MSP430FR5969 Launchpad UART example

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 *                       MSP430 CODE EXAMPLE DISCLAIMER
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 * MSP430 code examples are self-contained low-level programs that typically
 * demonstrate a single peripheral function or device feature in a highly
 * concise manner. For this the code may rely on the device's power-on default
 * register values and settings such as the clock configuration and care must
 * be taken when combining code from several examples to avoid potential side
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 * for an API functional library-approach to peripheral configuration.
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//******************************************************************************
//  MSP430FR59xx Demo - eUSCI_A0 UART echo at 9600 baud using BRCLK = 8MHz
//
//  Description: This demo echoes back characters received via a PC serial port.
//  SMCLK/ DCO is used as a clock source and the device is put in LPM3
//  The auto-clock enable feature is used by the eUSCI and SMCLK is turned off
//  when the UART is idle and turned on when a receive edge is detected.
//  Note that level shifter hardware is needed to shift between RS232 and MSP
//  voltage levels.
//
//  The example code shows proper initialization of registers
//  and interrupts to receive and transmit data.
//  To test code in LPM3, disconnect the debugger.
//
//  ACLK = VLO, MCLK =  DCO = SMCLK = 8MHz
//
//                MSP430FR5969
//             -----------------
//       RST -|     P2.0/UCA0TXD|----> PC (echo)
//            |                 |
//            |                 |
//            |     P2.1/UCA0RXD|<---- PC
//            |                 |
//
//   P. Thanigai
//   Texas Instruments Inc.
//   August 2012
//   Built with IAR Embedded Workbench V5.40 & Code Composer Studio V5.5
//******************************************************************************
#include "msp430.h"

int main(void)
{
  WDTCTL = WDTPW | WDTHOLD;                 // Stop Watchdog

  // Configure GPIO
  P2SEL1 |= BIT0 | BIT1;                    // USCI_A0 UART operation
  P2SEL0 &= ~(BIT0 | BIT1);

  // Disable the GPIO power-on default high-impedance mode to activate
  // previously configured port settings
  PM5CTL0 &= ~LOCKLPM5;

  // Startup clock system with max DCO setting ~8MHz
  CSCTL0_H = CSKEY >> 8;                    // Unlock clock registers
  CSCTL1 = DCOFSEL_3 | DCORSEL;             // Set DCO to 8MHz
  CSCTL2 = SELA__VLOCLK | SELS__DCOCLK | SELM__DCOCLK;
  CSCTL3 = DIVA__1 | DIVS__1 | DIVM__1;     // Set all dividers
  CSCTL0_H = 0;                             // Lock CS registers

  // Configure USCI_A0 for UART mode
  UCA0CTLW0 = UCSWRST;                      // Put eUSCI in reset
  UCA0CTLW0 |= UCSSEL__SMCLK;               // CLK = SMCLK
  // Baud Rate calculation
  // 8000000/(16*9600) = 52.083
  // Fractional portion = 0.083
  // User's Guide Table 21-4: UCBRSx = 0x04
  // UCBRFx = int ( (52.083-52)*16) = 1
  UCA0BR0 = 52;                             // 8000000/16/9600
  UCA0BR1 = 0x00;
  UCA0MCTLW |= UCOS16 | UCBRF_1;
  UCA0CTLW0 &= ~UCSWRST;                    // Initialize eUSCI
  UCA0IE |= UCRXIE;                         // Enable USCI_A0 RX interrupt

  __bis_SR_register(LPM3_bits | GIE);       // Enter LPM3, interrupts enabled
  __no_operation();                         // For debugger
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=USCI_A0_VECTOR
__interrupt void USCI_A0_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCI_A0_VECTOR))) USCI_A0_ISR (void)
#else
#error Compiler not supported!
#endif
{
  switch(__even_in_range(UCA0IV, USCI_UART_UCTXCPTIFG))
  {
    case USCI_NONE: break;
    case USCI_UART_UCRXIFG:
      while(!(UCA0IFG&UCTXIFG));
      UCA0TXBUF = UCA0RXBUF;
      __no_operation();
      break;
    case USCI_UART_UCTXIFG: break;
    case USCI_UART_UCSTTIFG: break;
    case USCI_UART_UCTXCPTIFG: break;
  }
}