This paper deals with digital data communication between electric drives and superimposed control levels. These applications require real-time capabilities, high performance and extreme reliability, which can only be guaranteed by fault tolerance and good diagnostics. Existing real-time communication systems lack fault tolerance. A description of a serial real-time communication system, which in contrast to existing systems achieves a high fault tolerance, as well as the ability of detecting the source and location of an error are introduced. The functionality of the system is kept even in events of faults.ETX