I know PLC ladder diagram programming, it is fun and too easy compared to C or assembly.
I once replaced a small plc with a single chip microcontroller, a couple of optocouplers and couple of darlingtons for outputs, The PLC timing resolution was something like 10msec while in my microcontroller board i managed to get the timing within usec resolution making the machine produce irrigation pipes with extreme accuracy. It has been working trouble free for over 2 years producing milions of pipes.
The beauty about ladder diagrams is that non technical people can program it and understand it easily. It is something like visual programming.
Regards
mahmood