The LS1028A SoC includes two DUARTs (UART1 and UART2) and six LPUARTs. RTS/CTS hardware flow control is supported only on LPUART1-LPUART6, not on the DUARTs (UART1 and UART2). They only provide TX and RX pins. For RS485 automatic direction control, you can use anyone of the LPUARTn_RTS pin.