Programmable Logic Controllers (PLC) have been extensively used in industry for the past five-six decades. PLC manufacturers offer different PLCs in terms of functions, program memories, and the number of inputs/outputs (I/O), ranging from a few to thousands of I/Os. The design and implementation of PLCs have long been a secret of the PLC manufacturers. As a microprocessor based technology, the functionality of a PLC is well-known from the end-user (programmer) point of view, but by now no serious work has been reported to describe a microprocessor/microcontroller based implementation of a PLC.
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