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RS485 communication not working baud rate below 4800

shammi kaplesh
Expert 1475 points

I am using am335x based customized board and using RS485 , but Rs-485 communication is not working if the baud rate is below 4800.

  • 0
    TI__Guru**** 393215 points

    Please post the Linux version you are using.

  • 0 in reply to Biser Gatchev-XID
    Expert 1475 points

    i am using linux 3.2 kernel, above 4800 baud rate everything is working fine

  • 0 in reply to shammi kaplesh
    TI__Guru**** 161600 points

    Hi,

    Which baud rates are you trying to use?

    Have in mind that linux calculates the uart divisor using the following function:
    serial_omap_get_divisor(struct uart_port *port, unsigned int baud)
    {
        unsigned int divisor;

        if (baud > OMAP_MODE13X_SPEED && baud != 3000000)
            divisor = 13;
        else
            divisor = 16;
        return port->uartclk/(baud * divisor);
    }

    Where uartclk is defined in arch/arm/mach-omap2/serial.c:
    omap_up.uartclk = OMAP24XX_BASE_BAUD * 16;

    And OMAP24XX_BASE_BAUD & OMAP_MODE13x_SPEED are defined in arch/arm/plat-omap/include/plat/omap-serial.h:
    #define OMAP_MODE13X_SPEED 230400
    & arch/arm/plat-omap/include/plat/serial.h:
    #define OMAP24XX_BASE_BAUD (48000000/16)

    Setup this way omap serial driver supports ONLY the baud rates listed in Table 19-6. UART Mode Baud and Error Rates of AM335x TRM.

    Best Regards,
    Yordan