Hi Richard,

Before you conclude that µ-controllers will be cheaper that programmable logic controllers, consider the cost of designing, fabricating and assembling the circuit boards, and compare that result to, as one example, the offerings ay this link (http://www.tri-plc.com). I don't know if it would be cheaper, but it's certainly worth looking into.

On the other hand (I'm asking Erik this question), would it really be very difficult to use the bootloader to change the program in a µ-controller system?