The ABB 3BSE086846R0001, also known as the TU891, is a compact Module Termination Unit (MTU) designed for the S800 I/O system. It serves as the connection interface for the CI840/CI840A PROFIBUS-DPV1 Fieldbus Communication Interface modules. The TU891 facilitates reliable communication and power distribution by providing a D-Sub 9-pin connector for the PROFIBUS-DP bus and power connections for the I/O module. It features a mechanical keying system to prevent the insertion of an incorrect I/O module, ensuring system integrity and safety. Its compact, DIN rail mountable design allows for efficient and organized installation within control cabinets.