
CHAPTER 12 A/D CONVERTER
Preliminary User’s Manual U16228EJ1V0UD
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(4) Voltage comparator
The voltage comparator compares the analog input with the series resistor string output voltage.
(5) Series resistor string
The series resistor string is connected between AVREF and AVSS, and generates a voltage to be compared with
the analog input.
(6) ANI0 to ANI7 pins
These eight-channel analog input pins input analog signals to undergo A/D conversion to the A/D converter.
ANI0 to ANI7 are alternate-function pins that can also be used for digital input.
Cautions 1. Observe the rated range of the ANI0 to ANI7 input voltage. If a voltage of AVREF or higher or
a voltage of AVSS or lower (even if within the range of absolute maximum ratings) is input to
an analog input channel, the converted value of that channel becomes undefined.
In
addition, the converted values of the other channels may also be affected.
2. The analog input pins (ANI0 to ANI7) are also used as input port pins (P20 to P27). When
A/D conversion is performed with any of ANI0 to ANI7 selected, do not execute the input
instruction to port 2 while conversion is in progress; otherwise the conversion resolution
may be degraded. If a digital pulse is applied to the pins adjacent to the pins currently used
for A/D conversion, the expected value of the A/D conversion may not be obtained due to
coupling noise. Therefore, do not apply a pulse to the pins adjacent to the pin undergoing
A/D conversion.
(7) AVREF pin
The AVREF pin inputs the A/D converter reference voltage.
It converts signals input to ANI0 to ANI7 into digital signals based on a voltage between AVREF and AVSS.
In a standby mode, the current flowing into series resistor strings can be reduced by changing the input voltage of
the AVREF pin to AVSS level.
It can also be used as the analog power supply. When the A/D converter is used, be sure to use the AVREF pin
for the power supply.
Caution
A series resistor string of several tens of k
 is connected between the AVREF and AVSS pins.
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 AVREF and AVSS pins, resulting in a
large reference voltage error.
(8) AVSS pin
The AVSS pin is the GND potential pin for the A/D converter. Always use the AVSS pin at the same potential as
the VSS0 pin, even when the A/D converter is not used.