Analog-to-Digital Converter (ADC)
I/O Signals
MC68HC08AS32A — Rev. 1
Data Sheet
MOTOROLA
Analog-to-Digital Converter (ADC)
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57
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.
Allow one conversion cycle to stabilize the analog circuitry before attempting a new
ADC conversion after exiting stop mode.
3.6 I/O Signals
The ADC module has 15 channels that are shared with I/O ports B and D and one
channel with an input-only port bit on port D. Refer to
18.7 ADC Characteristics
for voltages referenced in the next three subsections.
3.6.1 ADC Analog Power Pin (V
DDA
/V
DDAREF
)/ADC Voltage Reference Pin (V
REFH
)
The ADC analog portion uses V
DDA
/V
DDAREF
as its power pin. Connect the
V
DDA
/V
DDAREF
pin to the same voltage potential as V
DD
. External filtering may be
necessary to ensure clean V
DDA
/V
DDAREF
for good results.
V
REFH
is the high reference voltage for all analog-to-digital conversions.
NOTE:
Route V
DDA
/V
DDAREF
carefully for maximum noise immunity and place bypass
3.6.2 ADC Analog Ground Pin (V
SSA
)/ADC Voltage Reference Low Pin (V
REFL
)
The ADC analog portion uses V
SSA
as its ground pin. Connect the V
SSA
pin to the
same voltage potential as V
SS
. V
REFL
is the lower reference supply for the ADC.
3.6.3 ADC Voltage In (ADCVIN)
ADCVIN is the input voltage signal from one of the 15 ADC channels to the ADC
module.
3.7 I/O Registers
These I/O registers control and monitor ADC operation:
ADC status and control register (ADSCR)
ADC data register (ADR)
ADC input clock register (ADICLK)
F
Freescale Semiconductor, Inc.
n
.