Datasheet

I/O Registers
MC68HC908GZ60 • MC68HC908GZ48 • MC68HC908GZ32 Data Sheet, Rev. 6
Freescale Semiconductor 67
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.
3.7.4 ADC Voltage Reference Low Pin (V
REFL
)
The ADC analog portion uses V
REFL
as its lower voltage reference pin. By default, connect the V
REFL
pin
to the same voltage potential as V
SS
. 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.
V
SSAD
and V
REFL
are bonded internally.
3.7.5 ADC Voltage In (V
ADIN
)
V
ADIN
is the input voltage signal from one of the 24 ADC channels to the ADC module.
3.8 I/O Registers
These I/O registers control and monitor ADC operation:
• ADC status and control register (ADSCR)
• ADC data register (ADRH and ADRL)
• ADC clock register (ADCLK)