Cautions For A/D Converter - NEC 78K0S/KA1+ Preliminary User's Manual

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10.6 Cautions for A/D Converter

(1) Operating current in standby mode
The A/D converter stops operating in the standby mode. At this time, the operating current can be reduced by
clearing bit 7 (ADCS) of the A/D converter mode register (ADM) to 0 (see Figure 10-3).
(2) Input range of ANI0 to ANI3
Observe the rated range of the ANI0 to ANI3 input voltage. If a voltage of AV
in the range of absolute maximum ratings) is input to an analog input channel, the converted value of that channel
becomes undefined. In addition, the converted values of the other channels may also be affected.
(3) Conflicting operations
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<1> Conflict between A/D conversion result register (ADCR, ADCRH) write and ADCR, ADCRH read by
<2> Conflict between ADCR, ADCRH write and A/D converter mode register (ADM) write or analog input
(4) Noise countermeasures
To maintain the 10-bit resolution, attention must be paid to noise input to the AV
Because the effect increases in proportion to the output impedance of the analog input source, it is recommended
that a capacitor be connected externally, as shown in Figure 10-20, to reduce noise.
Reference
voltage
C = 100 to 1,000 pF
instruction upon the end of conversion
ADCR, ADCRH read has priority. After the read operation, the new conversion result is written to ADCR,
ADCRH.
channel specification register (ADS) write upon the end of conversion
ADM or ADS write has priority. ADCR, ADCRH write is not performed, nor is the conversion end interrupt
signal (INTAD) generated.
Figure 10-20. Analog Input Pin Connection
input
CHAPTER 10 A/D CONVERTER
If there is a possibility that noise equal to or higher than AV
equal to or lower than V
small V value (0.3 V or lower).
F
AV
REF
ANI0 to ANI3
V
SS
Preliminary User's Manual U16898EJ1V0UD
or higher and V or lower (even
REF SS
pin and pins ANI0 to ANI3.
REF
may enter, clamp with a diode with a
SS
or
REF
169