Datasheet

V850ES/JG3 CHAPTER 13 A/D CONVERTER
R01UH0015EJ0300 Rev.3.00 Page 434 of 870
Sep 30, 2010
13.6 Cautions
(1) When A/D converter is not used
When the A/D converter is not used, the power consumption can be reduced by clearing the ADA0M0.ADA0CE bit
to 0.
(2) Input range of ANI0 to ANI11 pins
Input the voltage within the specified range to the ANI0 to ANI11 pins. If a voltage equal to or higher than AV
REF0 or
equal to or lower than AV
SS (even within the range of the absolute maximum ratings) is input to any of these pins,
the conversion value of that channel is undefined, and the conversion value of the other channels may also be
affected.
(3) Countermeasures against noise
To maintain the 10-bit resolution, the ANI0 to ANI11 pins must be effectively protected from noise. The influence of
noise increases as the output impedance of the analog input source becomes higher. To lower the noise,
connecting an external capacitor as shown in Figure 13-12 is recommended.
Figure 13-12. Processing of Analog Input Pin
AV REF0
V DD
V SS
AV SS
Clamp with a diode with a low V F (0.3 V or less)
if noise equal to or higher than AV
REF0 or equal
to or lower than AV
SS may be generated.
ANI0 to ANI11
(4) Alternate I/O
The analog input pins (ANI0 to ANI11) function alternately as port pins. When selecting one of the ANI0 to ANI11
pins to execute A/D conversion, do not execute an instruction to read an input port or write to an output port during
conversion as the conversion resolution may drop.
Also the conversion resolution may drop at the pins set as output port pins during A/D conversion if the output
current fluctuates due to the effect of the external circuit connected to the port pins.
If a digital pulse is applied to a pin adjacent to the pin whose input signal is being converted, the A/D conversion
value may not be as expected due to the influence of coupling noise. Therefore, do not apply a pulse to a pin
adjacent to the pin undergoing A/D conversion.