
APPLICATION
2.6 A-D converter
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3822 GROUP USER’S MANUAL
2.6.8 Notes on use
When using the A-D converter, notes the following.
(1) Operating conditions for using A-D converter
Operate the A-D converter in the following conditions.
sThe comparator is composed of a capacitance coupling. If the oscillation frequency is low, the charge
will be lost. Accordingly, make sure that f(XIN) at least 500 kHz during A-D conversion.
Do not execute the STP instruction or WIT instruction during A-D conversion.
sWhen an external trigger is selected, the A-D conversion being executed is stopped by inputting a
falling signal to the ADT pin during A-D conversion, and A-D conversion is resumed.
sApply a voltage of 2 V–VCC to the reference voltage input pin VREF. Note that if the VREF value is
lowered, the accuracy degrades.
sApply the same voltage as the VSS pin to the analog power source voltage input pin AVSS.
sSet the port used as an analog input pin for the input mode.
(Corresponding bit of port P6 direction register (address 000D16) = “0”) (Note)
Note: The port P6 direction register cannot read out. Use the STA instruction or LDM instruction to
set the port P6 direction register.
sWhen not using the A-D converter, connect the A-D converter power source pin AVSS to VSS line
which is the analog system.
(2) Other notes
Make the signal source impedance for analog input low, or equip an analog input pin with an external
capacitor of 0.01
F to 1 F. Further, be sure to verify the operation of application products on the
user side.
<REASON>
An analog input pin includes the capacitor for analog voltage comparison. Accordingly, when signals
from signal source with high impedance are input to an analog input pin, charge and discharge noise
generates. This may cause the A-D comparison precision to be worse.