Datasheet

V850ES/JG3 APPENDIX E LIST OF CAUTIONS
R01UH0015EJ0300 Rev.3.00 Page 849 of 870
Sep 30, 2010
(16/36)
Chapter
Classification
Function Details of
Function
Cautions Page
External trigger
mode
To select the external trigger mode, set the high-speed conversion mode. Do not
input a trigger during stabilization time that is inserted once after the A/D
conversion operation is enabled (ADA0M0.ADA0CE bit = 1).
p. 423
Timer trigger
mode
To select the timer trigger mode, set the high-speed conversion mode. Do not
input a trigger during stabilization time that is inserted once after the A/D
conversion operation is enabled (ADA0M0.ADA0CE bit = 1).
p. 424
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.
p. 434
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 AVSS (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.
p. 434
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.
p. 434
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.
p. 434
Soft
Interrupt request
flag (ADIF)
The interrupt request flag (ADIF) is not cleared even if the contents of the ADA0S
register are changed. If the analog input pin is changed during A/D conversion,
therefore, the result of converting the previously selected analog input signal may
be stored and the conversion end interrupt request flag may be set immediately
before the ADA0S register is rewritten. If the ADIF flag is read immediately after
the ADA0S register is rewritten, the ADIF flag may be set even though the A/D
conversion of the newly selected analog input pin has not been completed. When
A/D conversion is stopped, clear the ADIF flag before resuming conversion.
p. 435
Chapter 13
Hard
A/D
converter
AV
REF0 pin (a) The AVREF0 pin is used as the power supply pin of the A/D converter and also
supplies power to the alternate-function ports. In an application where a
backup power supply is used, be sure to supply the same voltage as V
DD to
the AV
REF0 pin as shown in Figure 13-15.
(b) The AV
REF0 pin is also used as the reference voltage pin of the A/D converter.
If the source supplying power to the AV
REF0 pin has a high impedance or if the
power supply has a low current supply capability, the reference voltage may
fluctuate due to the current that flows during conversion (especially,
immediately after the conversion operation enable bit ADA0CE has been set
to 1). As a result, the conversion accuracy may drop. To avoid this, it is
recommended to connect a capacitor across the AV
REF0 and AVSS pins to
suppress the reference voltage fluctuation as shown in Figure 13-15.
(c) If the source supplying power to the AV
REF0 pin has a high DC resistance (for
example, because of insertion of a diode), the voltage when conversion is
enabled may be lower than the voltage when conversion is stopped, because
of a voltage drop caused by the A/D conversion current.
p. 436