Advantech 3718HG, User Manual, Page: 44 / 68

4 0 PCM-3718H/3718HG User's Manual
interrupt routine. Writing to the A/D status register address
(BASE+8) resets the PCM-3718H/3718HG interrupt request and re-
enables the PCM-3718H/3718HG interrupt.
3. Direct Memory Access (DMA) Transfer moves the A/D data from the
PCM-3718H/3718HG hardware device to the PC system memory
without the system CPU. DMA is very useful in high-speed data
transfer, 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 recommend that you use the PCM-3718H/3718HG driver to
perform DMA operations. See Chapter 8 for more Information on
the 8237 DMA controller and PCM-3718H/3718HG DMA opera-
tions.
5.6 How to Make an A/D Conversion
To perform A/D conversion, you can write all I/O port instructions
directly in your program, or you can take advantage of the PCM-
3718H/3718HG driver. We suggest that you apply the driver func-
tions in your program. This will make your programming job easier
and improve the program performance. See the User’s Manual of the
software driver for more information.
Do the following to perform software trigger and program controlled
data transfer without the PCM-3718H/3718HG driver:
1. Set the input range for each A/D channel.
2. Set the input channel by specifying the MUX scan range.
3. Trigger the A/D conversion by writing to the A/D low byte register
(BASE+0) with any value.
4. Check for the end of the conversion by reading the A/D status
register (BASE+8) INT bit.
5. Read data from the A/D converter by reading the A/D data registers
(BASE+0 and BASE+1).
6. Convert the binary A/D data to an integer.