//******************************************************************************
//   MSP430F21x2 Demo - USCI_A0, UART 9600 Full-Duplex Transceiver, 32kHz ACLK
//
//   Description: USCI_A0 communicates continously as fast as possible full-
//   duplex with another device. Normal mode is LPM3, with activity only during
//   RX and TX ISR's. The TX ISR indicates the USCI_A0 is ready to send another
//   character. The RX ISR indicates the USCI_A0 has received a character. At
//   9600 baud, a full character is tranceived ~1ms.
//   The levels on P1.4/5 are TX'ed. RX'ed value is displayed on P1.0/1.
//   ACLK = BRCLK = LFXT1 = 32768Hz, MCLK = SMCLK = DCO ~1.2MHz
//   Baud rate divider with 32768Hz XTAL @9600 = 32768Hz/9600 = 3.41
//   //* An external watch crystal is required on XIN XOUT for ACLK *//
//
//                 MSP430F21x2                  MSP430F21x2
//              -----------------            -----------------
//             |              XIN|-      /|\|              XIN|-
//             |                 | 32kHz  | |                 | 32kHz
//             |             XOUT|-       --|RST          XOUT|-
//             |                 | /|\      |                 |
//             |              RST|---       |                 |
//             |                 |          |                 |
//           ->|P1.4             |          |             P1.0|-> LED
//           ->|P1.5             |          |             P1.1|-> LED
//       LED <-|P1.0             |          |             P1.4|<-
//       LED <-|P1.1             |          |             P1.5|<-
//             |     UCA0TXD/P3.4|--------->|P3.5             |
//             |                 |   9600   |                 |
//             |     UCA0RXD/P3.5|<---------|P3.4             |
//
//
//   A. Dannenberg
//   Texas Instruments Inc.
//   April 2006
//   Built with CCE Version: 3.2.0 and IAR Embedded Workbench Version: 3.41A
//******************************************************************************
#include "msp430x21x2.h"

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer
  P1OUT = 0x00;                             // P1.0/1 setup for LED output
  P1DIR = 0x03;
  P3SEL = 0x30;                             // P3.4,5 = USCI_A0 TXD/RXD
  UCA0CTL1 |= UCSSEL_1;                     // CLK = ACLK
  UCA0BR0 = 0x03;                           // 32kHz/9600 = 3.41
  UCA0BR1 = 0x00;
  UCA0MCTL = UCBRS1 + UCBRS0;               // Modulation UCBRSx = 3
  UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
  IE2 |= UCA0RXIE + UCA0TXIE;               // Enable USCI_A0 TX/RX interrupt

  __bis_SR_register(LPM3_bits + GIE);       // Enter LPM3 w/ interrupts enabled
}

// USCI A0/B0 Transmit ISR
#pragma vector=USCIAB0TX_VECTOR
__interrupt void USCI0TX_ISR(void)
{
  UCA0TXBUF = (P1IN >> 4) & 0x03;           // Read, justify, and transmit
}

// USCI A0/B0 Receive ISR
#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCI0RX_ISR(void)
{
  P1OUT = UCA0RXBUF;                        // Display RX'ed charater
}