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CHAPTER 13 A/D CONVERTER
User’s Manual U14260EJ3V1UD
(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 A/D conversion result register 0 (ADCR0).
(6) A/D conversion result register 0 (ADCR0)
The result of A/D conversion is loaded from the successive approximation register (SAR) to this register each
time A/D conversion is completed, and the ADCR0 register holds the result of A/D conversion in its higher 10
bits (the lower 6 bits are fixed to 0).
(7) Controller
After A/D conversion has been completed, INTAD0 is generated.
(8) AV
REF
pin
This pin inputs an analog power/reference voltage to the A/D converter. When using the A/D converter, supply
the power. Connect directly to V
SS0
or V
SS1
when the A/D converter is not used.
The signal input to ANI0 to ANI7 is converted into a digital signal, based on the voltage applied across AV
REF
and AV
SS
.
Caution
A series resistor string is connected between the AV
REF
and AV
SS
pins. Therefore, when the
output impedance of the reference voltage is too high, it seems as if the AV
REF
pin and the
series resistor string are connected in series. This may cause a greater reference voltage
error.
(9) AV
SS
pin
This is the ground potential pin of the A/D converter. Always use this pin at the same potential as that of the
V
SS
pin even when the A/D converter is not used.
(10) ADTRG pin
This pin is used to start the A/D converter by hardware.
(11) A/D converter mode register 0 (ADM0)
This register is used to set the conversion time of the analog input signal to be converted, and to start or stop
the conversion operation.
(12) Analog input channel specification register 0 (ADS0)
This register is used to specify the port that inputs the analog voltage to be converted into a digital signal.