NEC V850ES/KE1+ User Manual page 386

(4) Measures against noise
To keep a resolution of 10 bits, be aware of noise on the AV
impedance of the analog input source, the greater the effect of noise. Therefore, it is recommended to
connect external capacitors as shown in Figure 13-8 to reduce noise.
Reference voltage input
C ≥ 0.1 F
(5) ANI0/P70 to ANI7/P77 pins
The analog input pins (ANI0 to ANI7) function alternately as input port pins (P70 to P77).
When performing A/D conversion by selecting any of the ANI0 to ANI7 pins, do not execute an input
instruction to port 7 during conversion. This may decrease the conversion resolution.
If digital pulses are applied to the pin adjacent to the pin subject to A/D conversion, the value of the A/D
conversion may differ from the expected value because of coupling noise. Therefore, do not apply pulses to
the pin adjacent to the pin subject to A/D conversion.
(6) Input impedance of AV
A series resistor string of tens of 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
voltage error.
386
CHAPTER 13 A/D CONVERTER
Figure 13-8. Handling of Analog Input Pins
μ
pin
REF0
User's Manual U16896EJ2V0UD
and ANI0 to ANI7 pins. The higher the output
REF0
If noise of AV or higher or AV
REF0
generated, clamp with a diode with a small V
AV
REF0
ANI0 to ANI7
AV
SS
V
SS
pin and AV
REF0
pin and AV pin, resulting in a large reference
REF0 SS
or lower could be
SS
(0.3 V or lower).
F
pin.
SS