Interbus-S is an open architecture, serial bus, mater–slave type fieldbus communication system that operates in an active ring topology. It consists of one master and up to 511 slave devices. Each slave has an input and an output connector. It was developed by Phoenix Contact in 1984 to interchange data between control systems such as personal computers (PCs), programmable logic controllers (PLCs), and distributed input/output (I/O) modules that communicate with sensors/actuators.
A maximum of 4096 digital I/O points for a maximum distance of 400 m can be connected via this network. These points can be updated in 14 ms by employing a variable frame transfer protocol. This time can further be reduced by employing fewer I/Os. The data transfer rate on this bus is 500 kbps. The basic scheme of process control via Interbus is shown in Figure.
A bus cycle begins with the master passing a bit stream to the first slave. The first slave then transfers the same to the second slave in the ring, and at the same time data from the first slave is transferred to the master.