WHY MISO ECHO BACK WHAT MOSI SENT, EVEN THE MISO PIN IS ALREADY DISABLED.

[WM_IR]

I make a code that is just send SPI data, and the MISO should not return anything. Here is my code:

int main(void)

{

char user_data[] = "Hello World!";

GPIO_ButtonInit();

SPI2_GPIOInits();

SPI2_Inits();

SPI_SSOEConfig(SPI2,ENABLE);

  while(1)

  {

while(GPIO_ReadFromInputPin(GPIOC,GPIO_PIN_NO_13));

delay();

SPI_PeripheralControl(SPI2,ENABLE);

uint8_t dataLen = strlen(user_data);

SPI_SendData(SPI2,&dataLen,1);

SPI_SendData(SPI2,(uint8_t*)user_data,strlen(user_data));

while(SPI_GetFlagStatus(SPI2,SPI_BUSY_FLAG));

SPI_PeripheralControl(SPI2,DISABLE);

  }

return 0;

}

So, there should be no any SPI receivedata from MISO, but when I look the data at the logic analyzer, the MISO sent back the data from MOSI. It is like echoing, Or Is it because of the SPI nature?

this code I sent "Hello world!" the string length is 12.

First, I send the length of the string to the slave, Then, I send the Hello world! sentence to the slave.

the thing is, every data transmit from the MOSI, there will be a data sent back from MISO which is the sentence of the Hello world!

example in my picture, when I send the length 12, the MISO will exchange the " ! ". which is the last letter of hello world!

Then, when letter H is being sent, the MISO will reply back the length of the string data which is sent previously. Why is this happening? anyone can help me?

[WM_IR]

So, does the copied data from MISO is stored into my master Data register? If yes, do I need to clear it with dummy read in master?

[WM_IR]

I try to send the length of the string only to the master, for the first transmission, the MISO return 0xFF, I where does this value come? is it from the register that has not yet been cleared from MISO?

because after I do second transmission, the MISO return 0x0C which is the string length that I sent before.

 

To confirm it more, I change the code to send "hello world!" only string to the slave. and what I found is, the first thing that MISO return is the 0x0C data which is the data that I send previously before I change the code. Is this normal for the SPI?