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A project log for RV Rooftop A/C MPU Replacement

This project chronicles the successes, and frustrations to defeating the securities put in place by RV appliance manufacturers.

Daniel RosemanDaniel Roseman 08/06/2014 at 16:140 Comments

So, a little primer on the Motorola MCU on this main board. This is an 8-bit 8MHz 5v MCU with 4kb Flash designed by Motorola and built by Freescale Semiconductors. Four of it's input pins are 8-bit A/D converters and has 12 GPIO pins overall. This is a great MCU for professionals and tinkerers alike, as long as you have the proper hardware to program it in the first place.

More important to me in this dive down the rabbit hole, is that it has a security register. Once set, the end user CANNOT read flash contents without wiping it first... Meaning you can reset the MCU to zero but you cannot modify the original code. Since I don't have the equipment to identify whether or not that register had been set, I must assume it had been.

So, I have two options. Buy more equipment that we really can't afford in order to learn then hopefully reprogram an MCU. Or spend a fraction of that investment on a ready-to-program arduino...

Decisions... decisions...

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