CHAPTER 12 A/D CONVERTER
Preliminary User’s Manual U16315EJ1V0UD
227
(3) Sample & hold circuit
The sample & hold circuit samples each analog input signal sequentially applied from the input circuit, and sends
it to the voltage comparator. This circuit holds the sampled analog input voltage value during A/D conversion.
(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 AV
REF
and AV
SS
, 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 AV
REF
or higher or
a voltage of AV
SS
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) AV
REF
pin
The AV
REF
pin inputs the A/D converter reference voltage.
It converts signals input to ANI0 to ANI7 into digital signals based on a voltage between AV
REF
and AV
SS
.
In a standby mode, the current flowing into series resistor strings can be reduced by changing the input voltage of
the AV
REF
pin to AV
SS
level.
It can also be used as the analog power supply. When the A/D converter is used, be sure to use the AV
REF
pin
for the power supply.
Caution
A series resistor string of several tens of k
Ω
Ω
Ω
Ω
is connected between the AV
REF
and AV
SS
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 AV
REF
and AV
SS
pins, resulting in a
large reference voltage error.
(8) AV
SS
pin
The AV
SS
pin is the GND potential pin for the A/D converter. Always use the AV
SS
pin at the same potential as
the V
SS0
pin, even when the A/D converter is not used.