MSP430F21x2: USCI SPI Clk Problem

//******************************************************************************

#include "msp430x21x2.h"

int commUCA(int);

unsigned char MST_Data, SLV_Data;

void main(void)

{

  volatile unsigned int i;

  WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer

  BCSCTL3 = LFXT1S_2;            // Select ACLK from VLO (no crystal)

  BCSCTL1 = CALBC1_8MHZ;          // Calibrated range for DCO

  DCOCTL = CALDCO_8MHZ;            // Calibrated tap and modulation

  P1OUT = 0x00;                             // reset outputs

  P1DIR = 0x00;                             // Inputs

  P2OUT = BIT5 | BIT7;            // set to 1 EN & EN2

  P2DIR = BIT5 | BIT7;            // Set dir out (EN & EN2)

  P3OUT = 0x00;                             // Set slave reset

  P3DIR |= 0x00;                            //

  P3SEL |= 0x31;                            // P3.0,4,5 USCI_A0 option select

  UCA0CTL0 |= UCCKPL + UCMSB + UCMST + UCSYNC;  // 3-pin, 8-bit SPI master

  UCA0CTL1 |= UCSSEL_2;                     // SMCLK

  UCA0BR0 |= 0x02;                          // /2(always write something!)

  UCA0BR1 = 0;                              //

  UCA0MCTL = 0;                             // No modulation

  UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**

  IE2 |= UCA0RXIE;                          // Enable USCI0 RX interrupt

  for (i = 50; i > 0; i--);                 // Wait for slave to initialize

  MST_Data = 0x55;                          // Initialize data values

  SLV_Data = 0x00;

  for(;;){

  commUCA(MST_Data);                     // Transmit first character

  }

}

int commUCA(int TX_Data){

  UCA0TXBUF = TX_Data;

  __low_power_mode_0();

  return UCA0RXBUF;

}

// ISR for Received interrupt

#pragma vector=USCIAB0RX_VECTOR

__interrupt void USCIA0RX_ISR(void)

{

  volatile unsigned int i;

  int dummy = 0;

  while (!(IFG2 & UCA0TXIFG));              // USCI_A0 TX buffer ready?

  dummy = UCA0RXBUF;

  for (i = 3000; i; i--);                     // Add time between transmissions

  dummy++;

  __low_power_mode_off_on_exit();

}