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CHAPTER 12 A/D CONVERTER
User’s Manual U19780EJ2V0UD
350
12.6 Cautions for A/D Converter
(1) Operating current in STOP mode
Shift to STOP mode after stopping the A/D converter (by setting bit 7 (ADCS) of the A/D converter mode register
(ADM) to 0). The operating current can be reduced by setting bit 0 (ADCE) of the A/D converter mode register (ADM)
to 0 at the same time.
When using the A/D converter in normal mode 2 (LV1 = 0, LV0 = 1) or low-voltage mode (LV1 = 1, LV0 = 0), be sure
to clear bit 1 (VRGV) of the analog reference voltage control register (ADVRC) to 0 before shifting to STOP mode.
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 ANI6, ANI8 to ANI11, and ANI15
Observe the rated range of the ANI0 to ANI6, ANI8 to ANI11, and ANI15 input voltage. If a voltage of AV
DD
or higher
and AV
SS
or lower (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 12-bit resolution, attention must be paid to noise input to the AV
REF,
ANI0 to ANI6, ANI8 to ANI11,
and ANI15 pins .
<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 12-25 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.
Remark
78K0/KB2-A: ANI0 to ANI5, ANI8 to ANI11
78K0/KC2-A: ANI0 to ANI6, ANI8 to ANI11, ANI15