232
CHAPTER 13 A/D CONVERTER
User’s Manual U12697EJ3V0UM
(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 AV
DD
and AV
SS
, generates the voltage that is compared with that of 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 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
DD
, 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
SS
pin
Ground pin of the A/D converter. Always use this pin at the same potential as the V
SS
pin, even when not using
the A/D converter.
(8) AV
DD
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 V
DD
pin, even when not using the A/D converter.
