SPI constantly sending Clock and OxFF over MOSI after enabling SPI in half duplex.

[milindmishra87]

Hi,

I have been trying to communicate with an SPI peripheral (NOR Flash). I want to use SPI in half duplex mode. The problem is that as soon as enable the SPI peripheral I see SPI constantly sending OxFF over MOSI even though I have not written anything on the SPI DR register.

Pasting the screenshot of the Salea LA

Below is the simple SPI TX code

void SPI_SendData(uint8_t* Txdata, uint32_t len) {

    if((spi_dev->SR & TXE_FLAG)) {

      spi_dev->DR = *(uint8_t*)Txdata;

      Txdata++;

      len--;

    }

  if(!(spi_dev->CR1 & SPI_EN)) {

    spi_dev->CR1 |= SPI_EN;

  }

  while(len > 0) {

    // Wait for TXE FLAG

    if((spi_dev->SR & TXE_FLAG)) {

      spi_dev->DR = *(uint8_t*)Txdata;

      Txdata++;

      len--;

    }

  }

}

[TDK]

In half duplex mode, you need to toggle between sending and receiving. When receiving, it is clocked constantly as shown in your logic analyzer traces.