Block Diagram Plc. The first two parts of this series evaluated ladder diagrams and textual programming as choices for models of computation. Like ladder logic function block diagrams are read left to right top to bottom.
Function block diagram programming is a language in which elements appear as blocks that are connected together resembling a circuit diagram. Fbds use data flows through feature blocks from left to right. It has three major unitssections.
Central processing unit cpu.
Cpu controls monitors and supervises all operation within plc. Cpu processes all the input data. This input module is connected with the cpu for the initial automated processes. Here we are concerned with the basic techniques involved in developing ladder and function block programs to represent basic switching operations involving the logic functions of and or exclusive or nand and nor as well as latching.