MSP430G2XX2 调试USI问题

void SPI_init(void)
{
P1DIR |= 0X60; //P1.5,P1.6 OUTPUT
// P1DIR &= ~BIT7; //P1.7 INPUT
P1SEL |= BIT6+BIT5; //P1.5 SCLK;P1.6 SDO;

USICTL0 |= USIPE6+USIPE5+USIMST+USIOE; //SDO,SCLK,Master,data output
USICTL1 |= USIIE; //Enable interrupt
USICKCTL |= USIDIV_2+USISSEL_1; //ACLK,4分频
USICTL0 &= ~USISWRST; // USI released for operation
USICNT |= USI16B+USICNT4; //16 bit data
USISR = 0Xffff;
_EINT();
}

谢谢