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67 Appendix C
C.6 MUX Scan Channel Control — BASE+02H
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
Table C.7: Register for MUX Scan Channel Control
Write MUX scan channel control
Bit # 7 6543210
BASE + 02H CH3 CH2 CH1 CH0 CL3 CL2 CL1 CL0
Note: The MUX start/stop channel changes each time
you change the input range. Do not forget to reset
the MUX start and stop channels to the correct
values after you finish setting the range.