Universal Asynchronous Receiver Transmitter (UART)

The UART is one of the simplest methods of communication between an FPGA and another FPGA, a computer, or a microcontroller.

UART usually sends out information serially, one byte at a time. It is asynchronous, meaning that there is no clock signal forwarded with the data. Both the receiver and the transmitter have to share the same parameters/settings for UART to work:

Baud Rate (Bauds = bits per second)
Number of Data Bits (7 or 8)
Parity Bit (On or Off)
Stop Bits (1 or 2 or 3)
Flow Control (None or On or Hardware)

Parity checks if there are even/odd number of 1s in the data. This is done with a XOR operation.