HD6433713 datasheet(66/324 Pages) RENESAS

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Section 3 System Control

3.1 Overview

This section explains the reset state, exception handling, and system modes.

3.2 Exception Handling

Exception handling includes processing of reset exceptions and of interrupts. Table 3-1

summarizes the exception sources and their priorities. Reset exception handling has the highest

priority.

Table 3-1 Types of Exception Handling and Priorities

Priority

Exception Source

Timing for Start of Exception Handling

High

Reset

Reset exception handling starts as soon as RES pin changes

from low to high.

Interrupt

When interrupt request is made, interrupt exception handling

Low

starts after execution of present instruction is completed.

3.2.1 Reset

When the

RES pin goes low, all processing stops and the chip enters the reset state. The internal

state of the CPU and the registers of on-chip peripheral modules are initialized. The I bit of the

condition code register (CCR) is set, masking all interrupts.

As soon as the

RES pin goes from low to high, reset exception handling starts. The contents of

the reset vector address (H'0000 to H'0001) are read and loaded into the program counter (PC).

Then program execution starts from the address indicated in PC. Figure 3-1 shows the reset

sequence.

Notes: 1. To make sure a reset is carried out properly, when power is turned on the

RES pin

should be kept low for at least 20 ms after the rise of the power supply.

2. When resetting during operation, keep the

RES pin low for at least 10 system clock

cycles.

3. After a reset, if an interrupt were to be accepted before the stack pointer (SP: R7) was

initialized, PC and CCR would not be pushed onto the stack correctly, resulting in

program runaway. To prevent this, immediately after reset exception handling all

interrupts are masked. Programs should be coded to initialize the stack pointer before

clearing the interrupt mask. An even-numbered address must be set in SP. It is

recommended that programs start with an instruction initializing SP (e.g., MOV.W

#xx:16, SP).

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