CCS/TM4C1294NCPDT: UART TTL to RS 485 Protocol

Hi,

  What enable pin are you talking about? This post may help https://e2e.ti.com/support/microcontrollers/other/f/908/p/800573/2967482?tisearch=e2e-quicksearch&keymatch=rs485#2967482.

Hi Nagasai,

  GPIO is quite simple. You can reference the TivaWare hello, blinky or project0 to get some ideas on how to use the GPIO pin. Below is the code snippet from the blink example. 

#define USER_LED1  GPIO_PIN_0
#define USER_LED2  GPIO_PIN_1

//*****************************************************************************
//
// The error routine that is called if the driver library encounters an error.
//
//*****************************************************************************
#ifdef DEBUG
void
__error__(char *pcFilename, uint32_t ui32Line)
{
}
#endif

//*****************************************************************************
//
// Main 'C' Language entry point.  Toggle an LED using TivaWare.
//
//*****************************************************************************
int
main(void)
{
    uint32_t ui32SysClock;

    //
    // Run from the PLL at 120 MHz.
    //
    ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                       SYSCTL_OSC_MAIN |
                                       SYSCTL_USE_PLL |
                                       SYSCTL_CFG_VCO_480), 120000000);

    //
    // Enable and wait for the port to be ready for access
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPION);
    while(!SysCtlPeripheralReady(SYSCTL_PERIPH_GPION))
    {
    }

    //
    // Configure the GPIO port for the LED operation.
    //
    GPIOPinTypeGPIOOutput(GPIO_PORTN_BASE, (USER_LED1|USER_LED2));

    //
    // Loop Forever
    //
    while(1)
    {
        //
        // Turn on the LED
        //
        GPIOPinWrite(GPIO_PORTN_BASE, (USER_LED1|USER_LED2), USER_LED1);

        //
        // Delay for a bit
        //
        SysCtlDelay(ui32SysClock/6);

        //
        // Turn on the LED
        //
        GPIOPinWrite(GPIO_PORTN_BASE, (USER_LED1|USER_LED2), USER_LED2);

        //
        // Delay for a bit
        //
        SysCtlDelay(ui32SysClock/6);
    }
}

What is the purpose that you need the enable pin? Can you elaborate a bit? I don't know about your system design. If you simply need to use a GPIO as an enable pin then why wouldn't you enable the pin before start the UART transmission? Are you not calling the UARTCharPut to transmit data? I would have thought that you enable the pin before you call the UARTCharPut. As far as how far ahead the enable pin needs to be active before the UART transmission starts is timing question you need to find out yourself. 

 As far as I know the RS485 is a standard that specifies differential signaling on two lines rather than single-ended with a voltage referenced to ground like that of the UART. The difference is at the electrical level, not protocol level. See below.

https://www.electronicdesign.com/what-s-difference-between/what-s-difference-between-rs-232-and-rs-485-serial-interfaces

https://www.ftdichip.com/Support/Documents/TechnicalNotes/TN_111%20What%20is%20UART.pdf

Hi,

  First of all, you never mentioned you are doing a Ethernet to Serial application referencing enet_s2e. Please look for the UARTChaPut in the serial_task.c file if you are using the enet_s2e example. You need to play around to find the best place to activate your enable pin. I will strongly suggest you start with a simple UART example and know how it will work in your system and where would you place the enable pin before you venture to the s2e which is a much complicated application. Once you figure out how you will activate the enable pin relative to the UART transactions then you can later migrate to the s2e. You can find the UART examples in the TivaWare under <TivaWare_Install>/examples/boards/ek-tm4c1294xl/uart_echo.