NXP Semiconductors MC9S08QL4, Reference Manual

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Analog-to-Digital Converter (S08ADC12V1)
MC9S08QL8 MCU Series Reference Manual, Rev. 1
126 NXP Semiconductors
10.2.1 Analog Power (V
DDA
)
The ADC analog portion uses V
DDA
as its power connection. In some packages, V
DDA
is connected
internally to V
DD
. If externally available, 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.
10.2.2 Analog Ground (V
SSA
)
The ADC analog portion uses V
SSA
as its ground connection. In some packages, V
SSA
is connected
internally to V
SS
. If externally available, connect the V
SSA
pin to the same voltage potential as V
SS
.
10.2.3 Voltage Reference High (V
REFH
)
V
REFH
is the high reference voltage for the converter. In some packages, V
REFH
is connected internally to
V
DDA
. If externally available, V
REFH
may be connected to the same potential as V
DDA
or may be driven
by an external source between the minimum V
DDA
spec and the V
DDA
potential (V
REFH
must never
exceed V
DDA
).
10.2.4 Voltage Reference Low (V
REFL
)
V
REFL
is the low-reference voltage for the converter. In some packages, V
REFL
is connected internally to
V
SSA
. If externally available, connect the V
REFL
pin to the same voltage potential as V
SSA
.
10.2.5 Analog Channel Inputs (ADx)
The ADC module supports up to 28 separate analog inputs. An input is selected for conversion through
the ADCH channel select bits.
10.3 Register Definition
These memory-mapped registers control and monitor operation of the ADC:
• Status and control register, ADCSC1
• Status and control register, ADCSC2
• Data result registers, ADCRH and ADCRL
• Compare value registers, ADCCVH and ADCCVL
• Configuration register, ADCCFG
• Pin control registers, APCTL1, APCTL2, APCTL3
10.3.1 Status and Control Register 1 (ADCSC1)
This section describes the function of the ADC status and control register (ADCSC1). Writing ADCSC1
aborts the current conversion and initiates a new conversion (if the ADCH bits are equal to a value other
than all 1s).