/*## Configure the SPI4 peripheral ###*/

Spi4Handle.Instance            	= SPI4;   //use STM32F429 SPI4
Spi4Handle.Init.Direction      	= SPI_DIRECTION_2LINES_RXONLY;
Spi4Handle.Init.CLKPhase       	= SPI_PHASE_1EDGE;    //read at DCLK falling edge
Spi4Handle.Init.CLKPolarity   	 = SPI_POLARITY_HIGH; //read at DCLK falling edge 
Spi4Handle.Init.DataSize      	= SPI_DATASIZE_8BIT;  //or 16BIT
Spi4Handle.Init.NSS            	= SPI_NSS_HARD_INPUT; //make /CS low active
Spi4Handle.Init.Mode 		= SPI_MODE_SLAVE;     //MCU SPI4 as SPI Slave

/*## Enable EXTI0 and SPI4 to Receive AD7768 Data bits ###*/
// clear EXTI0 IT flag prior to enable external interrupt 0 !!!

__HAL_GPIO_EXTI_CLEAR_IT(KEY_BUTTON_PIN);
HAL_NVIC_EnableIRQ(EXTI0_IRQn);

// wait for EXTI0 interrupt (/DRDY rising edge) to prepare for reading last conversion data

if (EXTI0_Flag == SET)
{
	EXTI0_Flag = RESET;//clear /DRDY rising edge flag variable
	// throw out the last byte/word captured in the previous ODR cycle !!!
	Rx_temp = *(__IO uint8_t *)&Spi4Handle.Instance->DR;		__HAL_SPI_ENABLE(&Spi4Handle);
	// SPI4_CNVByteNum is the total data byte number to read in one conversion cycle
	while (SPI4_ByteCount < SPI4_CNVByteNum)
 	{
		// Check the RXNE flag 
 		if (__HAL_SPI_GET_FLAG(&Spi4Handle, SPI_FLAG_RXNE))//
 		 {
			// transfer the received data from DR register to memory
			SPI_RxBuffer[RxBuf_Idn] = *(__IO uint8_t *)&Spi4Handle.Instance->DR;
			RxBuf_Idn++;
  	     		SPI4_ByteCount++;
    	  	}
	}
// disable SPI4 to prevent read in extra data after all channel codes finished due to /DRDY is low active and DCLK continuously pulses
	__HAL_SPI_DISABLE(&Spi4Handle);	
	SPI4_CNVCount++;
	RxBuf_Idn = SPI4_CNVCount * SPI4_CNVByteNum;					SPI4_ByteCount = 0;
}//end of if (EXTI0_Flag == SET)

else
{//*** other software jobs ***//}
/*## handles External 0 interrupt request ###*/
// EXTI0 rising edge triggered to leave more response time for going into EXTI0_IRQHandler !!!
void EXTI0_IRQHandler(void)
{
	  if(__HAL_GPIO_EXTI_GET_IT(EXTI0) != RESET)
  	{
// enable SPI4 as soon as possible, and make sure before the first DCLK falling edge after /DRDY falling !!!
		__HAL_SPI_ENABLE(&Spi4Handle);
		__HAL_GPIO_EXTI_CLEAR_IT(EXTI0);
		EXTI0_Flag = SET;
	}
}