A modular electrical bus system for a valve manifold has a main communication module with a plurality of modular I/O units each having a plurality of I/O fittings being both electrically and mechanically connectable together via a bridge member connecting adjacent units and the main communication module. At least one of the modular I/O units is also mechanically separable from and maintains communication connection to the main communication module. One or both of the modular IO units and main communication module may have an alpha-numeric display.