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

11.2 Configuration of A/D Converter

The A/D converter includes the following hardware.
Registers
(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 by the analog input channel specification
register (ADS) can be used as input port pins.
(2) Sample & hold circuit
The sample & hold circuit samples the input signal of the analog input pin selected by the selector when A/D
conversion is started, and holds the sampled analog input voltage value during A/D conversion.
(3) Series resistor string
The series resistor string is connected between AV
the analog input signal.
(4) Voltage comparator
The voltage comparator compares the sampled analog input voltage and the output voltage of the series resistor
string.
(5) Successive approximation register (SAR)
This register compares the sampled analog voltage and the voltage of the series resistor string, and converts the
result, 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) A/D conversion result register (ADCR)
The result of A/D conversion is loaded from the successive approximation register (SAR) to this register each
time A/D conversion is completed, and the ADCR register holds the result of A/D conversion in its higher 10 bits
(the lower 6 bits are fixed to 0).
(7) Controller
When A/D conversion has been completed or when the power-fail detection function is used, this controller
compares the result of A/D conversion (value of the ADCR register) and the value of the power-fail comparison
threshold register (PFT). It generates the interrupt INTAD only if a specified comparison condition is satisfied as
a result.
220
CHAPTER 11 A/D CONVERTER
Table 11-1. Registers of A/D Converter Used on Software
Item
Successive approximation register (SAR)
A/D conversion result register (ADCR)
A/D converter mode register (ADM)
Analog input channel specification register (ADS)
Power-fail comparison mode register (PFM)
Power-fail comparison threshold register (PFT)
User's Manual U16227EJ2V0UD
Configuration
and AV , and generates a voltage to be compared with
REF SS