STM32F407F4 Discovery: USART Master-Slave Communication Issue

[Mohammed_sanaulla]

I’m trying to establish USART communication between two STM32F407-Discovery boards, where one board acts as Master and the other as Slave.

Hardware setup
Master Board clk -> save board Clk  - [common clock]
Master Board TX → Slave Board RX
Master Board RX ← Slave Board TX
Both GND connected
Using STM32F407-Discovery boards
  
SYNCHRONOUS MODE

connectivity configurations

• USART port used (e.g., USART2)

• Baud rate (e.g., 115200)

• Word length (8 bits)

• Parity (None)

• Stop bits (1)

• Clock settings ( synchronous) 
  clock polarity : low
  clock phase : one edge
  
  code of master and slave:

  // Master
  char data = 'A';
  HAL_USART_Transmit(&huart2, (uint8_t*)&data, 1, HAL_MAX_DELAY);

  // Slave
  char rx;
  HAL_USART_Receive(&huart2, (uint8_t*)&rx, 1, HAL_MAX_DELAY);
  
  

  output : Im getting grbage value like 127@ , so on
  
  What I've tried 
  - Verified TX/RX wiring
  - Checked baud rate matching
  - Tried loopback test on each board (TX→RX)
  - Switched from polling to interrupt-based reception
  
  

 

[SMSAD.1]

HAL USART Initialization

Hello Mohammed

You need to initialize the USART peripheral with synchronous mode enabled and clock configured properly.

Here is a snipped code that could help you

Example initialization snippet for Master:

huart2.Instance = USART2;
huart2.Init.BaudRate = 115200;
huart2.Init.WordLength = UART_WORDLENGTH_8B;
huart2.Init.StopBits = UART_STOPBITS_1;
huart2.Init.Parity = UART_PARITY_NONE;
huart2.Init.Mode = UART_MODE_TX_RX;
huart2.Init.CLKPolarity = UART_POLARITY_LOW;
huart2.Init.CLKPhase = UART_PHASE_1EDGE;
huart2.Init.LastBit = UART_LASTBIT_ENABLE; // Important for synchronous mode
HAL_USART_Init(&huart2);

For Slave, the configuration is similar but the clock is received:

huart2.Init.Mode = UART_MODE_TX_RX;
huart2.Init.CLKPolarity = UART_POLARITY_LOW;
huart2.Init.CLKPhase = UART_PHASE_1EDGE;
huart2.Init.LastBit = UART_LASTBIT_ENABLE;
HAL_USART_Init(&huart2);

[Mohammed_sanaulla]

Hello sir, Thank you for your guidance.
I tried initializing the USART in synchronous mode using the configuration you shared. The initialization works fine, but when I send a single byte from the master to the slave, I’m receiving unexpected data (for example, value 255  in the Live Expressions during debugging).
Could you please help me understand why I might be receiving this garbage data even though the clock and configuration seem correct?
i will be grateful if u help me out with this

 

[EXUE.2]

I have checked your code, there is no problem. 

How about loopback test on each board (TX→RX)? also is failed? did you have check the waveform of the TX/RX/Clock by oscilloscope?