MSP430 SPI slave

spi_slave.c

#include "msp430g2553.h"
#include <legacymsp430.h>

int main(void)
{
    WDTCTL = WDTPW + WDTHOLD;                 	// Stop watchdog timer
    WDTCTL  = WDTPW + WDTHOLD; 			// Stop WDT
    BCSCTL1 = CALBC1_1MHZ;      		// Set DCO
    DCOCTL  = CALDCO_1MHZ;

    P1DIR  = BIT0 + BIT6; 		// P1.0 and P1.6 are the red+green LEDs
    P1OUT  = BIT0 + BIT6; 		// All LEDs off

    P1SEL = BIT1 + BIT2 + BIT4;
    P1SEL2 = BIT1 + BIT2 + BIT4;

    UCA0CTL1 = UCSWRST;                       // **Put state machine in reset**
    UCA0CTL0 |= UCCKPL + UCMSB + UCSYNC;      // 3-pin, 8-bit SPI slave 
    UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
    IE2 |= UCA0RXIE;                          // Enable USCI0 RX interrupt

    __bis_SR_register(GIE);       // Enter LPM4, enable interrupts

    volatile unsigned int i = 0;

    while(1) {

        P1OUT ^= BIT6; 			// Toggle P1.6 output (green LED) using exclusive-OR
        i = 50000;             		// Delay

        do (i--);	
        while (i != 0);
    }

	return 0;
}

// Echo character
interrupt(USCIAB0RX_VECTOR) USCI0RX_ISR(void)
{
    while (!(IFG2 & UCA0TXIFG));            	// USCI_A0 TX buffer ready?
    UCA0TXBUF = UCA0RXBUF;
    P1OUT ^= BIT0; 				// Toggle P1.0 output (red LED) using exclusive-OR
}