16.2 Select the Input Channel

To select the input channel to read, write a low-channel/high-channel pair to the channel register at Base+2. The low four bits select the low channel, and the high four bits select the high channel. When you write any value to this register, the current A/D channel is set to the low channel.

For example, to program the board to sample channel 4 only, write 0x44 to Base+2. To program the board to sample channels 0 through 15 in sequence, write 0xF0 to Base+2.

When you perform an A/D conversion, the current channel automatically increments to the next channel in the selected range. Therefore, to perform A/D conversions on a group of consecutively-numbered channels, you do not need to write the input channel prior to each conversion. For example, to read from channels 0 - 2, write 0x20 to base+2. The first conversion is on channel 0, the second will be on channel 1 and the third will be on channel 2. The channel counter wraps around to the beginning so the fourth conversion will be on channel 0 again.

outp(base+2, 0x22); // example, set channel range to fixed channel 2

outp(base+2, 0x70); // example, set channel range to 0-7