In a serial interface, the data is sent 1 bit after the other on a single wire. Serial data is classified as being either synchronous or asynchronous. Synchronous data require that the data bytes be sent as group in a “package”. It is employed in advanced communication systems that move a lot of data. Asynchronous data transfer is the most commonly used but slower type of serial transfer and allows for individual bytes to be sent when required.
Since data always exist in a parallel form inside the computer, it must be converted to serial data before coming out the serial port. This is achieved with a special parallel-to-serial converter IC called a universal asynchronous receiver transmitter (UART). On the other end of the line, a receiver must convert the serial data back into parallel data, which is done with another UART. This is illustrated in the figure below:
Serial Data Format
The figure below shows the standard format for asynchronous serial data:
First, a start bit is sent, then the data (LSB first, in this case, the LSB is 0), then a parity-error checking bit, and finally the stop bit(s). Some variation is permitted to this format, but both transmitter and receiver must use the same format.
Also read: Features of Hart Communication Protocol
