CHAPTER 12 A/D CONVERTER
User’s Manual U16899EJ2V0UD
262
12.6 Cautions for A/D Converter
(1) Operating current in standby mode
The A/D converter stops operating in the standby mode. At this time, the operating current can be reduced by
clearing bit 7 (ADCS) of the A/D converter mode register (ADM) to 0 (see Figure 12-2).
(2) Input range of ANI0 to ANI7
Observe the rated range of the ANI0 to ANI7 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) write and ADCR read by instruction upon the end
of conversion
ADCR read has priority. After the read operation, the new conversion result is written to ADCR.
<2> Conflict between ADCR 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 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 ANI7.
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 12-19, to reduce noise.
Figure 12-19. Analog Input Pin Connection
Reference
voltage
input
C = 100 to 1,000 pF
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
AV
SS
V
SS
ANI0 to ANI7
Содержание MuPD78F0132H
Страница 2: ...User s Manual U16899EJ2V0UD 2 MEMO ...