CHAPTER 10 A/D CONVERTER
Preliminary User’s Manual U16846EJ1V0UD
183
10.2 Configuration of A/D Converter
The A/D converter includes the following hardware.
Table 10-1. Registers of A/D Converter Used on Software
Item Configuration
Registers
Successive approximation register (SAR)
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)
(1) ANI0 to ANI3 pins
These are the analog input pins of the 4-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
REF
and AV
SS
, and generates a voltage to be compared with
the analog input signal.
Figure 10-2. Circuit Configuration of Series Resistor String
AV
REF
AV
SS
P-ch
Series resistor string
ADCS
(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).