SPI读,没有时钟信号输出的吗?

只看该作者 · 2014-10-28 15:54

我用MPS430G2333 的SPI接口连接外部芯片,发现在SPI读的时候没有时钟信号CLK输出的?.
P1.4:STE    P1.5:CLK    P1.6:SOMI    P1.7:SIMO
的设置如下:
  P1SEL |= BIT5+BIT6+BIT7;    // Set SPI peripheral bits
  P1SEL2 |= BIT5+BIT6+BIT7;
  P1DIR |= BIT4+BIT5+BIT7;    // STE, SCLK, and DOUT as output
  P1DIR &= ~BIT6;                   // Din as input
  P1OUT |=BIT4;                   // Set STE high
  UCB0CTL1 |= UCSWRST;       // Enable SW reset
  UCB0CTL0 |= UCMSB+UCCKPH+UCMST+UCSYNC; // [b0] 1 -  Synchronous mode
  // [b2-1] 00-  3-pin SPI
  // [b3] 1 -  Master mode
  // [b4] 0 - 8-bit data
  // [b5] 1 - MSB first
  // [b6] 0 - Clock polarity high.
  // [b7] 1 - Clock phase - Data is captured on the first UCLK edge and changed on the following edge.

  UCB0CTL1 |= UCSSEL_2;             // SMCLK
  UCB0BR0 = 0xFF;                            // 16 MHz
  UCB0BR1 = 0;                               //
  UCB0CTL1 &= ~UCSWRST;             // Clear SW reset, resume operation
  UC0IE |= UCB0RXIE;
  UC0IFG &= ~UCB0RXIFG;

我用SPI发数据是这样的:
  UCB0TXBUF = reg_address;
  while ( (UCB0STAT & UCBUSY) ); // USCI_B1 TX buffer ready?
这样CLK 和SMIO都有正确的脉冲输出哦!
但我读SPI,比如这样:
  S_buf = UCB0RXBUF;
就根本没有CLK的脉冲时钟输出啊?读不到数据.是我那里方法不对吗?

谢谢!