I want to use STM32F407VET6 board to send commands to Roboteq Motor Controller MDC2230 and I'm very newbie in embedded systems.

Firstly, I created my project via STM32CubeMX and connected RX and TX to each other. The loop-back worked correctly.

Also I can create communication between my PC and controller via RS232 to USB Converter. If I send "get Left Motor Speed" command via CuteCom, (It's: "?$03 1") Motor controller responds to PC without distortion successfully.

And also STM32 communicates with PC via that converter cable, sends and receives data correctly: I can see outputs of STM32 on CuteCom and can send commands to STM32.

At last, I connected controller to micro-controller. Here is the connection:

+--------------+        +-------------------+      +-------------------+
| "STM32"   TX |------->| R1OUT        R1IN |<-----| DATA OUT (Pin 2)  |
| "USART2"  RX |<-------| T1IN        T1OUT |----->| DATA IN (Pin 3)   |
|          GND |--------| GND           GND |------| GND               |
|         3.3V |--------| 3V-5.5V "MAX3232" |      | "Roboteq MDC2230" |
+--------------+        +-------------------+      +-------------------+

But in the case of STM32 to Roboteq Controller; STM32 sends first two bytes of buffer, wrong. It must be:

( 3f 24 30 33 20 31 0d ) "?$03 1\r" , but CuteCom(*) shows:

( bf 27 30 33 20 31 0d ) "¿'03 1\r" and sometimes(**):

( bf 27 38 33 20 31 0d ) "¿'83 1\r"

Here is some parts of code which works in other cases but not in above connection:


uint8_t tx_buff[MAX_COMMAND_STR_SIZE]; 
uint8_t rx_buff[MAX_COMMAND_STR_SIZE];
memset(tx_buff, 0x00, MAX_COMMAND_STR_SIZE * sizeof(uint8_t));
memset(rx_buff, 0x5F, MAX_COMMAND_STR_SIZE * sizeof(uint8_t));


sprintf((char*)tx_buff, "?$03 1\r");
while ( 1 )
        HAL_DMA_Init(&hdma_usart2_tx); // FIXME: Is needed?
        HAL_DMA_Init(&hdma_usart2_rx); // FIXME: Is needed?
        HAL_UART_Transmit_DMA ( &huart2, tx_buff, strlen((char*)tx_buff) );
        HAL_Delay ( 10 );
        HAL_UART_Receive_DMA ( &huart2, rx_buff, MAX_COMMAND_STR_SIZE );

        if ( DEBUG ) printf("tx_buff: %s\n", tx_buff);
        if ( DEBUG ) printf("rx_buff: %s\n", rx_buff);
        if ( DEBUG ) printf ( "DR: %"PRIu32"\n", huart2.Instance->DR );
        if ( DEBUG ) printf ( "ERR: %"PRIu32"\n\n", huart2.ErrorCode );
        //printf("Returned --> %d \n\n", getSpeedL(FALSE));


void dummyInit(UART_HandleTypeDef *_huart) // FIXME: if any other way exists, replace with this

    CLEAR_BIT(_huart->Instance->CR2, (USART_CR2_LINEN | USART_CR2_CLKEN));
    CLEAR_BIT(_huart->Instance->CR3, (USART_CR3_SCEN | USART_CR3_HDSEL | USART_CR3_IREN));


    /* Enable the peripheral */

    /* Initialize the UART state */
    _huart->ErrorCode = HAL_UART_ERROR_NONE;
    _huart->gState = HAL_UART_STATE_READY;
    _huart->RxState = HAL_UART_STATE_READY;
    _huart->RxXferCount = 0;
    _huart->TxXferCount = 0;

(*) I'm using some lazy way to read communication between max3232's T1OUT and Roboteq's DATA IN pin. My RS232 to USB converter connected to my pc, and there is M-F Jumper cable on RS232 side. I'm just touching to T1OUT of MAX232.

(**) And CuteCom shows output with noise.

What are the wrong parts of my approach? I know, my first fault is being a Software Engineer, not an Electrical Engineer.


It seems like you have some sort of 7/8 bit format mix-up in your STM32. The difference between the expected and unexpected data is that the MS bit is set. For example, 0x03 vs 0x83 in: ( bf 27 30 33 20 31 0d ) "¿'83 1\r"

Your message format seems to only require 7-bit ASCII values. Study the UART specifications for the STM32 to see if there is some distinction between 7 bit and 8 bit data operation or setup. Also, try ANDing all byte values with 0x7F just prior to loading them into the UART's xmit data register.

  • \$\begingroup\$ Thanks for an answer. I tried changing UART_WORDLENGTH_8B to UART_WORDLENGTH_9B but not worked, The problem was occured because of wrong connection. \$\endgroup\$ – Orhan G. Hafif Jul 14 '16 at 13:06

I writed true connections between MAX3232 and Roboteq MDC2230(!) but writed wrong connections between STM32 and MAX3232 in Question. So, connected wrong pins between MAX3232 and Roboteq only! On real case, T1OUT was connected to DATA OUT(Pin2). True connection is:

+--------------+        +-------------------+      +-------------------+
| "STM32"   RX |<-------| R1OUT        R1IN |<-----| DATA OUT (Pin 2)  |
| "USART2"  TX |------->| T1IN        T1OUT |----->| DATA IN (Pin 3)   |
|          GND |--------| GND           GND |------| GND               |
|         3.3V |--------| 3V-5.5V "MAX3232" |      | "Roboteq MDC2230" |
+--------------+        +-------------------+      +-------------------+

Asking question had been good for me. But for the community, I think it was unnecessary. Sorry Dear Community, my bad :P


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