NEC 78014Y Series, User Manual

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CHAPTER 14 A/D CONVERTER
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(1) Successive approximation register (SAR)
This register compares the analog input voltage value to the voltage tap (compare voltage) value applied from
the series resistor string and holds the result from the most significant bit (MSB).
When up to the least significant bit (LSB) is held (termination of A/D conversion), the SAR contents are transferred
to the A/D conversion result register (ADCR).
(2) A/D conversion result register (ADCR)
This register holds the A/D conversion result. Each time A/D conversion terminates, the conversion result is
loaded from the successive approximation register (SAR).
ADCR is read with an 8-bit memory manipulation instruction.
RESET input makes ADCR undefined.
(3) Sample & hold circuit
The sample & hold circuit samples each analog input signal sequentially applied from the input circuit and sends
it to the voltage comparator. This circuit holds the sampled analog input voltage value during A/D conversion.
(4) Voltage comparator
The voltage comparator compares the analog input to the series resistor string output voltage.
(5) Series resistor string
The series resistor string is connected to among AV
REF
to AV
SS
and generates a voltage to be compared to the
analog input.
(6) ANI0 to ANI7 pins
These are 8-channel analog input pins to input analog signals to undergo A/D conversion to the A/D converter.
These pins except analog input pins selected with the A/D converter input select register (ADIS) can be used
as the input/output port.
Cautions 1. Use ANI0 to ANI7 input voltages within the specified range. If a voltage higher than AV
REF
or lower than AV
SS
is applied (even if within the absolute maximum ratings), the converted
value of the corresponding channel will be undefined and may adversely affect the
converted values of other channels.
2. Pins ANI0/P10 to ANI7/P17
The analog input pins ANI0 to ANI7 also function as input/output port (PORT1) pins. Pins
used as the analog input should be specified to the input mode.
When A/D conversion is performed with any of pins ANI0 to ANI7 selected, be sure not to
execute a PORT1 input instruction while conversion is in progress, as this may reduce the
conversion resolution.
Also, if digital pulses are applied to a pin adjacent to the pin in the process of A/D
conversion, the expected A/D conversion value may not be obtainable due to coupling
noise. Therefore, avoid applying pulses to pins adjacent to the pin undergoing A/D
conversion.