Nowadays, the use of dependable systems is generalising, and diagnosis is an important step during their design . A diagnosis in early phases of the design cycle allows to save time and money. Fault injection can be used during the design process of the system, and using Hardware Description Languages, particularly VHDL, it is possible to accomplish this early diagnosis. During last years, the Time-Triggered Architecture (TTA) has emerged as a hard real-time fault-tolerant architecture for embedded systems. This novel architecture is gaining adepts mainly in the avionics and automotive industries ( x-by-wire ). The TTA implements a synchronous protocol with static scheduling that has been specifically targeted at hard real-time fault-tolerant distributed system. In this work, we present the study of the VHDL model of a communication controller based on the TTA, where a number of fault injection campaigns have been carried out. We comment the results produced and suggest some solutions to problems detected.