I am using stm32f411 MCU to receive data over UART.
The MCU acts as a bridge between two devices. PC & Meter device. both uses UART, but the physical connection is different.
the connection between the MCU & meter is current mode communication.
Speed is 9600 bps.
I tested it with 2400 & 4800 & both were fine.
When I tested it with 9600, the signal on the receive pin of the stm32 is ok. There are some garbage character in between two messages, but it works fine on 2400 & 4800 baud-rate.
The code is very simple, receive data from meter & forward it to pc & vice versa. It does that when a complete message is received.
I added a delay to start receiving only after the sending and there is a small character appears when the MCU & the meter switch the ownership of the current mode bus. The meter reply come after 5ms of switching occurs.
I attached snapshot of what is received on the RX pin
The debug data
& snippet from the code for the UART.
void MX_USART2_UART_Init(void)
{
/* USER CODE BEGIN USART2_Init 0 */
/* USER CODE END USART2_Init 0 */
/* USER CODE BEGIN USART2_Init 1 */
/* USER CODE END USART2_Init 1 */
huart2.Instance = USART2;
huart2.Init.BaudRate = 9600;
huart2.Init.WordLength = UART_WORDLENGTH_8B;
huart2.Init.StopBits = UART_STOPBITS_1;
huart2.Init.Parity = UART_PARITY_EVEN;
huart2.Init.Mode = UART_MODE_TX_RX;
huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
huart2.Init.OverSampling = UART_OVERSAMPLING_16;
if (HAL_UART_Init(&huart2) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN USART2_Init 2 */
/* USER CODE END USART2_Init 2 */
}
///// on the bottom
else if (uartHandle->Instance == USART2)
{
/* USER CODE BEGIN USART2_MspInit 0 */
/* USER CODE END USART2_MspInit 0 */
/* USART2 clock enable */
__HAL_RCC_USART2_CLK_ENABLE();
__HAL_RCC_GPIOA_CLK_ENABLE();
/**USART2 GPIO Configuration
PA2 ------> USART2_TX
PA3 ------> USART2_RX
*/
GPIO_InitStruct.Pin = USART2_TX_Pin | USART2_RX_Pin;
GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
GPIO_InitStruct.Pull = GPIO_PULLUP;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
GPIO_InitStruct.Alternate = GPIO_AF7_USART2;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
/* USART2 interrupt Init */
HAL_NVIC_SetPriority(USART2_IRQn, 10, 0);
HAL_NVIC_EnableIRQ(USART2_IRQn);
/* USER CODE BEGIN USART2_MspInit 1 */
/* USER CODE END USART2_MspInit 1 */
}HAL_UARTEx_ReceiveToIdle(&huart6, &received_from_pc, sizeof(received_from_pc), &received_from_pc_len, 10000);
if (received_from_pc_len > 0)
{
/*--------------------------------------------------------------------------------*/
// HAL_Delay(500);
HAL_GPIO_WritePin(TX_ENABLE_GPIO_Port, TX_ENABLE_Pin, GPIO_PIN_RESET);
HAL_Delay(25);
HAL_UART_Transmit(&huart2, received_from_pc, received_from_pc_len, 3000); // for now.
HAL_Delay(10);
HAL_GPIO_WritePin(TX_ENABLE_GPIO_Port, TX_ENABLE_Pin, GPIO_PIN_SET);
/*--------------------------------------------------------------------------------*/
// discard garbage invalid characters until we receive a valid start of frame character (0x15, 0x06 or 0x02) due to communication problems
uint16_t total_rec = 0;
do
{
HAL_UARTEx_ReceiveToIdle(&huart2, &received_from_meter, sizeof(received_from_meter), &received_from_meter_len, 20);
total_rec += received_from_meter_len;
} while (received_from_meter_len > 0 && (received_from_meter[0] != 0x15 && received_from_meter[0] != 0x06 && received_from_meter[0] != 0x02 && received_from_meter[0] != '/'));
if (total_rec > 0)
{
HAL_UART_Transmit(&huart6, &received_from_meter, total_rec - 1, 3000);
}
}
}
Receive Data buffer
0xf
0x73
0x7e
0x5b
0x7b
0x6e
0xc
0xc