Datasheet

78K0/Ix2 CHAPTER 11 A/D CONVERTER
R01UH0010EJ0500 Rev.5.00 397
Feb 28, 2012
Figure 11-25. 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
AVSS
ANI0 to ANI8
V
SS
(5) ANI0/P20 to ANI7/P27 and ANI8/P70
<1> The analog input pins (ANI0 to ANI7 and ANI8) are also used as digital I/O port pins (P20 to P27 and P70).
When A/D conversion is performed with any of ANI0 to ANI7 and ANI8 selected, do not access P20 to P27 and
P70 while conversion is in progress; otherwise the conversion resolution may be degraded.
<2> To use the ANI0/P20 to ANI7/P27 and ANI8/P70 pins for digital I/O port, it is recommended to the furthest
ANI4/P24 pin from AV
REF. To use these pins as analog input, it is recommended to select a pin to use starting
with the closest pin to AV
SS.
<3> If a digital pulse is applied to the pins adjacent to the pins currently used for A/D conversion, the expected value
of the A/D conversion may not be obtained due to coupling noise. Therefore, do not apply a pulse to the pins
adjacent to the pin undergoing A/D conversion.
(6) Input impedance of ANI0 to ANI8 pins
This A/D converter charges a sampling capacitor for sampling during sampling time.
Therefore, only a leakage current flow when sampling is not in progress, and a current that charges the capacitor
flows during sampling. Consequently, the input impedance fluctuates depending on whether sampling is in progress,
and on the other states.
To make sure that sampling is effective, however, it is recommended to keep the output impedance of the analog
input source to within 1 k, and to connect a capacitor of about 100 pF to the ANI0 to ANI8 pins (refer to Figure 11-
25).
Remark A/D converter analog input pins differ depending on products.
 78K0/IY2: ANI0, ANI1, ANI3 to ANI5
 78K0/IA2: ANI0 to ANI5
 78K0/IB2: ANI0 to ANI8
<R>