CHAPTER 10 A/D CONVERTER
User’s Manual U17446EJ3V1UD
176
10.6 Cautions for A/D Converter
(1) Operating current in STOP mode
To satisfy the DC characteristics of the supply current in the STOP mode, clear bit 7 (ADCS) and bit 0 (ADCE) of
the A/D converter mode register (ADM) to 0 before executing the STOP instruction.
(2) Input range of ANI0 to ANI3
Observe the rated range of the ANI0 to ANI3 input voltage. If a voltage of AV
REF
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, ADCRH read by
instruction upon the end of conversion
ADCR, 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 input
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.
(4) Noise
countermeasures
To maintain the 10-bit resolution, attention must be paid to noise input to the AV
REF
pin and pins ANI0 to ANI3.
<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 is
recommended that a capacitor be connected externally, as shown in Figure 10-19, to reduce noise.
<3> Do not switch the A/D conversion function of the ANI0 to ANI3 pins to their alternate functions during
conversion.
<4> The conversion accuracy can be improved by setting HALT mode immediately after the conversion starts.
Figure 10-19. Analog Input Pin Connection
Reference
voltage
input
C = 0.01 to 0.1 F
If there is a possibility that noise equal to or higher than AV
REF
or
equal to or lower than AV
SS
may enter, clamp with a diode with a
small V
F
value (0.3 V or lower).
AV
REF
ANI0 to ANI3
μ
AV
SS
V
SS
<R>
Содержание 78K0S/KB1+
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