HD6433636SW datasheet(71/418 Pages) RENESAS

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Section 3 Exception Handling

3.1

Overview

Exception handling is performed in the H8/3637S 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

Exception Source

Time of Start of Exception Handling

High

Reset

Exception handling starts as soon as the reset state is cleared

Low

Interrupt

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 H8/3637S Series 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.

• When an external clock or ceramic oscillator is used, also, at power on the RES pin must be

held low for the crystal oscillator oscillation stabilization time shown in table 14.3 in section

14, Electrical Characteristics.

• Resetting during operation: Hold the RES pin low for at least 18 system clock cycles.

Reset exception handling begins when the

RES pin is held low for a given period, then returned to

the high level. Reset exception handling takes place as follows.

• The CPU internal state and the registers of on-chip peripheral modules are initialized, with the

I bit of the condition code register (CCR) set to 1.

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