Freescale Semiconductor MC68HC908MR32 - Manual (Page 50)

Analog-to-Digital Converter (ADC)
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
50 Freescale Semiconductor
3.4 Interrupts
When the AIEN bit is set, the ADC module is capable of generating a CPU interrupt after each ADC
conversion. A CPU interrupt is generated if the COCO bit is at 0. The COCO bit is not used as a
conversion complete flag when interrupts are enabled.
3.5 Wait Mode
The WAIT instruction can put the MCU in low power-consumption standby mode.
The ADC continues normal operation during 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 ADCH[4:0] in the ADC status and control register before executing the WAIT
instruction.
3.6 I/O Signals
The ADC module has 10 input signals that are shared with port B and port C.
3.6.1 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
Route V
DDAD
carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
3.6.2 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
.
3.6.3 ADC Voltage Reference 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
DDAD
. There will be a finite current associated with V
REFH
. See Chapter 19 Electrical
Specifications .
NOTE
Route V
REFH
carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
3.6.4 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
SSAD
. A finite current will be associated with V
REFL
. See Chapter 19 Electrical Specifications .
NOTE
In the 56-pin shrink dual in-line package (SDIP), V
REFL
and V
SSAD
are tied
together.