Motorola 68HC12, User Manual

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Table 2: Prescalar Values
Prescale Value
Divisor___
00000 Do not use
00001 /4
00010 /6
00011 /8
00100 /10
00101 /12
00110 /14
00111 /16
01xxx Do not use
1xxxx Do not use
_H12ADTCTL5 is used to select the conversion mode, which channels are to be
converted and to initiate the conversions. The conversion sequence is started by
any write made to this register. If a write is made to this register while a
conversion sequence is in progress, the conversion is aborted and the SCF and CCF
flags are reset.
_H12ADTCTL5:
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
unused
S8CM SCAN MULT CD CC CB CA
S8CM is used to select between making 4 conversions, when the bit is set to zero,
and 8 conversions, when the bit is set to one.
SCAN is used to select between performing either a single conversion or multiple
conversions. If SCAN is set to zero, then a single conversion will be run and the
flag will then be set. If SCAN is set to 1, then the A/D converter will run
continuous conversions on the A/D channels.
MULT determines whether the conversion is run on a single channel or on multiple
channels. When MULT zero, the A/D converter runs all the conversions on a single
channel, which is selected by CD,CC,CB, and CA. When MULT is one, the conversion
is run on several different channels in the group specified by CD,CC,CB, and CA.
The possible channel combinations are in Table 3.
Table 3: A/D Converter Settings
S8CM CD CC CB CA Channel Signal Result in ADRx if MULT = 1
0 0 0 0* 0* AN0 ADR0
0 0 0 0* 1* AN1 ADR1
0 0 0 1* 0* AN2 ADR2
0 0 0 1* 1* AN3 ADR3
0 0 1 0* 0* AN4 ADR0
0 0 1 0* 1* AN5 ADR1
0 0 1 1* 0* AN6 ADR2
0 0 1 1* 1* AN7 ADR3
0 1 0 0* 0* Reserved ADR0
0 1 0 0* 1* Reserved ADR1
0 1 0 1* 0* Reserved ADR2
0 1 0 1* 1* Reserved ADR3
0 1 1 0* 0* V RH ADR0
0 1 1 0* 1* V RL ADR1
0 1 1 1* 0* (V RH + V RL )/2 ADR2
0 1 1 1* 1* TEST/Reserved ADR3
1 0 0* 0* 0* AN0 ADR0
1 0 0* 0* 1* AN1 ADR1
1 0 0* 1* 0* AN2 ADR2