Stm32f103 Ведомый режим передачи

Question

Я могу получить данные в режиме прерывания, но не могу отправить данные от ведомого к ведущему.

  SystemInit();
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOC |RCC_APB2Periph_SPI1| RCC_APB2Periph_AFIO , ENABLE);

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_6 ;            
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;  
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5|GPIO_Pin_7;           
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;  
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;          
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;  
  GPIO_Init(GPIOC, &GPIO_InitStructure);    


  SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
  SPI_InitStructure.SPI_Mode = SPI_Mode_Slave;
  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
  SPI_InitStructure.SPI_CPOL = SPI_CPOL_High;
  SPI_InitStructure.SPI_CPHA = SPI_CPHA_2Edge;
  SPI_InitStructure.SPI_NSS = SPI_NSS_Hard;
  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_64;
  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
  SPI_InitStructure.SPI_CRCPolynomial = 10;

  NVIC_PriorityGroupConfig(NVIC_PriorityGroup_0);
  NVIC_InitStructure.NVIC_IRQChannel = SPI1_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 5;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);

  SPI_Init(SPI1, &SPI_InitStructure);
  SPI_I2S_ITConfig(SPI1, SPI_I2S_IT_RXNE, ENABLE);
  SPI_I2S_ITConfig(SPI1, SPI_I2S_IT_TXE, ENABLE);
  SPI_Cmd(SPI1, ENABLE);    
  while(1)
  {
      SPI_I2S_SendData(SPI1, "QWERTY");
  }