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12.2 Configuration of A/D Converter
The A/D converter includes the following hardware.
Registers
(1) ANI0 to ANI7 pins
These are the analog input pins of the 8-channel A/D converter. They input analog signals to be converted into
digital signals. Pins other than the one selected as the analog input pin by the analog input channel specification
register (ADS) can be used as input port pins.
(2) Sample & hold circuit
The sample & hold circuit samples the input signal of the analog input pin selected by the selector when A/D
conversion is started, and holds the sampled analog input voltage value during A/D conversion.
(3) Series resistor string
The series resistor string is connected between AV
the analog input signal.
(4) Voltage comparator
The voltage comparator compares the sampled analog input voltage and the output voltage of the series resistor
string.
(5) Successive approximation register (SAR)
This register compares the sampled analog voltage and the voltage of the series resistor string, and converts the
result, starting from the most significant bit (MSB).
When the voltage value is converted into a digital value down to the least significant bit (LSB) (end of A/D
conversion), the contents of the SAR register are transferred to the A/D conversion result register (ADCR).
CHAPTER 12 A/D CONVERTER
Table 12-1. Registers of A/D Converter Used on Software
Item
A/D conversion result register (ADCR)
A/D converter mode register (ADM)
Analog input channel specification register (ADS)
Power-fail comparison mode register (PFM)
Power-fail comparison threshold register (PFT)
Figure 12-2. Circuit Configuration of Series Resistor String
AV
REF
P-ch
AV
SS
User's Manual U16899EJ2V0UD
Configuration
and AV
, and generates a voltage to be compared with
REF
SS
ADCS
Series resistor string
247
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