MC908GR32AVFAE Datasheet, PDF (64/314 Pages) Freescale Semiconductor, Inc – Microcontrollers

Analog-to-Digital Converter (ADC)
down the ADC by setting ADCH4–ADCH0 bits in the ADC status and control register before executing the
WAIT instruction.
3.6.2 Stop Mode
The ADC module is inactive after the execution of a STOP instruction. Any pending conversion is aborted.
ADC conversions resume when the MCU exits stop mode after an external interrupt. Allow one
conversion cycle to stabilize the analog circuitry.
3.7 I/O Signals
The ADC module has eight pins shared with port A and the KBI module:
PTA7/KBD7/AD15–PTA0/KBD0/AD8
The ADC module has eight pins shared with port B:
PTB7/AD7–PTB0/AD0
The ADC module has eight pins shared with port G:
PTG7/AD23–PTG0/AD16
3.7.1 ADC Analog Power Pin (V_DDAD)
The ADC analog portion uses V_DDAD as its power pin. Connect the V_DDAD pin to the same voltage
potential as V_DD. External filtering may be necessary to ensure clean V_DDAD for good results.
NOTE
For maximum noise immunity, route V_DDAD carefully and place bypass
capacitors as close as possible to the package.
V_DDAD and V_REFH are bonded internally.
3.7.2 ADC Analog Ground Pin (V_SSAD)
The ADC analog portion uses V_SSAD as its ground pin. Connect the V_SSAD pin to the same voltage
potential as V_SS.
NOTE
Route V_SSAD cleanly to avoid any offset errors.
V_SSAD and V_REFL are bonded internally.
3.7.3 ADC Voltage Reference High Pin (V_REFH)
The ADC analog portion uses V_REFH as its upper voltage reference pin. By default, connect the V_REFH
pin to the same voltage potential as V_DD. External filtering is often necessary to ensure a clean V_REFH for
good results. Any noise present on this pin will be reflected and possibly magnified in A/D conversion
values.
NOTE
For maximum noise immunity, route V_REFH carefully and place bypass
capacitors as close as possible to the package. Routing V_REFH close and
parallel to V_REFL may improve common mode noise rejection.
V_DDAD and V_REFH are bonded internally.
MC68HC908GR60A • MC68HC908GR48A • MC68HC908GR32A Data Sheet, Rev. 5
64
Freescale Semiconductor