NEC uPD78P078 - Manual (Page 295)

295
CHAPTER 15 A/D CONVERTER
(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 the result of comparison is held to the least significant bit (LSB) (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.
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 between AV REF0 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.
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
AV REF0 or lower than AV SS 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. Analog input (ANI0 to ANI7) pins are alternate function pins corresponding to input/
output port (port 1) pin. When A/D conversion is performed with any one of ANI0 to ANI7
pins selected, do not execute input instruction to port 1 during conversion operation,
otherwise, the conversion resolution may be deteriorated.
If digital pulse is applied to a pin adjacent to the pin performing A/D conversion, desired
A/D conversion value may not be achieved due to the coupling noise. Do not apply pulse
to a pin adjacent to the pin performing A/D conversion.
(7) AV REF0 pin
This pin inputs the A/D converter reference voltage.
It converts signals input to ANI0 to ANI7 into digital signals according to the voltage applied between AV REF0
and AV
SS
.
The current flowing in the series resistor string can be reduced by setting the voltage to be input to the AV
REF0
pin to AV SS level in standby mode.