ST6208C datasheet(24/104 Pages) STMICROELECTRONICS

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ST6208C/ST6209C/ST6210C/ST6220C

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5.3 RESET

5.3.1 Introduction

The MCU can be reset in three ways:

A low pulse input on the RESET pin

Internal Watchdog reset

Internal Low Voltage Detector (LVD) reset

5.3.2 RESET Sequence

The basic RESET sequence consists of 3 main

phases:

Internal (watchdog or LVD) or external Reset

event

A delay of 2048 clock (fINT) cycles

RESET vector fetch

The reset delay allows the oscillator to stabilise

and ensures that recovery has taken place from

the Reset state.

The RESET vector fetch phase duration is 2 clock

cycles.

When a reset occurs:

– The stack is cleared

– The PC is loaded with the address of the Reset

vector. It is located in program ROM starting at

address 0FFEh.

A jump to the beginning of the user program must

be coded at this address.

– The interrupt flag is automatically set, so that the

CPU is in Non Maskable Interrupt mode. This

prevents the initialization routine from being in-

terrupted. The initialization routine should there-

fore be terminated by a RETI instruction, in order

to go back to normal mode.

Figure 13. RESET Sequence

VDD

RESET PIN

WATCHDOG

VIT+

VIT-

WATCHDOG UNDERFLOW

RESET

2048 CLOCK CYCLE (fINT) DELAY

LVD

RESET

INTERNAL

RUN

RESET

RUN

RESET

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