This guide summarizes field-proven rules for AI/AO/DI/DO wiring, shows how to choose between NO/NC contacts under the fail-safe principle, and explains how to decode typical cable schedule entries. PLC and DCS control systems Wiring Diagrams for Digital Input (DI), Digital Output (DO), Analog Input (AI), and Analog Output (AO) signals. There are four types of inputs and outputs in PLC and DCS systems. Digital Input Pressure switches, level switches, temperature switches, flow switches, vibration switches, on-off feedback of valves, run indications of any. Welcome to the Principle Cabinet Design training module for the DCS800, ABB DC drives. If you need help navigating this module, please click the Help button in the top right-hand corner.