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  • What kind of external reset and which five internal resets does the Motorola MC68HC08 series microcontroller have?

    * Question

    What kind of external reset and which five internal resets does the Motorola MC68HC08 series microcontroller have?

    * Answer

    The Motorola MC68HC08 series microcontroller, a popular choice in various embedded systems applications, offers both external and internal reset features to ensure reliable operation and recovery from various fault conditions. Here is a breakdown of the reset types:

    External Reset
    1. External Reset Pin (RESET):
    – This is the most common method of resetting the microcontroller. An external reset is typically triggered by applying a low signal to the reset pin. This is useful for initiating a reset from an external source, such as a manual push button or when the system needs to be restarted due to an external event.

    Internal Resets
    1. Power-on Reset (POR):
    – The Power-on Reset automatically resets the microcontroller when the power supply voltage rises above a certain threshold. This ensures that the microcontroller starts in a known state every time it is powered on.

    2. Low Voltage Detect Reset (LVD):
    – This reset occurs when the supply voltage falls below a preset threshold. It is designed to protect the microchip’s operations during low voltage conditions, preventing undefined behavior or corruption of data.

    3. Illegal Opcode Reset:
    – Triggered when the microcontroller encounters an undefined or illegal opcode. This helps in recovering from software errors that might cause the system to execute unintended operations.

    4. Clock Monitor Reset:
    – This reset is activated if the clock signal stops or operates outside of its expected parameters. It ensures that the microcontroller does not execute instructions without a stable clock, which is crucial for timing-sensitive applications.

    5. Computer Operating Properly (COP) Reset or Watchdog Timer:
    – Also known as a watchdog timer reset, this mechanism resets the microcontroller if the software fails to “kick” or refresh the watchdog timer within a predetermined interval. This is critical for detecting and recovering from software lock-ups or infinite loops.

    These reset mechanisms are vital for maintaining the integrity and reliability of systems based on the MC68HC08 microcontroller, providing multiple safeguards against various failure modes.


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