RL78/F13, F14 CHAPTER 12 A/D CONVERTER
R01UH0368EJ0210 Rev.2.10 703
Dec 10, 2015
12.2 Configuration of A/D Converter
The A/D converter includes the following hardware.
(1) ANI0 to ANI23 (V
DD
) and ANI24 to ANI30 (EV
DD
) pins
These are the analog input pins of the twenty 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.
Caution If the supply setting other than AVREFP, AVREFM is used as the reference voltage of the A/D converter,
the conversion accuracy decreases. In addition, since the EV
DD
system analog pins have lower
accuracy than the V
DD
system analog pins, the V
DD
analog pins should be used for highly accurate
conversion.
(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
This 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 AV
REF)
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 AV
REF), 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 AV
REF)
Bit 9 = 1: (3/4 AVREF)
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 ï‚£ 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.
Remark AV
REF: The + side reference voltage of the A/D converter. This can be selected from AVREFP, the internal
reference voltage (1.45 V), and V
DD.
(4) Comparison voltage generator
The comparison voltage generator generates the comparison voltage input from an analog input pin.
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