MC68HC908GT16_07 Datasheet, PDF (53/292 Pages) Freescale Semiconductor, Inc – Microcontrollers

I/O Signals
3.5.2 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.
3.6 I/O Signals
The ADC module has eight pins shared with port B, PTB7/AD7–PTB0/AD0.
3.6.1 ADC Analog Power Pin (V_DDA)
The ADC analog portion uses V_DDA as its power pin. Connect the V_DDA pin to the same voltage potential
as V_DD. External filtering may be necessary to ensure clean V_DDA for good results.
NOTE
For maximum noise immunity, route V_DDA carefully and place bypass
capacitors as close as possible to the package.
3.6.2 ADC Analog Ground Pin (V_SSA)
The ADC analog portion uses V_SSA as its ground pin. Connect the V_SSA pin to the same voltage potential
as V_SS.
NOTE
Route V_SSA cleanly to avoid any offset errors.
3.6.3 ADC Voltage Reference High Pin (V_REFH)
The ADC analog portion uses V_REFH as its upper voltage reference pin. The V_REFH pin must be connected
to the same voltage potential as V_DDA. 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.
3.6.4 ADC Voltage Reference Low Pin (V_REFL)
The ADC analog portion uses V_REFL as its lower voltage reference pin. The V_REFL pin must be connected
to the same voltage potential as V_SSA. External filtering is often necessary to ensure a clean V_REFL 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_REFL carefully and, if not connected
to V_SS, 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.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
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