CHAPTER 9 A/D CONVERTERUser’s Manual U18172EJ2V0UD1649.6 Cautions for A/D Converter(1) Supply current in STOP modeTo satisfy the DC characteristics of supply current in STOP mode, clear bit 7 (ADCS) and bit 0 (ADCE) of the A/Dconverter mode register (ADM) to 0 before executing the STOP instruction.(2) Input range of ANI0 to ANI3Observe the rated range of the ANI0 to ANI3 input voltage. If a voltage of V DD or higher and V SS or lower (even inthe range of absolute maximum ratings) is input to an analog input channel, the converted value of that channelbecomes 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, ADCRH read byinstruction upon the end of conversionADCR, ADCRH read has priority. After the read operation, the new conversion result is written to ADCR,ADCRH.<2> Conflict between ADCR, ADCRH write and A/D converter mode register (ADM) write or analog inputchannel specification register (ADS) write upon the end of conversionADM or ADS write has priority. ADCR, ADCRH write is not performed, nor is the conversion end interruptsignal (INTAD) generated.(4) Noise countermeasuresTo maintain the 10-bit resolution, attention must be paid to noise input to the VDD pin and ANI0 to ANI3 pins.<1> Connect a capacitor with a low equivalent resistance and a high frequency response to the power supply.<2> Because the effect increases in proportion to the output impedance of the analog input source, it isrecommended that a capacitor be connected externally, as shown in Figure 9-19, to reduce noise.<3> Do not switch the A/D conversion function of the ANI0 to ANI3 pins to their alternate functions duringconversion.<4> The conversion accuracy can be improved by setting HALT mode immediately after the conversion starts.Figure 9-19. Analog Input Pin ConnectionReferencevoltageinputC = 0.01 to 0.1 FIf there is a possibility that noise equal to or higher than V DD orequal to or lower than V SS may enter, clamp with a diode with asmall V F value (0.3 V or lower).V DDV SSANI0 to ANI3μ
