Posted on August 04, 2011 at 19:29Thank you clive1. My problem was I was not clearing the RXNE flag after sending out the first byte. When I send my first byte out on the SPI line, the RX buffer is being filled with a 'garbage byte' from the external IC. Therefore, the RXNE flag is set. So, I need to read this byte out of the rx buff to clear the flag, then send my garbage byte. Here is my code for anybody trying to write a simple SPI byte read fcn without using interrupts.
uint8_t MicsRead(uint8_t Addr)
{
uint8_t RxData;
// put a '1' in front of value to change format of address to a read
Addr |= 0x80;
// disable ints
// bring chip select low
_MICS_CS_LOW;
// send Addr over SPI
SPI_I2S_SendData(SPI1,Addr);
// wait until TXE = 1
while(SPI_I2S_GetFlagStatus(SPI1,SPI_I2S_FLAG_TXE) != SET);
// wait until RXNE = 1
while(SPI_I2S_GetFlagStatus(SPI1,SPI_I2S_FLAG_RXNE) != SET);
// read the rx buff to clear the RXNE flag (garbage)
RxData = (uint8_t)(SPI_I2S_ReceiveData(SPI1));
// send garbage byte over SPI
SPI_I2S_SendData(SPI1,0x00);
// wait until TXE = 1
while(SPI_I2S_GetFlagStatus(SPI1,SPI_I2S_FLAG_TXE) != SET);
// wait for RXNE = 1
while(SPI_I2S_GetFlagStatus(SPI1,SPI_I2S_FLAG_RXNE) != SET);
// read in rx byte
RxData = (uint8_t)(SPI_I2S_ReceiveData(SPI1));
// wait until TXE = 1
while(SPI_I2S_GetFlagStatus(SPI1,SPI_I2S_FLAG_TXE) != SET);
// wait until BSY = 0
while(SPI_I2S_GetFlagStatus(SPI1,SPI_I2S_FLAG_BSY) != RESET);
// bring chip select high
_MICS_CS_HI;
// enable ints
return(RxData);
}
