CHAPTER 12 A/D CONVERTER
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User’s Manual U11302EJ4V0UM
(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
greater than or equal to AV
REF
or less than or equal to AV
SS
is input (even if within the absolute maximum
rating range), the conversion value for that channel will be undefined, and 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 the AV
REF
and ANI0 to ANI7 pins.
Since the effect increases in proportion to the output impedance of the analog input source, it is
recommended that a capacitor be connected externally as shown in Figure 12-9 in order to reduce noise.
Figure 12-9. Analog Input Pin Processing
(4) Pins ANI0/P10 to ANI7/P17
The analog input pins ANI0 to ANI7 also function as I/O port (port 1) pins.
Pins used as analog inputs should be set to the input mode.
When A/D conversion is performed with any of pins ANI0 to ANI7 selected, be sure not to execute an
instruction that inputs data to port 1 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
REF
pin input impedance
A series resistor string of approximately 10 k
Ω
is connected between the AV
REF
pin and the AV
SS
pin.
Therefore, if the output impedance of the reference voltage source is high, this will result in series
connection to the series resistor string between the AV
REF
pin and the AV
SS
pin, and there will be a large
reference voltage error.
Reference
voltage input
AV
REF
ANI0 to ANI7
V
DD
AV
DD
AV
SS
V
SS
C = 100 to
1000 pF
If there is possibility that noise whose
level is AV
REF
or higher or AV
SS
or lower may enter,
clamp with a diode with a small V
F
(0.3 V or less).
AV
REF