With serial interfaces, the data bits are transmitted serially, i.e. one after the other. In contrast to the parallel interface, only two data lines are available for transmit data( TxD) and receive data( RxD). The other lines are control and signal lines. Inpersonalcomputers( PC), the serial COM port is used to connectprinters, computer mouse or other peripheral devices.
Transmission through the serial port can be synchronous or asynchronous. Synchronous transmission involves the transmission of control signals over separate lines. In asynchronous transmission, the frame consists of the start bit followed by the data bits and the stop bit. Parity bits can be transmitted before the stop bit.
In addition to the older serial interfaces, there are the DIN interface or the PS/2 interface for the keyboard or computer mouse in personal computers, as well as the fast serial interconnect connections such as FireWire, 1394, the USB interface and the Serial Attached SCSI( SAS) for other peripheral devices. In addition, Ethernet, HDMI, the Digital Visual Interface( DVI) and the fieldbus interfaces operate serially. Data transmission can be simplex, half- duplex or duplex.