9.2 Asynchronous Transmission

The drift of the receiver clock compared to the transmitter clock is usually small.

Thus, errors caused by the lack of synchronization can be avoided if shorter sequences of bits are communicated between the transmitter and receiver.

This strategy is adopted by asynchronous transmission techniques where data is divided into characters and transmitted one character at a time, usually in sequences of eight bits.

The time required to send each character will not be long enough for the accumulative clock drift to cause errors of interpretation at the receiver side.

The receiver is allowed to re-synchronize with the transmitter at the start of each character transmission.

This illustrated in Figure 9.2 where a stop bit of value 1 is transmitted after sending the first eight bits.

This allows for the receiver to re-synchronize with the transmitter before the sampling drift is long enough to start misinterpreting the signal received.

9.2 Asynchronous Transmission

Figure 9.2: Example of Asynchronous Transmission