Connection to bus via corresponding bus adapter. Digital I/O modules in rugged full metal housing to IP 67; protected against pressure, water and harsh industrial environments (e.g. conveyor belts, welding shops and similar). INTERBUS connected to Rugged Line modules via twisted pair cable or optical fibre with a transmission rate of 0.5 or 2 MBd. LED diagnostics directly on module; DO modules continuously monitor the quality of the transmission signal on the optical cable for S/A connection and use an automatic signal quality compensation function. Uniform and straightforward mounting on a mounting plate; defective modules can be replaced quickly (without the need for tools); coupler for the bus and infeed may also contain a copper/optic converter.