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CHAPTER 11 10-BIT A/D CONVERTER (
(6)
Noise prevention
To maintain a resolution of 10 bits, watch for noise to the AV
output impedance of the analog input source, the larger the effect by noise. To reduce noise, attach an
external capacitor to the relevant pins as shown in Figure 11-10.
C = 100 to 1,000 pF
(7)
ANI0 to ANI5
The analog input pins (ANI0 to ANI5) are alternate-function pins. They are also used as port pins (P60 to
P65).
If any of ANI0 to ANI5 has been selected for A/D conversion, do not execute input instructions for the ports;
otherwise the conversion resolution may be reduced.
If a digital pulse is applied to a pin adjacent to the analog input pins during A/D conversion, coupling noise
may occur that prevents an A/D conversion result from being obtained as expected. Avoid applying a digital
pulse to pins adjacent to the analog input pins during A/D conversion.
(8)
Interrupt request flag (ADIF0)
Changing the contents of A/D converter mode register 0 (ADM0) does not clear the interrupt request flag
(ADIF0).
If the analog input pins are changed during A/D conversion, therefore, the A/D conversion result and the
conversion end interrupt request flag may reflect the previous analog input immediately before writing to
ADM0 occurs. In this case, ADIF0 may already be set if it is read-accessed immediately after ADM0 is write-
accessed, even when A/D conversion has not been completed for the new analog input.
In addition, when A/D conversion is restarted, ADIF0 must be cleared beforehand.
212
µ
PD789436 AND 789456 SUBSERIES)
Figure 11-10. Analog Input Pin Treatment
If noise not lower than AV
AV
SS
the voltage at the pin by attaching a diode with
a small V
V
AV
AV
V
User's Manual U15075EJ2V1UD
and ANI0 to ANI5 pins. The higher the
DD
or not higher than
DD
is likely to come to the AV
DD
(0.3 V or lower).
F
DD
DD
SS
SS
pin, clamp
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