Datasheet

Analog-to-Digital Converter (ADC)
MC68HC908AP Family Data Sheet, Rev. 4
252 Freescale Semiconductor
15.5.1 Wait Mode
The ADC continues normal operation in wait mode. Any enabled CPU interrupt request from the ADC can
bring the MCU out of wait mode. If the ADC is not required to bring the MCU out of wait mode, power
down the ADC by setting the ADCH[4:0] bits to logic 1’s before executing the WAIT instruction.
15.5.2 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. Allow one conversion cycle to stabilize the
analog circuitry before attempting a new ADC conversion after exiting stop mode.
15.6 I/O Signals
The ADC module has eight channels shared with port A I/O pins.
15.6.1 ADC Voltage In (V
ADIN
)
V
ADIN
is the input voltage signal from one of the eight ADC channels to the ADC module.
15.6.2 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
Route V
DDA
carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
15.6.3 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
.
15.6.4 ADC Voltage Reference High Pin (V
REFH
)
V
REFH
is the power supply for setting the reference voltage V
REFH
. Connect the V
REFH
pin to the same
voltage potential as V
DDA
. There will be a finite current associated with V
REFH
(see Chapter 22 Electrical
Specifications).
NOTE
Route V
REFH
carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
15.6.5 ADC Voltage Reference Low Pin (V
REFL
)
V
REFL
is the lower reference supply for the ADC. Connect the V
REFL
pin to the same voltage potential as
V
SSA
. There will be a finite current associated with V
REFL
(see Chapter 22 Electrical Specifications).