NEC 78K0S/KA1+ Preliminary User's Manual page 170

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(5) ANI0/P20 to ANI3/P23
<1> The analog input pins (ANI0 to ANI3) are also used as input port pins (P20 to P23).
When A/D conversion is performed with any of ANI0 to ANI3 selected, do not access port 2 while
conversion is in progress; otherwise the conversion resolution may be degraded.
<2> 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 ANI3 pins
In this A/D converter, the internal sampling capacitor is charged and sampling is performed for approx. one sixth
of the conversion time.
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Since only the leakage current flows other than during sampling and the current for charging the capacitor also
flows during sampling, the input impedance fluctuates and has no meaning.
To perform sufficient sampling, however, it is recommended to make the output impedance of the analog input
source 10 kΩ or lower, or attach a capacitor of around 100 pF to the ANI0 to ANI3 pins (see Figure 10-20).
(7) AV pin input impedance
REF
A series resistor string of several tens of 10 kΩ is connected between the AV
Therefore, if the output impedance of the reference voltage source is high, this will result in a series connection to
the series resistor string between the AV
170
CHAPTER 10 A/D CONVERTER
and V pins, resulting in a large reference voltage error.
REF SS
Preliminary User's Manual U16898EJ1V0UD
and V pins.
REF SS