SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
Two XOFF1 characters are transmitted when the RX FIFO passes the trigger level programmed by UART_TCR[3-0] RX_FIFO_TRIG_HALT. As soon as the RX FIFO reaches the trigger level programmed by UART_TCR[7-4] RX_FIFO_TRIG_START, two XON1 characters are sent, so the data transfer recovers.
If software flow control is disabled after an XOFF character is sent, the module transmits XON characters automatically to enable normal transmission.
The transmission of XOFF(s)/XON(s) follows the same protocol as transmission of an ordinary byte from the TX FIFO. This means that even if the word length is 5, 6, or 7 characters, the 5, 6, or 7 LSBs of XOFF1/2 and XON1/2 are transmitted. The 5, 6, or 7 bits of a character are seldom transmitted, but this function is included to maintain compatibility with earlier designs.
It is assumed that software flow control and hardware flow control are never enabled simultaneously.