
Analog-to-Digital (A/D) Converter
Data Sheet
M68HC11E Family — Rev. 5
70
Analog-to-Digital (A/D) Converter
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MOTOROLA
system is configured to perform a conversion on each of four channels where 
each result register corresponds to one channel. 
NOTE:
When the multiple-channel continuous scan mode is used, extra care is needed in 
the design of circuitry driving the A/D inputs. The charge on the capacitive DAC 
array before the sample time is related to the voltage on the previously converted 
channel. A charge share situation exists between the internal DAC capacitance 
and the external circuit capacitance. Although the amount of charge involved is 
small, the rate at which it is repeated is every 64 
μ
s for an E clock of 2 MHz. The 
RC charging rate of the external circuit must be balanced against this charge 
sharing effect to avoid errors in accuracy. Refer to M68HC11 Reference Manual, 
Motorola document order number M68HC11RM/AD, for further information. 
CD:CA — Channel Selects D:A Bits
Refer to 
Table 3-2
. When a multiple channel mode is selected (MULT = 1), the 
two least significant channel select bits (CB and CA) have no meaning and the 
CD and CC bits specify which group of four channels is to be converted. 
Table 3-2. A/D Converter Channel Selection
Channel Select 
Control Bits
CD:CC:CB:CA 
0000
0001
0010
0011
0100
0101
0110
0111
10XX
Channel Signal
Result in ADRx
if MULT = 1 
AN0
AN1
AN2
AN3
AN4
AN5
AN6
AN7
ADR1 
ADR2 
ADR3 
ADR4 
ADR1 
ADR2 
ADR3 
ADR4 
— 
Reserved
1100
V
RH(1)
1. Used for factory testing 
ADR1 
1101
V
RL(1)
ADR2 
1110
(V
RH
)/2
(1)
ADR3 
1111
Reserved
(1)
ADR4 
F
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n
.