One distinction between MCU's and PLC's is that PLC's "talk" directly to industrial equipment, and itn their language, e.g. switch closures, current loops, motor control signals of sufficient current to do useful work, while MCU's do not.

It's very likely that a ladder logic interpreter could be implemented in a MCU, even an 805x type, but there's a limited area of intersection of the two domains.

I've got a few AB, Toshiba, and Cutler Hammer PLC's lying on the floor right behind where I'm sititng at the moment, and, I guarantee, you'd not want to try to apply an 805x to the sort of job these guys were doing when they were employed. It would be a BIG job!

RE