HAL_SPI_Transmit() API

[RS009]

I observed the data on both MOSI and MISO on logic analyzer, even when I use only one of the HAL_SPI_Transmit() or HAL_SPI_Receive(), why?

[gbm]

Cause this is how SPI works. The transfer always goes in both directions, even if one of the wires is not present. ;)

To receive, master must send data - it may be all zeros, all ones or some random stuff. The master may ignore received data but if there is some data signal from slave to master, the slave is sending something.

[RS009]

oh ok, got it, I think MISO line/wire comes to picture only when we use SPI_Receive API,

I want to write and read back one slave register how to do that?

e.g., Reg = 0x2C 10 1E, first byte is address and second two bytes are data,

 uint8_t Rx_Data[2];

  uint8_t R44[3] = {0x2C,0x10,0x1E};

 uint8_t Buf[]="Application is Running\n";

 HAL_UART_Transmit(&huart3, Buf, strlen((char *)Buf), 1000);

 HAL_GPIO_WritePin(GPIOF, GPIO_PIN_12, GPIO_PIN_SET);

 while (1)

 {

 while(! HAL_GPIO_ReadPin(GPIOC, GPIO_PIN_13));//on board user btn

 HAL_Delay(200);

 HAL_GPIO_WritePin(GPIOF, GPIO_PIN_12, GPIO_PIN_RESET);

 HAL_SPI_Transmit(&hspi1, R44, 1, 1000);

 HAL_SPI_Transmit(&hspi1, &R44[1], 2, 1000);

 HAL_GPIO_WritePin(GPIOF, GPIO_PIN_12, GPIO_PIN_SET);

 strcpy((char *)Buf,"Programming is Done\n");

 HAL_UART_Transmit(&huart3, Buf, strlen((char *)Buf), 1000);

 HAL_GPIO_WritePin(GPIOF, GPIO_PIN_12, GPIO_PIN_RESET);

 HAL_SPI_Transmit(&hspi1, R44, 1, 1000);

 HAL_SPI_Receive(&hspi1, Rx_Data, 2, 1000);

 HAL_GPIO_WritePin(GPIOF, GPIO_PIN_12, GPIO_PIN_SET);

 sprintf((char*)Buf,"Data is : 0x%X 0x%X \n",Rx_Data[0],Rx_Data[1]);

 HAL_UART_Transmit(&huart3,Buf, strlen((char *)Buf), 1000);

here is my code, please correct me if I am wrong, @Bold line, in logic analyzer I observed that it transmits 3 bytes, why?

[Wijeden RHIMI]

Hello @RS009 

Thank you for posting your issue !

• Could you please provide us a screenshot on which we can see the data In logic analyzer?

Best regards,

Wijeden,

[S.Ma]

I think chatGPT can explain SPI and how to generate code example snippets on STM32

[Pavel A.]

> I think chatGPT can explain SPI 

LOL. Could you share some example? We've already seen some bot generated posts here even so often.

[S.Ma]

Once chatGPT answers with formatted code source can be html linked, why not?