What is the difference between synchronous and asynchronous devices?
For asynchronous device, each data byte is framed by housekeeping bits. These bits provide the synchronization to the receiving facility each time when it receives data byte. Two wires (“signal” and “ground”) are enough to transmit the data. A part of data can come anytime. Asynchronous mode appeared together with the telegraphy and is successfully used up to nowadays. During the synchronous mode either data are accompanied by the special clock signal by the separate wire, or they are encoding so as clock rate could be extracted from the receiving data. In both cases each data bit is connected to the clock signal and it comes in strictly determined time.
