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CHAPTER 13
A/D CONVERTER
User’s Manual U12697EJ4V1UD
(1) Successive approximation register (SAR)
Compares the voltage of the analog input with the voltage tap (comparison voltage) from the series resistor string,
and saves the result from the most significant bit (MSB).
The contents of SAR will be transmitted across to the A/D conversion result register after the least significant
bit (LSB) is saved (A/D conversion finished).
(2) A/D conversion result register (ADCR)
Holds A/D conversion results. At the end of each A/D conversion operation, the conversion result from the
successive approximation register is loaded.
ADCR is read with an 8-bit memory manipulation operation.
RESET input makes ADCR undefined.
(3) Sample & hold circuit
Samples analog inputs one by one as they are sent from the input circuit, and sends them to the voltage
comparator. The sampled analog input voltages are saved during A/D conversion.
(4) Voltage comparator
Compares the analog input voltage with the output voltage of the series resistor string.
(5) Series resistor string
Placed between AVDD and AVSS, generates the voltage that is compared with that of the analog input signal.
(6) ANI0 to ANI7 pins
Eight analog input channels used for inputting analog data to the A/D converter for A/D conversion. Pins not
selected for analog input with the A/D converter input selection register (ADIS) can be used as input ports.
Cautions 1. Use the ANI0 to ANI7 input voltages within the rated voltage range. Inputting a voltage
equal to or greater than AVDD, or equal to or smaller than AVSS (even if within the absolute
maximum rated range) will cause the channel’s conversion values to become undefined,
or may affect the conversion values of other channels.
2. Analog input pins (AN10 to AN17) function alternately as input port pins (P10 to P17).
When performing an A/D conversion with any one of the AN10 to AN17 inputs selected,
do not execute input instructions to port 1 during conversion, otherwise the conversion
resolution may decrease. When a digital pulse is applied to a pin that adjoins the pin
undergoing A/D conversion, the expected A/D conversion value may not be acquired due
to coupling noise. Therefore do not apply a pulse to a pin that adjoins the pin undergoing
A/D conversion.
(7) AVSS pin
Ground pin of the A/D converter. Always use this pin at the same potential as the VSS pin, even when not using
the A/D converter.
(8) AVDD pin
Analog power supply pin and reference voltage input pin of the A/D converter. Always use this pin at the same
potential as the VDD pin, even when not using the A/D converter.