UPD78F0138 NEC, UPD78F0138 Datasheet - Page 252

• Manufacturer Part Number: UPD78F0138
• Description: (UPD78xxxx) 8-Bit Single-Chip Microcontrollers
• Manufacturer: NEC

12.2 Configuration of A/D Converter
(1) ANI0 to ANI7 pins
(2) Sample & hold circuit
(3) Series resistor string
(4) Voltage comparator
(5) Successive approximation register (SAR)
(6) A/D conversion result register (ADCR)
(7) Controller
252
The A/D converter includes the following hardware.
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.
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.
The series resistor string is connected between AV
the analog input signal.
The voltage comparator compares the sampled analog input voltage and the output voltage of the series resistor
string.
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).
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).
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.
Registers
Item
Table 12-1. Registers of A/D Converter Used on Software
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)
CHAPTER 12 A/D CONVERTER
User’s Manual U16228EJ2V0UD
REF
and AV
Configuration
SS
, and generates a voltage to be compared with