EB413

Freescale Semiconductor, Inc. Order this document by EB413/D Motorola Semiconductor Engineering Bulletin EB413 Freescale Semiconductor, Inc... Resetting MCUs By Ross Mitchell MCU Applications Motorola Ltd. East Kilbride, Scotland Introduction A simple function such as reset can cause many problems since different applications impose very different conditions on the start up and power down of the microcontroller unit (MCU). This document covers the main issues relating to reset and aims to lead the user of the M68HC05 and M68HC11 devices to a safe a reliable approach for the application. Reset in its most basic function ensures that the MCU starts executing code in a controlled manner once power is applied. It may also be used to prevent the device running out of specification (often in conjunction with external devices) and can cause a system reset at the board level whenever the MCU has not executed the code in the expected way (watchdog). © Motorola, Inc., 1993, 2000 EB413 For More Information On This Product, Go to: www.freescale.com Freescale Semiconductor, Inc. Engineering Bulletin Factors which affect reset are: 1. External components attached to the RESET pin 2. Low-voltage reset (LVR) on chip 3. Power-on reset (POR) detection 4. System power-up sequence 5. Watchdog operation 6. Electrically erasable, programmable read-only memory (EEPROM) on chip Freescale Semiconductor, Inc... 7. Battery backup 8. Device controls to its own power off 9. Partial power loss 1...