Differentiate between asynchronous and synchronous types of serial communication.
Serial data communication uses two fundamental types, asynchronous andsynchronous. With synchronous communications, two devices initially synchronize themselves to each other, and then persistently send characters to stay in sync. Even when data isn't really being sent, a constant flow of bits allows each device to know where other is at any given time. That is, every character which is sent is either actual data or an idle character.
Asynchronous means 'no synchronization' and thus doesn't require receiving and sending idle characters. Though the beginning and end of each byte of data should be identified by start and stop bits. Start bit indicates when data byte is about to begin and the stop bit signals when it ends. Requirement to send these extra two bits causes asynchronous communication to be slightly slower than synchronous although it has the advantage that processor doesn't have to deal with the additional idle characters.