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CHAPTER 14 A/D CONVERTER
(1) Successive approximation register (SAR)
Compares the voltage of the analog input with the voltage tap (comparison voltage) from the series resistor string,
and retains the result from the most significant bit (MSB).
When retaining the result to the least significant bit (LSB) (A/D conversion end), the contents of the SAR register
are transferred to the A/D conversion result register.
(2) A/D conversion result register (ADCR)
Retains 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 its contents undefined.
Caution
Do not read ADCR during A/D conversion operation stop (ADCS (bit 7 of A/D converter mode
register (ADM) = 0). If do, an undefined value is read.
(3) Sample & hold circuit
Samples analog input signals 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
Connected between AV
REF0
and AV
SS
, generates the voltage that is compared with that of analog input.
(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 convertor input selection register (ADIS) can be used as input ports.
Cautions 1. Use ANI0 to ANI7 input voltages within the rated voltage range. Inputting a voltage equal
to or greater than AV
REF0
, or equal to or smaller than AV
SS
(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 (AN10 to AN17) pins alternate with input port (P10 to P17) pins. When
performing an A/D conversion with the selection of any one of inputs from AN10 to AN17,
do not execute input instructions to port 1 during conversion. Conversion resolution may
decrease. When a digital pulse is applied to the pin which adjoins a pin in the A/D
conversion, an expected A/D conversion value may not be acquired due to the coupling
noise. Therefore do not apply a pulse to the pin which adjoins the pin in the A/D
conversion.
(7) AV
REF0
pin
Used to input the reference voltage of the A/D converter.
Based on the voltage applied between AV
REF0
and AV
SS
, signals input to ANI0 to ANI7 are converted to digital
signals.