ABB TU891Z 3BSC840220R1 Module Termination Unit f. non Intrinsic Safety Applications. 3x9 signal terminals. G3 Compliant. The MTU distributes the ModuleBus to the I/O module and to the next MTU. It also generates the correct address to the I/O module by shifting the outgoing position signals to the next MTU. Model: TU891Z Product ID: 3BSC840220R1 Categories: S800 I/O Brand: ABB ABB S800 I/O is a comprehensive, distributed and modular process I/O system that communicates with parent controllers and PLCs over industry-standard fieldbus technology and therefore can be used with a wide range of process controllers from ABB and other vendors.