The ABB TB840A is a ModuleBus Modem designed for use with the ABB S800 I/O system and Advant Controller 31 series. This essential component serves as an interface to the optical ModuleBus, enabling communication over extended distances and providing galvanic isolation for enhanced system reliability. The TB840A connects directly to the CEX-Bus on the CPU module and provides an electrical ModuleBus interface. When paired with the TB810 or TB811 Optical Port Interface, it converts the electrical signals to optical signals for fiber optic transmission. Its robust, DIN-rail mountable design makes it ideal for demanding industrial automation environments.