请教一个关于LPC1788的SSP程序的问题，收发函数不理解
void SSPSend( uint32_t portnum, uint8_t *buf, uint32_t Length ){
uint32_t i;
uint8_t Dummy = Dummy;
for ( i = 0; i < Length; i++ )
{
/* Move on only if NOT busy and TX FIFO not full. */
while ( (LPC_SSP0->SR & (SSPSR_TNF|SSPSR_BSY)) != SSPSR_TNF );
LPC_SSP0->DR = *buf;
buf++;
while ( (LPC_SSP0->SR & (SSPSR_BSY|SSPSR_RNE)) != SSPSR_RNE ); //这个地方为什么要加上这一句呢？
/* Whenever a byte is written, MISO FIFO counter increments, Clear FIFO
on MISO. Otherwise, when SSP0Receive() is called, previous data byte
is left in the FIFO. */
Dummy = LPC_SSP0->DR;
}
}
void SSPReceive( uint32_t portnum, uint8_t *buf, uint32_t Length )
{
uint32_t i;
for ( i = 0; i < Length; i++ )
{
/* As long as Receive FIFO is not empty, I can always receive. */
/* If it's a loopback test, clock is shared for both TX and RX,
no need to write dummy byte to get clock to get the data */
/* if it's a peer-to-peer communication, SSPDR needs to be written
before a read can take place. */
LPC_SSP0->DR = 0xFF; //这里为什么要发送0xFFT呢？
/* Wait until the Busy bit is cleared */
while ( (LPC_SSP0->SR & (SSPSR_BSY|SSPSR_RNE)) != SSPSR_RNE );
*buf++ = LPC_SSP0->DR;
}
} while ( (LPC_SSP0->SR & (SSPSR_BSY|SSPSR_RNE)) != SSPSR_RNE );//因为SSP0是边发边收的，所以要检测BSY，RNE位，不然会冲掉现有的数据FIFO是只有8字节
LPC_SSP0->DR = 0xFF;//主机要接收先要发送数据才能启动时钟SCK0，只要发送数据就可以也可以是0X00
希望这些是你想要的答案。 cjh8894 发表于 2012-12-25 16:52 static/image/common/back.gif
while ( (LPC_SSP0->SR & (SSPSR_BSY|SSPSR_RNE)) != SSPSR_RNE );//因为SSP0是边发边收的，所以要检测BS ...
非常感谢{:3_48:}
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