SPRUIM2H May 2020 – October 2023 AM2431 , AM2432 , AM2434 , AM6411 , AM6412 , AM6421 , AM6422 , AM6441 , AM6442
When software flow control operation is enabled, the UART compares incoming data with XOFF1/2 programmed characters (in certain cases, XOFF1 and XOFF2 must be received sequentially). When the correct XOFF characters are received, transmission stops after transmission of the current character completes. Detection of XOFF also sets the UART_IIR_UART[4] bit (if enabled by UART_IER_UART[5]) and causes the interrupt line to go low.
To resume transmission, an XON1/2 character must be received (in certain cases, XON1 and XON2 must be received sequentially). When the correct XON characters are received, the UART_IIR_UART[4] bit is cleared and the XOFF interrupt disappears.
When a parity, framing, or break error occurs while receiving a software flow control character, this character is treated as normal data and is written to the RX FIFO.
When XON-any and special character detect are disabled and software flow control is enabled, no valid XON or XOFF characters are written to the RX FIFO. For example, when UART_EFR[1-0] = 0x2, if XON1 and XOFF1 characters are received, they are not written to the RX FIFO.
When pairs of software flow characters are programmed to be received sequentially (UART_EFR[1-0] = 0x3), the software flow characters are not written to the RX FIFO if they are received sequentially. However, received XON1/XOFF1 characters must be written to the RX FIFO if the subsequent character is not XON2/XOFF2.