{"id":12977,"date":"2024-06-07T12:22:18","date_gmt":"2024-06-07T09:22:18","guid":{"rendered":"https:\/\/deepbluembedded.com\/?p=12977"},"modified":"2024-06-10T05:18:28","modified_gmt":"2024-06-10T02:18:28","slug":"stm32-uart-half-duplex-single-wire-tutorial-example","status":"publish","type":"post","link":"https:\/\/deepbluembedded.com\/stm32-uart-half-duplex-single-wire-tutorial-example\/","title":{"rendered":"STM32 UART Half-Duplex (Single Wire) Tutorial & Examples"},"content":{"rendered":"\n

In this tutorial, we’ll discuss how the STM32 UART Half-Duplex (Single Wire)<\/strong> mode works. You’ll learn how to use the STM32 UART half-duplex mode to send and receive data over UART with a single wire.<\/p>\n\n\n\n

We’ll implement an example project for STM32 UART Half-Duplex Transmitter\/Receiver<\/strong> to practice what we’ll learn in this tutorial by creating two-way communication between two STM32 board over UART in half-duplex mode. Without further ado, let’s get right into it!<\/p>\n\n\n

Table of Contents<\/h2>\n
    \n
  1. STM32 UART Half-Duplex (Single Wire) Mode<\/a>\n\n<\/li>\n
  2. How To Send Data With STM32 UART Half-Duplex<\/a>\n\n<\/li>\n
  3. How To Receive Data With STM32 UART Half-Duplex<\/a>\n\n<\/li>\n
  4. STM32 UART Half-Duplex Example Overview<\/a>\n\n<\/li>\n
  5. STM32 UART Half-Duplex (Single Wire) Example<\/a>\n\n\n<\/li>\n\n<\/li>\n\n
  6. Wrap Up<\/a>\n<\/li><\/ol>\n\n\n
    \n\n\n

    STM32 UART Half-Duplex (Single Wire) Mode<\/strong><\/h2>\n\n\n

    The STM32 UART can be configured to operate in half-duplex mode (single wire). In this mode, the UART module can send or receive data using only one wire (line) but not at the same time. It keeps switching between transmitter mode and receiver mode in runtime to achieve this behavior.<\/p>\n\n\n\n

    In single-wire half-duplex mode, the TX and RX pins are connected internally. The RX pin is no longer used. The TX pin is always released when no data is transmitted. Thus, it acts as a standard IO in idle or in reception. This means that the IO must be configured so that TX pin is in alternate-function open-drain mode with an external pull-up resistor. <\/p>\n\n\n\n

    The STM32 UART hardware may or may not have this pull-up internally. This should be mentioned in the datasheet of the exact STM32 microcontroller. For the demo example I’ve created and tested on my hardware, it was necessary to hook up an external pull-up resistor to get it working reliably. A 4.7k\u03a9<\/strong> resistor to Vcc<\/strong> should be fine for most situations.<\/p>\n\n\n\n

    \n\n\n

    How To Send Data With STM32 UART Half-Duplex<\/strong><\/h2>\n\n\n

    To send data in half-duplex mode with STM32 UART, you need first to enable TX using the HAL_HalfDuplex_EnableTransmitter()<\/code> function. Then, you can send the data you want to send over UART in half-duplex mode, and switch back to the RX (receiver) mode to capture any incoming data.<\/p>\n\n\n\n

    Here is an example code for how this is done using STM32 HAL APIs:<\/p>\n\n\n

    \/\/ Enable TX (Half-Duplex Mode)\nHAL_HalfDuplex_EnableTransmitter(&huart1);\n\n\/\/ Send The Data You Want!\nHAL_UART_Transmit(&huart1, UART1_TxBuffer, UART_TX_BUFFER_SIZE, 100);\n\n\/\/ Switch Back To RX (Receiver Mode)\nHAL_HalfDuplex_EnableReceiver(&huart1);<\/pre>\n\n\n
    <\/p>\n\n\n\n
    \n\n\n
    How To Receive Data With STM32 UART Half-Duplex<\/strong><\/h2>\n\n\n
    To receive data in half-duplex mode with STM32 UART, you need first to enable RX using the HAL_HalfDuplex_EnableReceiver()<\/code> function. Then, you can receive data over UART in half-duplex mode. It’s better to use the IDLE Line Detection<\/a><\/strong> Receiving scheme to read any unknown number of incoming data bytes and make sure to have the UART interrupt enabled in the NVIC settings.<\/p>\n\n\n\n
    Here is an example code for how this is done using STM32 HAL APIs:<\/p>\n\n\n
    int main(void)\n{\n  ...\n  HAL_HalfDuplex_EnableReceiver(&huart1);\n  HAL_UARTEx_ReceiveToIdle_IT(&huart1, UART1_RxBuffer, UART_RX_BUFFER_SIZE);\n  ...\n}\n\nvoid HAL_UARTEx_RxEventCallback(UART_HandleTypeDef *huart, uint16_t Size)\n{\n  RxDataLen = Size;\n  \/\/ Process The Received Data & Update PWM Outputs\n  ...\n  \/\/ Re-Start The Receive Operation Again\n  HAL_UARTEx_ReceiveToIdle_IT(&huart1, UART1_RxBuffer, UART_RX_BUFFER_SIZE);\n}<\/pre>\n\n\n
    <\/p>\n\n\n\n
    \n\n\n
    STM32 UART Half-Duplex Example Overview<\/strong><\/h2>\n\n\n
    In the following example project, we’ll design a two-way communication system between two STM32 microcontrollers using the UART half-duplex single-wire mode.<\/p>\n\n\n\n
    In this system, each STM32 microcontroller will do the following functions:<\/p>\n\n\n\n