What is UART?

Universal Asynchronous receiver transmitter

• As name defines, it is asynchronous mode of communication which means communication between two devices is not dependent on any common signal ( no common clock pulse ) required to communicate.
• As it is Asynchronous mode of communication, hence " no master - no slave ".
• Independent clock of both the devices.
• It can be done only between 2 devices as this is not address mode communication.
• It follows RS232 standard which is given by EIA.
• RS232 voltage levels are 
1. -3 to -25 volts dc : logic 1
2.  3 to 25 volts dc   : logic 0
• While transmitting data, LSB is sent first.
• It follows full duplex mode of communication.
• It need one line to transmit the data and one line two receive the data, so basically 2 lines to full duplex.