57.7.11.5 TXEMPTY, TXRDY and RXRDY Behavior

FLEX_US_CSR.TXEMPTY, FLEX_US_CSR.TXRDY and FLEX_US_CSR.RXRDY flags display a specific behavior when FIFOs are enabled.

The TXEMPTY flag is cleared as long as there are characters in the Transmit FIFO or in the internal shift register. TXEMPTY is set when there are no characters in the Transmit FIFO and in the internal shift register.

TXRDY indicates if a data can be written in the Transmit FIFO. Thus the TXRDY flag is set as long as the Transmit FIFO can accept new data. See figure TXRDY in Single Data Mode and TXRDYM = 0.

RXRDY indicates if an unread data is present in the Receive FIFO. Thus the RXRDY flag is set as soon as one unread data is in the Receive FIFO. See figure RXRDY in Single Data Mode and RXRDYM = 0 below.

TXRDY and RXRDY behavior can be modified using the TXRDYM and RXRDYM fields in the USART FIFO Mode register (FLEX_US_FMR) .

See FLEX_US_FMR for the FIFO configuration.