//******************************************************************************
//  MSP-FET430P140 Demo - USART0 UART 2400 Ultra-low Power Echo ISR, 32kHz ACLK
//
//  Description; Echo a received character, RX ISR used. In the Mainloop UART0
//  is made ready to receive one character with interrupt active. The Mainloop
//  waits in LPM3. The UART0 ISR forces the Mainloop to exit LPM3 after 
//  receiving one character which echo's back the received character.
//  ACLK = UCLK0 = LFXT1 = 32768, MCLK = SMCLK = DCO ~ 800k  
//  Baud rate divider with 32768hz XTAL @2400 = 32768Hz/2400 = 13.65 (000Dh)
//  //*An external watch crystal is required on XIN XOUT for ACLK*//	  
//             
//                MSP430F149
//            -----------------
//        /|\|              XIN|-  
//         | |                 | 32kHz  
//         --|RST          XOUT|-
//           |                 |
//           |             P3.4|-----------> 
//           |                 | 2400 - 8N1
//           |             P3.5|<-----------
//
//       
//  M. Buccini
//  Texas Instruments, Inc
//  February 2002
//  Built with IAR Embedded Workbench Version: 1.25A
//******************************************************************************

#include <msp430x14x.h>

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;             // Stop WDT
  UCTL0 = CHAR;                         // 8-bit character
  UTCTL0 = SSEL0;                       // UCLK = ACLK
  UBR00 = 0x0D;                         // 32k/2400 - 13.65
  UBR10 = 0x00;                         //
  UMCTL0 = 0x6B;                        // Modulation
  ME1 |= UTXE0 + URXE0;                 // Enable USART0 TXD/RXD
  IE1 |= URXIE0;                        // Enable USART0 RX interrupt
  P3SEL |= 0x30;                        // P3.4,5 = USART0 TXD/RXD
  P3DIR |= 0x10;                        // P3.4 output direction
  _EINT();                              // Enable interrupts
  
// Mainloop
  for (;;)                             
  {
  _BIS_SR(LPM3_bits);                   // Wait in LPM3 until character RXed
  while ((IFG1 & UTXIFG0) == 0);        // USART0 TX buffer ready?
  TXBUF0 = RXBUF0;                      // RXBUF0 to TXBUF0
  }
}

// UART0 RX ISR will for exit from LPM3 in Mainloop
interrupt[UART0RX_VECTOR] void usart0_rx (void)
{
  _BIC_SR_IRQ(LPM3_bits);               // Clear LPM3 bits from 0(SR)
}