RL78/G15 CHAPTER 10 A/D CONVERTER
R01UH0959EJ0110 Rev.1.10 Page 318 of 765
Mar 7, 2023
10.2 Configuration of A/D Converter
The A/D converter includes the following hardware.
1) ANI0 to ANI10
Note 1
These are the analog input pins of the 11 channels of the 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.
In addition to the voltages on analog input pins from ANI0 to ANI10, the internal reference voltage (0.815 (typ.)) can be
selected as the target of conversion by the A/D converter.
Note 1. ANI0, ANI2, ANI3 for 8-pin products; ANI0 to ANI3 for 10-pin products; ANI0 to ANI6 for 16-pin products
2) Sample & hold circuit
The sample & hold circuit samples each of the analog input voltages sequentially sent from the input circuit, and sends
them to the A/D voltage comparator. This circuit also holds the sampled analog input voltage during A/D conversion.
3) A/D voltage comparator
The A/D voltage comparator compares the voltage generated from the voltage tap of the comparison voltage generator
with the analog input voltage. If the analog input voltage is found to be greater than the reference voltage (1/2 V
DD
) as a
result of the comparison, the most significant bit (MSB) of the successive approximation register (SAR) is set. If the
analog input voltage is less than the reference voltage (1/2 V
DD
), the MSB bit of the SAR is reset.
After that, bit 8 of the SAR register is automatically set, and the next comparison is made. The voltage tap of the
comparison voltage generator is selected by the value of bit 9, to which the result has been already set.
Bit 9 = 0: (1/4 V
DD
)
Bit 9 = 1: (3/4 V
DD
)
The voltage tap of the comparison voltage generator and the analog input voltage are compared and bit 8 of the SAR
register is manipulated according to the result of the comparison.
Analog input voltage ≥ Voltage tap of comparison voltage generator: Bit 8 = 1
Analog input voltage ≤ Voltage tap of comparison voltage generator: Bit 8 = 0
Comparison is continued like this to bit 0 of the SAR register.
When performing A/D conversion at a resolution of 8 bits, the comparison continues until bit 2 of the SAR register.
4) Comparison voltage generator
The comparison voltage generator generates the comparison voltage input from an analog input pin.
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