The APB UART is a simple Universal Asynchronous Receiver/Transmitter that supports 8-bit asynchronous serial communication without parity, and is fixed at one stop bit. The baud rate is fixed at 19200.

The UART also uses two FIFOs as buffers for both send and receive data. If the receive FIFO is empty and a read request is sent the UART will drive PREADY LOW and wait for data before continuing. If the transfer FIFO becomes full the UART will also drive PREADY LOW and wait for the FIFO to become not full before continuing.

The UART generates an interrupt, which is driven HIGH whenever there is data to be read on the receiving FIFO.