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Resetting MC9RS08KA during power transitions

Posted: 23 Jan 2008 ?? ?Print Version ?Bookmark and Share

Keywords:MCU? microcontroller devices? reset function? power transition?

A simple function such as resetting an MCU during the application or removal of power can cause many problems if not managed properly. Symptoms of an improperly managed reset during power transitions can range from a delay in MCU response after power-up to erratic, inconsistent behavior to total system failure.

This document covers the main issues relating to this problem and leads users of MC9RS08KA devices to a safe, reliable approach to transitioning power in an application.

Reset in its most basic function ensures the MCU starts or restarts executing software code in a controlled manner. This document covers situations related to resetting the MCU when power is applied and removed from the MCU such as power-on reset (POR) and low-voltage detect (LVD) reset. It also covers general system protection features such as computer operating properly (COP), illegal opcode detect (ILOP), and illegal address detect (ILAD). This application note summarizes all sources of reset (synchronous, asynchronous, internal and external) available within the MC9RS08KA MCU generated during power-up or power-down transitions. Furthermore, system issues in the event of power-down are discussed.

On the MC9RS08KA, the reset pin is input only. Also, there is limited visibility of the internal reset and clocking. Therefore, it is difficult to observe the exact clocking and timing of the various reset sequences. The purpose of the application note is to provide information on the range of timing for the various reset conditions.

In most applications, several of the reset sources can occur at the same time. The combination of these must be considered for the safe operation of the MCU application.

View the PDF document for more information.

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