The abbreviation UART stands for Universal Asynchronous Receiver/Transmitter. It is a serial data interface with a defined speed. Regardless of the actual voltage level of the RS232 signals, these RS232/RS482 devices present signals to the microcontroller as a logical 0 or 1. This protocol sends data to the microcontroller serially, which means the data stream must be converted back to parallel (which is the function of the UART block in the microcontroller).
Data transfer via the USB bus is similar to RS232 with a some differences: USB is a faster transfer method, and to interface it with a microcontroller, we can use a USB to UART bridge, such as the FT232RL made by Future Technology Devices International LTD (FTDI) [1].
