PIC18F2450-I/ML【PDF 9/241 页】IC PIC MCU FLASH 8KX16 28QFN

106

XMEGA A [MANUAL]

8077I–AVR–11/2012

Reset System

9.1

Features

Reset the microcontroller and set it to initial state when a reset source goes active

Multiple reset sources that cover different situations

– Power-on reset

– External reset

– Watchdog reset

– Brownout reset

– PDI reset

– Software reset

Asynchronous operation

– No running system clock in the device is required for reset

Reset status register for reading the reset source from the application code

9.2

Overview

The reset system issues a microcontroller reset and sets the device to its initial state. This is for situations where

operation should not start or continue, such as when the microcontrollers operates below its power supply rating. If a

reset source goes active, the device enters and is kept in reset until all reset sources have released their reset. The I/O

pins are immediately tri-stated. The program counter is set to the reset vector location, and all I/O registers are set to

their initial values. The SRAM content is kept. However, if the device accesses the SRAM when a reset occurs, the

content of the accessed location can not be guaranteed.

After reset is released from all reset sources, the default oscillator is started and calibrated before the device starts

running from the reset vector address. By default, this is the lowest program memory address, 0, but it is possible to

move the reset vector to the lowest address in the boot section.

The reset functionality is asynchronous, and so no running system clock is required to reset the device. The software

reset feature makes it possible to issue a controlled system reset from the user software.

The reset status register has individual status flags for each reset source. It is cleared at power-on reset, and shows

which sources have issued a reset since the last power-on.

An overview of the reset system is shown in Figure 9-1 on page 107.

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