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I am struggling to understand how to work with UART interface between microcontrollers. I don't know if this happens because I can't understand how it works or because I manipulate it in a wrong way. In any case,I try to be hands on ,trying to understand how it works quickly and get the taste of it but so far I am unsuccessful.I have read several tutorials about the "theory" but I am having difficulties being hands-on.

Here is what I am trying to do: I have a MCU (CC1310 on a launchpad) with a UART port. I try to see if I can make this MCU talk to my PC first by sending some data. Later I need to make this MCU talk with another MCU.

First, I have to mention that this launchpad has a XDS 1100 Debugger linked to the computer via USB.There are some jumpers on the board with RX TX so I suppose this allows the XDS110 to act as FTDI converter USB to UART directly via a USB port (I also have a special cable from Prolific to probe signals without going through the debugger).

In Code Composer Studio, I have imported and built a project named uart_echo for the CC1310. I found this example in Ti Resources Explorer. I managed to build the project (as I didn't change anything and this code was written by Texas Instruments) and load it into the chip by using the debugging button.

The code in this file is the following:

    /*
 * Copyright (c) 2015-2016, Texas Instruments Incorporated
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * *  Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * *  Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * *  Neither the name of Texas Instruments Incorporated nor the names of
 *    its contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 *  ======== uartecho.c ========
 */

/* XDCtools Header files */
#include <xdc/std.h>
#include <xdc/runtime/System.h>

/* BIOS Header files */
#include <ti/sysbios/BIOS.h>
#include <ti/sysbios/knl/Task.h>

/* TI-RTOS Header files */
#include <ti/drivers/PIN.h>
#include <ti/drivers/UART.h>

/* Example/Board Header files */
#include "Board.h"

#include <stdint.h>

#define TASKSTACKSIZE     768

Task_Struct task0Struct;
Char task0Stack[TASKSTACKSIZE];

/* Global memory storage for a PIN_Config table */
static PIN_State ledPinState;

/*
 * Application LED pin configuration table:
 *   - All LEDs board LEDs are off.
 */
PIN_Config ledPinTable[] = {
    Board_LED1 | PIN_GPIO_OUTPUT_EN | PIN_GPIO_LOW | PIN_PUSHPULL | PIN_DRVSTR_MAX,
    Board_LED2 | PIN_GPIO_OUTPUT_EN | PIN_GPIO_LOW | PIN_PUSHPULL | PIN_DRVSTR_MAX,
    PIN_TERMINATE
};

/*
 *  ======== echoFxn ========
 *  Task for this function is created statically. See the project's .cfg file.
 */
Void echoFxn(UArg arg0, UArg arg1)
{
    char input;
    UART_Handle uart;
    UART_Params uartParams;
    const char echoPrompt[] = "\fEchoing characters:\r\n";

    /* Create a UART with data processing off. */
    UART_Params_init(&uartParams);
    uartParams.writeDataMode = UART_DATA_BINARY;
    uartParams.readDataMode = UART_DATA_BINARY;
    uartParams.readReturnMode = UART_RETURN_FULL;
    uartParams.readEcho = UART_ECHO_OFF;
    uartParams.baudRate = 9600;
    uart = UART_open(Board_UART0, &uartParams);

    if (uart == NULL) {
        System_abort("Error opening the UART");
    }

    UART_write(uart, echoPrompt, sizeof(echoPrompt));

    /* Loop forever echoing */
    while (1) {
        UART_read(uart, &input, 1);
        UART_write(uart, &input, 1);
    }
}

/*
 *  ======== main ========
 */
int main(void)
{
    PIN_Handle ledPinHandle;
    Task_Params taskParams;

    /* Call board init functions */
    Board_initGeneral();
    Board_initUART();

    /* Construct BIOS objects */
    Task_Params_init(&taskParams);
    taskParams.stackSize = TASKSTACKSIZE;
    taskParams.stack = &task0Stack;
    Task_construct(&task0Struct, (Task_FuncPtr)echoFxn, &taskParams, NULL);

    /* Open LED pins */
    ledPinHandle = PIN_open(&ledPinState, ledPinTable);
    if(!ledPinHandle) {
        System_abort("Error initializing board LED pins\n");
    }

    PIN_setOutputValue(ledPinHandle, Board_LED1, 1);

    /* This example has logging and many other debug capabilities enabled */
    System_printf("This example does not attempt to minimize code or data "
                  "footprint\n");
    System_flush();

    System_printf("Starting the UART Echo example\nSystem provider is set to "
                  "SysMin. Halt the target to view any SysMin contents in "
                  "ROV.\n");
    /* SysMin will only print to the console when you call flush or exit */
    System_flush();

    /* Start BIOS */
    BIOS_start();

    return (0);
}

Then I used PuTTY. I looked at my COM port in Windows and found out :

Class Application / USER UART : COM 10 Class Auxiliary Data: COM 9

I opened PuTTY and selected Serial communication, COM 10 / COM 9 and input 9600 in the baud rate.

It opened the PuTTY console but there was nothing inside. I could not even type anything.

What I am doing wrong ?

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  • \$\begingroup\$ Make sure software and hardware flow control are disabled in the terminal program. \$\endgroup\$ – David Schwartz Sep 3 '16 at 7:03
  • \$\begingroup\$ Com9,10... Sounds like a USB to rs232 converter \$\endgroup\$ – JonRB Sep 3 '16 at 7:18
  • \$\begingroup\$ @JonRB this is the debugger \$\endgroup\$ – chris Sep 3 '16 at 7:35
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    \$\begingroup\$ It's "PuTTY" where the TTY is a reference to the old TeleTYpe. \$\endgroup\$ – Transistor Sep 3 '16 at 7:42
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    \$\begingroup\$ PuTTY diagnosis: just short pin 2 to 3 on your DB9 serial output and check whatever you type is echoed back. \$\endgroup\$ – carloc Sep 3 '16 at 8:19
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Ok, I am doing the same thing, with the same board and Putty. What you need to do is:

  1. Plug in the USB cable into the PC and connect to the Launchpad.
  2. Check in Windows Control Panel, there will be two ports listed - XDS110 Class Application/User UART (COM##) and XDS110 Class Auxilliary Data Port (COM##).
  3. Open Putty and use the COM port number for the XDS110 Class Application/User UART.
  4. Set the BAUD to 9600. 5) You should now be able to type in a character in PUTTY and have it echoed back.

I actually switched from Putty to RealTerm as I found it much better to use.

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  • \$\begingroup\$ Referring to comments above (I can't reply due to lack of points). The Launchpad uses the FTDI chip and associated drivers for all USB/Serial Comms. You may need to update your drivers from the FTDI website. I'm on Windows 10 (Anniversary Edition) and it works fine. Make sure you have the jumpers connected next to the TXD and RXD on the Launchpad otherwise you need to feed UART comms via DIO2 and DIO3 external pins. Hope this helps. \$\endgroup\$ – Mike Sep 30 '16 at 12:31

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