HD6473837H Datasheet, PDF (80/562 Pages) Renesas Technology Corp – Hardware Manual

Section 3 Exception Handling
3.1 Overview
Exception handling is performed in the H8/3834 Series 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
High
Low
Exception Source
Reset
Interrupt
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
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
As soon as the RES pin goes low, all processing is stopped and the H8/3834 enters 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.
If the MD0 pin is at the high level, reset exception handling begins when the RES pin is held low
for a given period, then returned to the high level. If the MD0 pin is low, however, when the RES
pin is held low for a given period and then returned to high level, the reset is not cleared
immediately. First the MD0 pin must go from low to high, then after 8,192 clock cycles the reset
is cleared and reset exception handling begins.
63