788
Chapter 20
A/D Converter (ADC)
Preliminary User’s Manual U17566EE1V2UM00
20.5 Cautions
(1)
When A/D Converter is not used
When the A/D Converter is not used, the power consumption can be reduced
by clearing the ADA0CE bit of the ADA0M0 register to 0.
(2)
Input range of ANIn pins
Input the voltage within the specified range to the ANIn pins. If a voltage equal
to or higher than AV
REF
or equal to or lower than AV
SS
(even within the range of
the absolute maximum ratings) is input to any of these pins, the conversion
value of that channel is undefined.
(3)
Countermeasures against noise
To maintain the 10-bit resolution, the ANIn pins must be effectively protected
from noise. The influence of noise increases as the output impedance of the
analog input source becomes higher. To lower the noise, connecting an
external capacitor as shown in
Figure 20-8
is recommended.
Figure 20-8
Processing of analog input pin
(4)
Alternate I/O
The analog input pins ANIn function alternately as port pins. When selecting
one of the ANIn pins to execute A/D conversion, do not execute an instruction
to read an input port or write to an output port during conversion as the
conversion resolution may drop.
If a digital pulse is applied to a pin adjacent to the pin whose input signal is
being converted, the A/D conversion value may not be as expected due to the
influence of coupling noise. Therefore, do not apply a pulse to a pin adjacent to
the pin undergoing A/D conversion.
AV
REF
V
DD
V
SS
AV
SS
Cl
a
mp with
a
diode with
a
low V
F
(0.
3
V or le
ss
)
if noi
s
e e
qua
l to or higher th
a
n AV
REF
or e
qua
l
to or lower th
a
n AV
SS
m
a
y
b
e gener
a
ted.
C = 100 to 1,000 pF
ANI0 to ANI15
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