer. You must specify the
interrupt control bit and the interrupt level selection bits in the PCM-
3718's control register (BASE+9) before using the interrupt rou-
tine. Writing to the A/D status register address (BASE+8) resets the
PCM-3718's interrupt request and re-enables the PCM-3718's inter-
rupt.
3. Direct Memory Access (DMA) Transfer moves the A/D data from
the PCM-3718's hardware device to the PC system memory without
the system CPU. DMA is very useful in high-speed data transfers,
but it is complicated to operate. Before the DMA operation you must
set the DMA level (JP1), the DMA enable bit control register
(BASE+9) and the registers in the 8237 DMA controller. We recom-
mend that you use the PCM-3718 driver to perform DMA opera-
tions. See Chapter 8 for more Information on the 8237 DMA
controller and PCM-3718 operations.
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