Analog Input Pin Disposition - NEC PD78052 User Manual

(3) Noise countermeasures
In order to maintain 8-bit resolution, attention must be paid to noise on pins AV
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 14-11 in order to reduce noise.
Reference
Voltage Input
C=100-1000 pF
(4) Pins ANI0/P10 to ANI7/P17
The analog input pins ANI0 to ANI7 also function as input/output port (PORT1) pins.
When A/D conversion is performed with any of pins ANI0 to ANI7 selected, be sure not to execute an input
instruction to PORT1 while conversion is in progress, as this may reduce the conversion resolution.
Also, if digital pulses are applied to a pin adjacent to the pin in the process of A/D conversion, the expected
A/D conversion value may not be obtainable due to coupling noise. Therefore, avoid applying pulses to pins
adjacent to the pin undergoing A/D conversion.
(5) AV pin input impedance
REF0
A series resistor string of approximately 10 k
Therefore, if the output impedance of the reference voltage source is high, this will result in parallel connection
to the series resistor string between the AV
error.
CHAPTER 14 A/D CONVERTER
Figure 14-11. Analog Input Pin Disposition
If there is possibility that noise whose
level is AV
clamp with a diode with a small V
V
DD
is connected between the AV
pin and the AV
REF0
REF0
or higher or AV or lower may enter,
REF0 SS
(0.3 V or less).
F
AV
REF0
ANI0-ANI7
V
DD
AV
DD
AV
SS
V
SS
REF0
pin, and there will be a large reference voltage
SS
and ANI0 to ANI7. Since
pin and the AV pin.
SS
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