（急）SPI总线问题

外接串口Flash，使用4线SPI总线，问题：模式设置为 UCMODE_2 时，执行完UCA1CTL1 &= ~UCSWRST;之后，UCFE就被置1，请问是什么原因？

程序如下：

P8SEL |= BIT1 + BIT2 + BIT3 + BIT4; 

UCA1CTL1 |= UCSWRST; // **Put state machine in reset**
UCA1CTL0 |= UCMST + UCSYNC + UCCKPL + UCMSB + UCMODE_2 ;//+ UCSTEM ; // 4-pin, 8-bit SPI master

// Clock polarity high, MSB

UCA1CTL1 |= UCSSEL_0 ;// SMCLK
UCA1BR0 = 0x02; // /2
UCA1BR1 = 0; //
UCA1MCTL = 0; // No modulation
UCA1CTL1 &= ~UCSWRST; // **Initialize USCI state machine**
UCA1IE |= UCRXIE;