In a serial port, the communication takes place through a single line or a circuit. The data is transferred one bit at a time from sender to receiver. The serial port takes 8, 16, or 32 parallel bits from the computer bus and converts it as an 8, 16, or 32 bit serial stream. The name serial communication comes from the fact that each bit of information is transferred in series from one location to another.
Serial communications are of two types: Synchronous and Asynchronous.
Synchronous: In this type, the sending and receiving ends of the communication are synchronized using a clock that precisely times the period separating each bit. By checking the clock the receiving end can determine if a bit is missing or if an extra bit (usually electrically induced) has been introduced in the stream.
Asynchronous: In this type, the bit stream is marked to help keep track of each bit. The start bit indicates the start of the data stream and the timing of each bit helps in finding the position of each bit. Here, timing is not an important aspect but the speed of the ports should be the same.
