Processing Of Analog Input Pin - NEC V850/SA1 mPD703015 Preliminary User's Manual

(4) Countermeasures against noise
To keep the resolution of 10 bits, prevent noise from being superimposed on the AV
pins. The higher the output impedance of the analog input source, the heavier the influence of noise. To lower
noise, connecting an external capacitor as shown in Figure 11-8 is recommended.
Reference voltage input
C = 100 to 1000 pF
(5) ANI0 through ANI11
The analog input (ANI0 through ANI11) pins are multiplexed with port pins.
To execute A/D conversion with any of ANI0 through ANI11 selected, do not execute an instruction that inputs
data to the port during conversion; otherwise, the resolution may drop.
If a digital pulse is applied to pins adjacent to the pin whose input signal is converted into a digital signal, the
expected A/D conversion result may not be obtained because of the influence of coupling noise. Therefore, do
not apply a pulse to the adjacent pins.
(6) Input impedance of AV
A series resistor string of about 15.5 kΩ (TYP.) is connected between the AV
If the output impedance of the reference voltage source is too high, the series resistor string between the AV
and AV pins are connected in parallel, increasing the error of the reference voltage.
SS
CHAPTER 11
Figure 11-8. Processing of Analog Input Pin
pin
REF
A/D CONVERTER
Clamp with diode with a low V
AV or lower than AV may be generated.
REF SS
AV
REF
V
DD
AV
DD
AV
SS
V
SS
and AV
REF
and ANI0 through ANI11
REF
(0.3 V MAX.) if noise higher than
F
pins.
SS
REF
315