Advantech Carbon Monoxide Alarm PCI-1718 Series User Manual

The write register at BASE+02H controls multiplexer (MUX) scanning. 
The high nibble provides the stop scan channel number, and the low nib-
ble provides the start scan channel number. Writing to this register auto-
matically initializes the MUX to the start channel. Each A/D conversion 
trigger sets the MUX to the next channel.
With continuous triggering the MUX will scan from the start channel to 
the end channel, then repeat. For example, if the start channel is 3 and the 
stop channel is 7, then the scan sequence is 3, 4, 5, 6, 7, 3, 4, 5, 6, 7, 3, 4.

CH3 ~ CH0 

Stop scan channel number

CH0 

The least significant bit (LSB) of the stop channel

CH3 

The most significant bit (MSB)

CL3 ~ CL0 

Start scan channel number

CL0 

The least significant bit (LSB) of the start channel

CL3 

The most significant bit (MSB)

The MUX scan register low nibble, CL3 to CL0, also acts as a pointer 
when you program the A/D input range (see previous section). When you 
set the MUX start channel to N, the range code written to the register 
BASE+01H is for channel N.

Programming example for PCI-1718HDU
This BASIC code fragment sets the range for channel 5 to ±0.625 V:
200  OUT BASE+2, 5   'SET POINTER TO CH.5
210  OUT BASE+1, 3   'RANGE CODE=3 FOR ±0.625 V

Write

MUX scan channel control

Bit  #

7

6

5

4

3

2

1

0

BASE + 02H

CH3

CH2

CH1

CH0

CL3

CL2

CL1

CL0