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(1) Successive approximation register (SAR)
This register compares the analog input voltage value to the voltage tap (compare voltage) value applied
from the series resistor string and holds the result from the most significant bit (MSB).
When up to the least significant bit (LSB) is held (end of A/D conversion), the SAR contents are transferred
to the A/D conversion result register (ADCR).
(2) A/D conversion result register (ADCR)
This register holds the A/D conversion result. Each time A/D conversion ends, the conversion result is
loaded from the successive approximation register (SAR).
ADCR is read with an 8-bit memory manipulation instruction.
RESET input makes ADCR undefined.
(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
with the analog input.
(6) ANI0 to ANI7 pins
These are 8-channel analog input pins used to input the analog signals to undergo A/D conversion to
the A/D converter.
Except for the analog input pins selected by the A/D converter input select register (ADIS), these pins
can be used as I/O port pins.
Cautions 1. Use ANI0 to ANI7 input voltages within the specified range. If a voltage higher than
or equal to AV
maximum ratings), the converted value of the corresponding channel becomes
undefined and may adversely affect the converted values of other channels.
2. 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.
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.
undergoing A/D conversion.
192
CHAPTER 12 A/D CONVERTER
and AV
REF
or lower than or equal to AV
REF
Therefore, avoid applying pulses to pins adjacent to the pin
User's Manual U11302EJ4V0UM
and generates a voltage to be compared
SS
is applied (even if within the absolute
SS
When A/D conversion is
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