Section 3 Exception Handling; Overview; Reset; Reset Sequence - Renesas H8 Series Hardware Manual

3.1

Overview

Exception handling is performed in the H8/3644 Group when a reset or interrupt occurs. Table 3.1
shows the priorities of these two types of exception handling.
Table 3.1 Exception Handling Types and Priorities
Priority Exception Source
High

Reset

Interrupt
Low
3.2 Reset
3.2.1 Overview
A reset is the highest-priority exception. The internal state of the CPU and the registers of the on-
chip peripheral modules are initialized.
3.2.2

Reset Sequence

Reset by RES RES Pin: As soon as the RES pin goes low, all processing is stopped and the chip enters RES RES
the reset state.
To make sure the chip is reset properly, observe the following precautions.
• At power on: Hold the RES pin low until the clock pulse generator output stabilizes.
• Resetting during operation: Hold the RES pin low for at least 10 system clock cycles.
Reset exception handling begins when the RES pin is held low for a given period, then returned to
the high level.

Section 3 Exception Handling

Time of Start of Exception Handling
Exception handling starts as soon as the reset state is cleared
When an interrupt is requested, exception handling starts after
execution of the present instruction or the exception handling
in progress is completed
Section 3 Exception Handling
Rev. 6.00 Sep 12, 2006 page 59 of 526
REJ09B0326-0600