Enhancing Safety and Efficiency for Isolated PLC I/O Designs with SPI Daisy Chain

Abstract:
Programmable Logic Controllers have the difficult task of interfacing with dozens of input and output devices spread out across an industrial or manufacturing facility. The modularity of PLCs and the hazardous nature of the factory environment impose challenging requirements on the efficiency and safety capabilities of these input and output channels beyond the IEC 61131-2 specification for PLC design. This paper will introduce an architecture that utilizes SPI daisy chaining to combine up to 128 input channels or 128 output channels along with integral safety, robustness, and diagnostic features to enhance PLC I/O design.