1587 Synchronous and Asynchronous Communication Systems A. D. Reis Universidade da Beira Interior, Portugal Universidade de Aveiro, Portugal José F. Rocha Universidade de Aveiro, Portugal Atilio S. Gameiro Universidade de Aveiro, Portugal José P. Carvalho Universidade da Beira Interior Covilhã, Portugal S introduction This article talks generically about telecommunica- tion systems. A telecommunication system involves a transmitter, a transmission medium, and a receiver. The type of communication between the transmitter and the receiver can be the synchronous transmission mode whereas in the asynchronous case of 8/10=0.8 - > 80%. For this reason, the synchronous mode is more efficient in terms of transmission since all the bits are information, and there is no redundancy. Then for the same transmission bit rate, the synchronous system carries more information bits. The synchronous and the asynchronous systems