Programmable logic controllers (PLCs) are extensively used in industry to perform automation tasks, with manufacturers offering a variety of PLCs that differ in functions, program memories, and the number of inputsoutputs (IO). Not surprisingly, the design and implementation of these PLCs have long been a secret of manufacturers. Unveiling the mysteries of PLC technology, Building a Programmable Logic Controller with PIC16F648A Microcontroller explains how to design and use a PIC16F648A-microcontroller-based PLC.