RS485 with 9 data bits

[BergLoewe]

Hello,

what can I do for work with the UART with 9 data bits? I have the example "uart_echo_rs485". Here is the statement

Code: Select all

	 uart_config_t uart_config = {
        .baud_rate = BAUD_RATE,
        .data_bits = UART_DATA_8_BITS,
        .parity = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
        .rx_flow_ctrl_thresh = 122,
        .source_clk = UART_SCLK_APB,
    };

and I did change the .data_bits in

Code: Select all

	uart_config_t uart_config = { .baud_rate = BAUD_RATE,
			.data_bits = UART_DATA_BITS_MAX, 
			.parity = UART_PARITY_DISABLE, .stop_bits = UART_STOP_BITS_1,
			.flow_ctrl = UART_HW_FLOWCTRL_DISABLE, .rx_flow_ctrl_thresh = 122,
			.source_clk = UART_SCLK_APB, };

but this don't works.

[Scott.Bonomi]

I suggest you look up the definition of UART_DATA_BITS_MAX. Or set a log statement to print it. It appears to be a limit to a table not a functional number of bits.

[BergLoewe]

I did find this here
https://docs.espressif.com/projects/esp ... d_length_t

Here stays an option for 5, 6, 7, 8 and "max" data bits. I did hope, that "max" means 9 data bits.

[ESP_alisitsyn]

Hello @BergLoewe,

The UART does not support 9 data bits in the frame.
Each UART controller has the following features:
• Programmable baud rate
• 512 x 8-bit RAM shared by TX FIFOs and RX FIFOs of two UART controllers
• Full duplex asynchronous communication
• Automatic baud rate detection
• Data bits ranging from 5 to 8
• Stop bits whose length can be 1, 1.5, 2 bits
• Parity bits

However if you are going to use the Multidrop mode in RS485 communication the parity bit can be used to detect address. There is possibility to detect incorrect parity bit (UART_PARITY_ERR, UART_INTR_RS485_PARITY_ERR status bit) in the interrupt and handle it accordingly in the custom uart interrupt handler. Can it be useful for your project?