ABB · TU840 ABB TU840 Redundant Optical ModuleBus Modem Termination Unit ABB TU840 passive MTU for redundant TB840/TB840A Optical ModuleBus modem configuration with dual electrical ModuleBus, redundant I/O and 24 V DC input. Type Redundant modem termination unit System ABB S800 I/O / Optical ModuleBus Focus Redundant TB840/TB840A and I/O Brand ABB TU840 availability, lead time and order review Send RFQ Product Introduction TU840 is the passive S800 I/O termination unit for a