SN65HVD1477: Receiving Only Carriage Returns

Allan,

So the communication is fine until the terminal tries to interpret it? Is it possible that noise from the COM adapter is corrupting the signal? If the R waveform from the RS485 transceiver to the COM adapter looks good, I'm not sure what else it could be.

Regards,

Eric Hackett

I suspect the baud rate is wrong. Try sending something from the PC, and compare the bit lengths in the waveforms.

The communication is fine on D until it goes through the SN65HVD1477. The differential output on Y and Z appears to mess up the UART data being transmitted. 

Blue (R Pin), Red (D Pin), Gold (Y-Z Pins)

Below is the UART data from Channel B (Red).

Below is the UART data from the output,

The red and gold waveforms have the same shape. Nothing looks wrong.

I do not know why your oscilloscope is not able to decode the differential signal. Try changing the threshold to zero.

Check that the two +/- signals are not exchanged.

For some reason removing this code from my project affects the buad rate of UART on A0, and A1,

 //==============    SSI     ==============

    //
    // The SSI0 peripheral must be enabled for use.
    //
    //SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI1);
    //SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
    //SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);

    //
    // Configure the pin muxing for SSI0 functions on port A2, A3, A4, and A5.
    // This step is not necessary if your part does not support pin muxing.
    // TODO: change this to select the port/pin you are using.
    //
    //GPIOPinConfigure(GPIO_PE4_SSI1XDAT0);
    //GPIOPinConfigure(GPIO_PE5_SSI1XDAT1);
    //GPIOPinConfigure(GPIO_PB5_SSI1CLK);

    //
    // Configure the GPIO settings for the SSI pins.  This function also gives
    // control of these pins to the SSI hardware.
    //
    //GPIOPinTypeSSI(GPIO_PORTE_BASE, GPIO_PIN_5 | GPIO_PIN_4);
    //GPIOPinTypeSSI(GPIO_PORTB_BASE, GPIO_PIN_5);

    //
    // Configure and enable the SSI port for SPI master mode.  Use SSI0,
    // system clock supply, idle clock level low and active low clock in
    // freescale SPI mode, master mode, 1MHz SSI frequency, and 8-bit data.
    // For SPI mode, you can set the polarity of the SSI clock when the SSI
    // unit is idle.  You can also configure what clock edge you want to
    // capture data on.  Please reference the datasheet for more information on
    // the different SPI modes.
    //
//    uint32_t ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
//                                           SYSCTL_OSC_MAIN |
//                                           SYSCTL_USE_OSC), 25000000);

//    SSIConfigSetExpClk(SSI1_BASE, ui32SysClock, SSI_FRF_MOTO_MODE_0,
//                           SSI_MODE_MASTER, 1000000, 8);

    //
    // Enable the SSI1 module.
    //
    //SSIEnable(SSI1_BASE);

    //Chip select pin.
//    ROM_GPIOPinTypeGPIOOutput(GPIO_PORTL_BASE, GPIO_PIN_0);
//    MAP_GPIOPadConfigSet(GPIO_PORTL_BASE, GPIO_PIN_0, GPIO_STRENGTH_12MA,
//                                 GPIO_PIN_TYPE_STD);

Ask about that in the microcontrollers forum.

Thanks for the help here Clemens, as always. 

JA,

Let us know if there are any other questions related to the transceiver, otherwise I will be closing this thread.

Regards,

Eric Hackett