Configuration Of A/D Converter - NEC 78K0 Series User Manual

13.2 Configuration of A/D Converter

The A/D converter includes the following hardware.
(1) ANI0 to ANI7 pins
These are the analog input pins of the 8-channel A/D converter. They input analog signals to be converted into
digital signals. Pins other than the one selected as the analog input pin can be used as I/O port pins.
(2) Sample & hold circuit
The sample & hold circuit samples the input voltage of the analog input pin selected by the selector when A/D
conversion is started, and holds the sampled voltage value during A/D conversion.
(3) Series resistor string
The series resistor string is connected between AV
the sampled voltage value.
(4) Voltage comparator
The voltage comparator compares the sampled voltage value and the output voltage of the series resistor string.
(5) Successive approximation register (SAR)
This register converts the result of comparison by the voltage comparator, starting from the most significant bit
(MSB).
When the voltage value is converted into a digital value down to the least significant bit (LSB) (end of A/D
conversion), the contents of the SAR register are transferred to the A/D conversion result register (ADCR).
(6) 10-bit A/D conversion result register (ADCR)
The A/D conversion result is loaded from the successive approximation register to this register each time A/D
conversion is completed, and the ADCR register holds the A/D conversion result in its higher 10 bits (the lower 6
bits are fixed to 0).
CHAPTER 13 A/D CONVERTER
Figure 13-2. Circuit Configuration of Series Resistor String
AV
REF
P-ch
AV
SS
Preliminary User's Manual U17260EJ3V1UD
and AV , and generates a voltage to be compared with
REF SS
ADCS
Series resistor string
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