7220 Datasheet, PDF (227/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
6.3 Notes on use
6.3.6 Notes on A-D comparator
(1) Signal source impedance for analog input
Make the signal source impedance for analog input low, or equip an analog input pin with an external
capacitor of 0.01 µF to 1 µF. 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.
(2) Note during an 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 comparison.
qf(XIN) is 500 kHz or more
qDo not execute the STP instruction and WIT instruction
6.3.7 Note on RESET pin
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 :
qMake the length of the wiring which is connected to a capacitor as short as possible.
qBe sure to check the operation of application products on the user side.
Reason
______
If the several nanosecond or several ten nanosecond impulse noise enters the RESET pin, it may cause
a microcomputer failure.
6-8
7220 Group User’s Manual