The IOM441-S relay module is used to extend Bender devices, such as the EDS44x. For example, in the IOM441-S, alarm messages of the basic device can be converted into switching commands for the 12 relay outputs (N/O contacts). Communication between the two devices takes place via the Bender backbone bus (BB bus), which is mounted to the rear of the devices. The BB bus also provides the supply voltage for the IOM441-S.