Hardware manual

Microcomputer Technical Q&A
24
Q&A No.: QAH8S-021
Category: Exception Handling
Subject: Reset
Question
A reset time of at least 20 ms is specified. Does this also apply when an external clock is used?
Answer
No, this specification does not apply in the case of an external clock. When an external clock is
used, the reset time should be at least 500 µs. A reset of at least the length of the external clock
output settling delay time (t
DEXT
= 500 µs) is necessary to allow the clock output to stabilize (see
figure below).
EXTAL
V
CC
RES
t
DEXT
φ
Oscillation Settling Timing