UPD784938 Datasheet, PDF (405/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 16 A/D CONVERTER
Cautions 1. A capacitor should be connected between the analog input pins (ANI0 to ANI7) and AVSS, and
between the reference voltage input pin (AVREF1) and AVSS to prevent malfunction due to noise.
Be sure to connect the capacitor as closely to ANI0 through ANI7 and AVREF1 as possible.
Figure 16-2. Example of Capacitor Connection on A/D Converter Pins
Analog
input
100 to
500 pF
Reference
voltage input
µPD784938
ANI0 to ANI7
AVREF1
AVSS
2. A voltage outside the range AVSS to AVREF1 should not be applied to pins used as A/D converter
input pins. See 16.6 Cautions for details.
(1) Input circuit
The input circuit selects the analog input in accordance with the specification of the A/D converter mode register (ADM),
and sends the analog input to the sample & hold circuit according to the operation mode,
(2) Sample & hold circuit
The sample & hold circuit samples the analog inputs arriving sequentially one by one and holds the analog input in
the process of A/D conversion.
(3) Voltage comparator
The voltage comparator determines the voltage difference between the analog input and the series resistor string value
tap.
(4) Series resistor string
The series resistor string is used to generate voltages that match the analog inputs.
The series resistor string is connected between the A/D converter reference voltage pin (AVREF1) and the A/D converter
GND pin (AVSS). To provide 256 equal voltage steps between the two pins, it is made up of 255 equal resistors and
two resistors with half that resistance value.
The series resistor string voltage tap is selected by a tap selector controlled by the SAR successive approximation
register.
Preliminary User’s Manual U13987EJ1V0UM00
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