//******************************************************************************
//   MSP430x24x Demo - USCI_A1, SPI 3-Wire Slave Data Echo
//
//   Description: SPI slave talks to SPI master using 3-wire mode. Data received
//   from master is echoed back.  USCI RX ISR is used to handle communication,
//   CPU normally in LPM4.  Prior to initial data exchange, master pulses
//   slaves RST for complete reset.
//   ACLK = n/a, MCLK = SMCLK = DCO ~1.045Mhz
//
//   Use with SPI Master Incremented Data code example.  If the slave is in
//   debug mode, the reset signal from the master will conflict with slave's
//   JTAG; to work around, use IAR's "Release JTAG on Go" on slave device.  If
//   breakpoints are set in slave RX ISR, master must stopped also to avoid
//   overrunning slave RXBUF.
//
//                MSP430F249
//             -----------------
//         /|\|              XIN|-
//          | |                 |
//          | |             XOUT|-
// Master---+-|RST              |
//            |             P3.7|<- Data Out (UCA1SOMI)
//            |                 |
//            |             P3.6|-> Data In (UCA1SIMO)
//            |                 |
//            |             P5.0|<- Serial Clock In (UCA1CLK)
//
//  B. Nisarga
//  Texas Instruments Inc.
//  September 2007
//  Built with IAR Embedded Workbench Version: 3.42A
//******************************************************************************
#include "msp430x24x.h" 

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer
  BCSCTL1 = CALBC1_1MHZ;                    // Set DCO to 1MHz
  DCOCTL = CALDCO_1MHZ;
 
  while (!(P5IN & 0x01));                   // If clock sig from mstr stays low,
                                            // it is not yet in SPI mode
  P3SEL |= 0x0C0;                           // P3.6,7 USCI_A1 option select
  P5SEL |= 0x01;                            // P5.0 USCI_A1 option select
  UCA1CTL1 = UCSWRST;                       // **Put state machine in reset**
  UCA1CTL0 |= UCCKPL + UCMSB + UCSYNC;      // 3-pin, 8-bit SPI master
  UCA1CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
  UC1IE |= UCA1RXIE;                          // Enable USCI1 RX interrupt

  __bis_SR_register(LPM4_bits + GIE);       // Enter LPM4, enable interrupts
}

// Echo character
#pragma vector=USCIAB1RX_VECTOR
__interrupt void USCI1RX_ISR (void)
{
  while (!(UC1IFG & UCA1TXIFG));              // USCI_A1 TX buffer ready?
  UCA1TXBUF = UCA1RXBUF;
}