Understanding UART Serial Communication

With UART (Universal Asynchronous Receiver/Transmitter) and USART (Universal Synchronous Asynchronous Receiver/Transmitter), microcontroller communicate using two data lines called RX and TX. Rx is used for listening (receiving) to other sources like other chips or computers, and TX is used for talking (transmitting). The speed that the two devices are communicating must be the same in asynchronous mode since there is no clock line connected between them. If each device has a different speed (baud rate), then the two would not be able to communicate. In synchronous mode, the two devices are connected together by a wire that has a clock tick on it. One of the devices produces this clock on the clock line and the other device conforms to this clock frequency. Two way communication can actually happen one wire and this mode is called half duplex. The transmission takes turns with the receiving. Full duplex is where the communication happens on two lines and the communication can happen simultaneously. The communication that is sent from one device to another is sent as a data frame. The data frame consists of a start bit, data bits (i.e. 8-bit number), and one or two stop bits. The data frame may or may not include a parity bit. The parity bit is a way for the microcontroller to determine if the data is valid or not. If something happened to the data on the way to the receiving end, the parity bit will give a clue to this error.