PLC vs Microcontroller
PLC (Programmable Logic Controller) is a system (much like a personal computer) with many inputs and outputs for modules to control 5/12/28vdc or 120/220vac or higher current devices too. Ladder Logic is the graphical language for PLC's. It takes some getting used to understand this but it is very common for Industrial / Electrical Engineers. On the other hand, microcontrollers such as PICS, Basic Stamps, etc. are just the controller chip "or brains" for a larger system such as a PLC or custom electronic device.