Tech & Buying Guide

In industrial automation, programmable logic controllers (PLCs) serve as the core intelligence of modern factory automation and distributed control systems (DCS). Understanding how a PLC transitions between modes is vital for maintenance engineers. Typically, a PLC operates across four primary modes: Run, Stop, Start-Up, and Hold. When power is applied, the system immediately boots into Stop mode before initiating the Start-Up sequence. If the controller encounters a critical error during execution, it automatically reverts to Stop mode to prevent equipment damage. Therefore, monitoring these state transitions helps technicians maintain high system availability.