NEC PD78058FY(A) - Manual (Page 264)

264
CHAPTER 14 A/D CONVERTER
(1) Successive approximation register (SAR)
The analog input voltage value and the voltage tap (comparative voltage) value from the serial resistance string
are compared and the results are stored in this register from the most significant bit (MSB).
If values are stored to the least significant bit (LSB) (after A/D conversion), the contents of the SAR are
transferred to the A/D conversion results 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 serial resistance string is connected between AV REF0 and AV SS , and generates voltages which are
compared to analog inputs.
(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.
Pins other than those selected as analog input by the A/D converter input select register (ADIS) can be used
as input/output ports.
Cautions 1. Use ANI0 to ANI7 input voltages within the specified range. If a voltage higher than
AVREF0 or lower than AVSS is applied (even if within the absolute maximum ratings),
the converted value of the corresponding channel becomes indeterminate and may
adversely affect the converted values of other channels.
2. Pins ANI0 to ANI7 are also used as I/O port (port 1) pins. If one of pins ANI0 to ANI7 is
selected to perform A/D conversion, do not execute an input instruction for port 1 during
conversion, as this could lower the conversion resolution.
Also, if a digital pulse is applied to a pin that is adjacent to a pin for which A/D conversion
is being performed, it is possible that the A/D conversion value will not be as expected
due to coupling noise. Therefore, do no apply a pulse to a pin adjacent to a pin for which
A/D conversion is being performed.