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CHAPTER 11 A/D CONVERTER
User
’
s Manual U15017EJ2V0UD
11.5 Notes on A/D Converter
(1) Current consumption in standby mode
The A/D converter is stopped in the standby mode. At this time, the current consumption can be reduced by
stopping the conversion (by clearing bit 7 (ADCS) of the A/D converter mode register (ADM) to 0).
Figure 11-7 shows how the current consumption can be reduced in the standby mode.
Figure 11-7. Example of Reducing Current Consumption in Standby Mode
(2) Input range of ANI0 to ANI11
Make sure that the input voltages of ANI0 to ANI11 are within the rated range. If a voltage greater than AV
DD
or less than AV
SS
is input to a channel (even if it is within the absolute maximum rating range), the converted
value of the channel is undefined, and, in the worst case, the converted values of the other channels are
affected.
(3) Conflicting operation
<1>
Conflict between writing and reading A/D conversion result register (ADCR) on completion of conversion
Reading ADRC takes precedence. After ADCR has been read, a new conversion result is written to
ADCR.
Conflict between writing ADCR and input of external trigger signal on completion of conversion
An external trigger signal is not accepted during A/D conversion. Therefore, the external trigger signal
is not accepted while ADCR is written.
Conflict between writing ADCR and writing the A/D converter mode register (ADM) or writing the A/D
converter input select register (ADIS) on completion of conversion
Writing ADM or ADIS takes precedence. ADCR is not written. Nor is the conversion end interrupt request
signal (INTAD) generated.
<2>
<3>
(4) Noise measures
To maintain the 8-bit resolution, care must be exercised that no noise is superimposed on the AV
DD
and ANI0
to ANI11 pins. The higher the output impedance of the analog input source, the heavier the influence of noise.
To suppress noise, connecting external C as shown in Figure 11-8 is recommended.
AV
DD
AV
SS
P-ch
Series resistor string
ADCS