The RX and TX FIFOs are each 128-bytes deep. Software reads and writes these FIFOs using the data port registers RX_data and TX_data.
RXFIFO
If the controller hardware attempts to push data into a full RXFIFO, the data is lost and the sticky overflow interrupt flag is set. No data is added to a full RXFIFO. Software writes a 1 to the interrupt to clear the ISR [RX_OVERFLOW] bit.
TXFIFO
If software attempts to write data into a full TXFIFO, the write is ignored. No data is added to a full TXFIFO. The ISR [TX_FIFO_full] bit is asserted until the TXFIFO is read and the TXFIFO is no longer full. If the TXFIFO overflows, the sticky [RX_OVERFLOW] bit is set = 1.