The RTS flow control logic is linked to the programmable receive FIFO watermark levels. When RTS flow control is enabled, the UARTx_RTS_b is asserted until the receive FIFO is filled up to the watermark level. When the receive FIFO watermark level is reached, the UARTx_RTS_b signal is deasserted, indicating that there is no more room to receive any more data. The transmission of data is expected to cease after the current character has been transmitted.
The UARTx_RTS_b signal is reasserted when data has been read out of the receive FIFO so that it is filled to less than the watermark level. If RTS flow control is disabled and the UART is still enabled, then data is received until the receive FIFO is full, or no more data is transmitted to it.