Hardware-Based Single-Clock-Cycle Edge Detector for a PLC Central Processing Unit

This article discusses edge detectors implemented in programmable logic controllers. The behaviors of different vendors' solutions are presented with pros and cons. The trigger functions defined in the IEC 61131-3 standard were analyzed for implementations. The main contribution of this paper is an idea for hardware acceleration of standard trigger functions that enables us to build single-clock-cycle edge detectors. Additionally, the structure for automatic edge detection on every input is shown. The structure with a synthesizable Verilog HDL description is presented. The comparison of the solution with vendor programmable logic controllers (PLCs) proves the effectiveness of the designed hardware-aided unit.