//******************************************************************************
//  MSP-FET430P430 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 = 32xACLK = 1.048576Mhz  
//  Baud rate divider with 32768hz XTAL @2400 = 32768Hz/2400 = 13.65 (000Dh)
//  //*An external watch crystal is required on XIN XOUT for ACLK*//	  
//              
//                MSP430FG439
//             -----------------
//         /|\|              XIN|-  
//          | |                 | 32kHz  
//          --|RST          XOUT|-
//            |                 |
//            |             P2.4|-----------> 
//            |                 | 2400 - 8N1
//            |             P2.5|<-----------
//
//       
//  M.Buccini
//  Texas Instruments, Inc
//  June 2004
//  Built with IAR Embedded Workbench Version: 2.21B
//******************************************************************************

#include <msp430xG43x.h>

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;             // Stop WDT
  FLL_CTL0 |= XCAP18PF;                 // Configure load caps
  P2SEL |= 0x30;                        // P2.4,5 = USART0 TXD/RXD
  ME1 |= UTXE0 + URXE0;                 // Enable USART0 TXD/RXD
  UCTL0 |= CHAR;                        // 8-bit character
  UTCTL0 |= SSEL0;                      // UCLK = ACLK
  UBR00 = 0x0D;                         // 32k/2400 - 13.65
  UBR10 = 0x00;                        
  UMCTL0 = 0x6B;                        // Modulation
  UCTL0 &= ~SWRST;                      // Initialize USART state machine
  IE1 |= URXIE0;                        // Enable USART0 RX interrupt
  
// Mainloop
  for (;;)                             
  {
  _BIS_SR(LPM3_bits + GIE);             // Enter LPM3 w/interrupt
  while (!(IFG1 & UTXIFG0));            // USART0 TX buffer ready?
  TXBUF0 = RXBUF0;                      // RXBUF0 to TXBUF0
  }
}

// UART0 RX ISR will for exit from LPM3 in Mainloop
#pragma vector=UART0RX_VECTOR
__interrupt void usart0_rx (void)
{
  _BIC_SR_IRQ(LPM3_bits);               // Clear LPM3 bits from 0(SR)
}