I have a weight cell which replies to specific frames over RS485 (cell contains its own communication protocol). Manufacturer has a software to test the cell so I connect it to my pc using a RS485 to USB converter and I am able to connect to the cell and send/receive frames. Here are the parameters I use and you can see TX-RX frames below:
Now I want to manage this protocol with a STM32 board but I am not receiving frames properly. I am using NUCLEO-F401RE and RS485 CAN Shield from Waveshare (https://www.waveshare.com/wiki/RS485_CAN_Shield). Here is what I do and my UART configuration:
Main program
int main(void)
{
HAL_Init();
SystemClock_Config();
MX_GPIO_Init();
GPIO_InitStruct.Pin = GPIO_PIN_8;
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
GPIO_InitStruct.Pull = GPIO_NOPULL;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
MX_USART1_UART_Init();
MX_USART2_UART_Init();
printf("NUCLEOF401RE - RS485 RX\r\n");
while (1)
{
// Activate sending status
HAL_GPIO_WritePin (GPIOA, GPIO_PIN_8, 1);
txBuffer[0] = 0x44; // SOF
txBuffer[1] = 0x01; // DIR
txBuffer[2] = 0x00; // ERR
txBuffer[3] = 0x25; // CMD
txBuffer[4] = 0x00; // DATOS0
txBuffer[5] = 0x00; // DATOS1
txBuffer[6] = 0x00; // DATOS2
txBuffer[7] = 0x00; // DATOS3
txBuffer[8] = txBuffer[1] ^ txBuffer[2] ^ txBuffer[3] ^ txBuffer[4] ^ txBuffer[5] ^ txBuffer[6] ^ txBuffer[7]; // CRC
txBuffer[9] = 0x0A; // EOF
printf("TX - Sending frame\r\n");
HAL_UART_Transmit(&UART_RS485, txBuffer, framelength, 1000);
// Activate receiving status
HAL_GPIO_WritePin (GPIOA, GPIO_PIN_8, 0);
HAL_UART_Receive(&UART_RS485, rxBuffer, framelength, 1000);
printf("RX - Reception Completed:\r\n");
for(int j=0; j<framelength; j++)
{
printf("Byte %d: %02X\r\n", j, rxBuffer[j]);
}
HAL_Delay(3000);
}
UART Configuration
static void MX_USART1_UART_Init(void)
{
UART_RS485.Instance = USART1;
UART_RS485.Init.BaudRate = 115200;
UART_RS485.Init.WordLength = UART_WORDLENGTH_8B;
UART_RS485.Init.StopBits = UART_STOPBITS_1;
UART_RS485.Init.Parity = UART_PARITY_NONE;
UART_RS485.Init.Mode = UART_MODE_TX_RX;
UART_RS485.Init.HwFlowCtl = UART_HWCONTROL_NONE;
UART_RS485.Init.OverSampling = UART_OVERSAMPLING_16;
if (HAL_UART_Init(&UART_RS485) != HAL_OK)
{
Error_Handler();
}
}
void HAL_UART_MspInit(UART_HandleTypeDef* huart)
{
GPIO_InitTypeDef GPIO_InitStruct = {0};
if(huart->Instance==USART1)
{
__HAL_RCC_USART1_CLK_ENABLE();
__HAL_RCC_GPIOA_CLK_ENABLE();
GPIO_InitStruct.Pin = GPIO_PIN_9;
GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
GPIO_InitStruct.Pull = GPIO_NOPULL;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
GPIO_InitStruct.Alternate = GPIO_AF7_USART1;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
GPIO_InitStruct.Pin = GPIO_PIN_10;
GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
GPIO_InitStruct.Pull = GPIO_PULLUP;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
GPIO_InitStruct.Alternate = GPIO_AF7_USART1;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
}
I should be receiving a frame starting with 0x44 and ending with 0x0A based on the cell protocol. However, this is what I receive:
I have tried many different UART parameters, many different pin configurations and tried using a 120 ohm and 220 ohm resistors between A and B lines but nothing works. What am I missing?
