Freescale Semiconductor MC68HC908MR32 - Manual (Page 47)

Functional Description
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor 47
Figure 3-2. ADC Block Diagram
3.3.1 ADC Port I/O Pins
PTC1/ATD9:PTC0/ATD8 and PTB7/ATD7:PTB0/ATD0 are general-purpose I/O pins that are shared with
the ADC channels.
The channel select bits define which ADC channel/port pin will be used as the input signal. The ADC
overrides the port logic when that port is selected by the ADC multiplexer. The remaining ADC
channels/port pins are controlled by the port logic and can be used as general-purpose input/output (I/O)
pins. Writes to the port register or DDR will not have any effect on the port pin that is selected by the ADC.
Read of a port pin which is in use by the ADC will return a 0.
3.3.2 Voltage Conversion
When the input voltage to the ADC equals V
REFH
, the ADC converts the signal to $3FF (full scale). If the
input voltage equals V
REFL
, the ADC converts it to $000. Input voltages between V
REFH
and V
REFL
are
straight-line linear conversions. All other input voltages will result in $3FF if greater than V
REFH
and $000
if less than V
REFL
.
NOTE
Input voltage should not exceed the analog supply voltages. See
19.13 Analog-to-Digital Converter (ADC) Characteristics .
READ PTB/PTC
PTB/Cx
INTERRUPT
LOGIC
CHANNEL
SELECT
ADC
CLOCK
GENERATOR
CONVERSION
COMPLETE
ADC VOLTAGE IN
ADVIN
ADC CLOCK
CGMXCLK
BUS CLOCK
ADCH[4:0]
ADC DATA REGISTERS
ADIV[2:0] ADICLK
AIEN COCO
DISABLE
ADC CHANNEL x
INTERNAL
DATA BUS