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(2) Input range of ANI0 to ANI7
The input voltages of ANI0 to ANI7 should be within the specification range. In particular, if a voltage above AV
or below AV
will be indeterminate. The conversion values of the other channels may also be affected.
(3) Noise countermeasures
In order to maintain 8-bit resolution, attention must be paid to noise on pins AV
effect increases in proportion to the output impedance of the analog input source, it is recommended that a
capacitor is connected externally as shown in Figure 14-9 in order to reduce noise.
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(4) Pins ANI0/P10 to ANI7/P17
The analog input pins ANI0 to ANI7 also function as input/output port (PORT1) pins. Pins used as the analog
input should be specified to the input mode.
When A/D conversion is performed with any of pins ANI0 to ANI7 selected, be sure not to execute a PORT1 input
instruction while conversion is in progress, as this may reduce the conversion resolution.
Also, if digital pulses are applied to a pin adjacent to the pin in the process of A/D conversion, the expected
A/D conversion value may not be obtainable due to coupling noise. Therefore, avoid applying pulses to pins
adjacent to the pin undergoing A/D conversion.
(5) AV
pin input impedance
REF
A series resistor string of approximately 10 kΩ is connected between the AV
Therefore, if the output impedance of the reference voltage source is high, this will result in parallel connection
to the series resistor string between the AV
error.
260
CHAPTER 14 A/D CONVERTER
is input (even if within the absolute maximum rating range), the conversion value for that channel
SS
Figure 14-9. Analog Input Pin Disposition
Reference
Voltage Input
C = 100 to 1000 pF
If there is a possibility that a noise level of
AV
or higher or AV
REF
clamp with a small diode with V
AV
REF
ANI0 to ANI7
V
DD
V
DD
AV
DD
AV
SS
V
SS
pin and the AV
pin, and there will be a large reference voltage
REF
SS
and ANI0 to ANI7. Since the
REF
or lower may enter,
SS
(0.3 V or less).
F
pin and the AV
pin.
REF
SS
REF
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