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APPENDIX
38C3 Group User’s Manual
3.3 Notes on use
3.3.5 Notes on A-D converter
(1)
Analog input pin
s 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.
q 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 conversion precision to be worse.
(2)
A-D converter power source pin
The AVSS pin is A-D converter power source pin. Regardless of using the A-D conversion function
or not, connect it as following :
AVSS : Connect to the VSS line.
q Reason
If the AVSS pin is opened, the microcomputer may have a failure because of noise or others.
(3)
Clock frequency during A-D conversion
The comparator consists of a capacity coupling, and a charge of the capacity will be lost if the clock
frequency is too low. Thus, make sure the following during an A-D conversion.
f(XIN) is 500 kHz or more.
Use clock divided by main clock (f(XIN)) as internal system clock.
Do not execute the STP instruction and WIT instruction.
3.3.6 Notes on reset circuit
(1)
Reset input voltage control
Make sure that the reset input voltage is 0.5 V or less for Vcc of 2.5 V (Note).
Perform switch to the high-speed mode when power source voltage is within 4.0 to 5.5 V.
Note: M version of mask ROM version is 2.2 V.
(2)
Countermeasure when RESET signal rise time is long
In case where the RESET signal rise time is long, connect a ceramic capacitor or others across the
RESET pin and the VSS pin. And use a 1000 pF or more capacitor for high frequency use. When
connecting the capacitor, note the following :
Make the length of the wiring which is connected to a capacitor as short as possible.
Be sure to verify the operation of application products on the user side.
q Reason
If the several nanosecond or several ten nanosecond impulse noise enters the RESET pin, it may
cause a microcomputer failure.