
CHAPTER 13 A/D CONVERTER
Preliminary User’s Manual U17790EJ1V0UD
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(10) Restriction for each mode
(a) To select the external trigger mode/timer trigger mode, set the high-speed conversion mode. Do not input
a trigger during stabilization time that is inserted once after the A/D conversion operation is enabled
(ADA0M0.ADA0CE bit = 1).
(b) In the following modes, write data to the A/D control register while A/D conversion is stopped (ADA0CE
bit = 0), and then enable the A/D conversion operation (ADA0CE bit = 1).
Normal conversion mode
One-shot select mode/one-shot scan mode of high-speed conversion mode
Remark
A/D control registers: ADA0M0, ADA0M2, ADA0S, ADA0PFM, and ADA0PFT registers
(11) Variation of A/D conversion results
The results of the A/D conversion may vary depending on the fluctuation of the supply voltage, or may be
affected by noise. To reduce the variation, take counteractive measures with the program such as averaging
the A/D conversion results.
(12) A/D conversion result hysteresis characteristics
The successive comparison type A/D converter holds the analog input voltage in the internal sample & hold
capacitor and then performs A/D conversion. After the A/D conversion has finished, the analog input voltage
remains in the internal sample & hold capacitor. As a result, the following phenomena may occur.
When the same channel is used for A/D conversions, if the voltage is higher or lower than the previous A/D
conversion, then hysteresis characteristics may appear where the conversion result is affected by the
previous value. Thus, even if the conversion is performed at the same potential, the result may vary.
When switching the analog input channel, hysteresis characteristics may appear where the conversion
result is affected by the previous channel value. This is because one A/D converter is used for the A/D
conversions. Thus, even if the conversion is performed at the same potential, the result may vary.