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Get additional one byte of value 0 for i.mx6ull UART8 as RS485

Question asked by lonsn on Apr 25, 2020
Latest reply on May 5, 2020 by Wigros Sun

In a custom i.mx6ull board, we use UART8 as RS485 interface. Data sent is OK, however when we open this port the rs485 application will read one byte data with 0(no data is sent from other rs485 endpoint in this bus). After that we will get normal correct rs485 data. For other UART/RS485 port in the same board, it works fine without this problem.

DTS file as below:

pinctrl_uart8dce: uart8dcegrp {
fsl,pins = <
MX6UL_PAD_LCD_DATA20__UART8_DCE_TX 0x1b0b1
MX6UL_PAD_LCD_DATA21__UART8_DCE_RX 0x1b0b1
MX6UL_PAD_LCD_DATA04__UART8_DCE_CTS 0x1b0b1 /* RS485 RE/DE */
MX6UL_PAD_LCD_DATA05__UART8_DCE_RTS 0x1b0b1
>;
};

What's the root cause?

Outcomes