Cautions For A/D Converter - NEC 78K0 Series User Manual

13.6 Cautions for A/D Converter

(1) Operating current in STOP mode
The A/D converter stops operating in the STOP mode. At this time, the operating current can be reduced by
clearing bit 7 (ADCS) and bit 0 (ADCE) of the A/D converter mode register (ADM) to 0.
To restart from the standby status, clear bit 0 (ADIF) of interrupt request flag register 1L (IF1L) to 0 and start
operation.
(2) Input range of ANI0 to ANI7
Observe the rated range of the ANI0 to ANI7 input voltage. If a voltage of AV
(even 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
<1> Conflict between A/D conversion result register (ADCR, ADCRH) write and ADCR or ADCRH read by
instruction upon the end of conversion
ADCR or ADCRH read has priority. After the read operation, the new conversion result is written to ADCR
or ADCRH.
<2> Conflict between ADCR or ADCRH write and A/D converter mode register (ADM) write, analog input
channel specification register (ADS), or A/D port configuration register (ADPC) write upon the end of
conversion
ADM, ADS, or ADPC write has priority. ADCR or ADCRH write is not performed, nor is the conversion end
interrupt signal (INTAD) generated.
(4) Noise countermeasures
To maintain the 10-bit resolution, attention must be paid to noise input to the AV
<1> Connect a capacitor with a low equivalent resistance and a good frequency response to the power supply.
<2> The higher the output impedance of the analog input source, the greater the influence. To reduce the
noise, connecting external C as shown in Figure 13-20 is recommended.
<3> Do not switch these pins with other pins during conversion.
<4> The accuracy is improved if the HALT mode is set immediately after the start of conversion.
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CHAPTER 13 A/D CONVERTER
Preliminary User's Manual U17260EJ3V1UD
or higher and AV or lower
REF SS
pin and pins ANI0 to ANI7.
REF