MSP430F5438A 串口问题

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//******************************************************************************
//! This example shows how to configure the UART module as the loopback to
//! verify that received data is sent data.
//!
//!               MSP430F5438A
//!             -----------------
//!       RST -|     P3.4/UCA0TXD|----|
//!            |                 |    |
//!            |                 |    |
//!            |     P3.5/UCA0RXD|----|
//!            |                 |
//!
//!
//! This example uses the following peripherals and I/O signals.  You must
//! review these and change as needed for your own board:
//! - UART peripheral
//! - GPIO Port peripheral (for UART pins)
//! - UCA0TXD
//! - UCA0RXD
//!
//! This example uses the following interrupt handlers.  To use this example
//! in your own application you must add these interrupt handlers to your
//! vector table.
//! - USCI_A0_VECTOR.
//******************************************************************************
#include "driverlib.h"

//*****************************************************************************
//
//Select Baud rate
//
//*****************************************************************************
#define BAUD_RATE                               9600
//*****************************************************************************
//
//Initialize received data
//
//*****************************************************************************
uint8_t receivedData = 0x00;
//*****************************************************************************
//
//Initialize trasnmit data
//
//*****************************************************************************
uint8_t transmitData = 0x00;

uint8_t check = 0;

void main(void)
{
    //Stop WDT
    WDT_A_hold(WDT_A_BASE);
    
    //P3.4,5 = USCI_A0 TXD/RXD
    GPIO_setAsPeripheralModuleFunctionInputPin(
        GPIO_PORT_P9,
        GPIO_PIN4 + GPIO_PIN5
        );

    //Baudrate = 9600, clock freq = 1.048MHz
    //UCBRx = 109, UCBRFx = 0, UCBRSx = 2, UCOS16 = 0
    USCI_A_UART_initParam param = {0};
    param.selectClockSource = USCI_A_UART_CLOCKSOURCE_SMCLK;
    param.clockPrescalar = 109;
    param.firstModReg = 0;
    param.secondModReg = 2;
    param.parity = USCI_A_UART_NO_PARITY;
    param.msborLsbFirst = USCI_A_UART_LSB_FIRST;
    param.numberofStopBits = USCI_A_UART_ONE_STOP_BIT;
    param.uartMode = USCI_A_UART_MODE;
    param.overSampling = USCI_A_UART_LOW_FREQUENCY_BAUDRATE_GENERATION;

    if(STATUS_FAIL == USCI_A_UART_init(USCI_A2_BASE, &param))
    {
        return;
    }

    //Enable UART module for operation
    USCI_A_UART_enable(USCI_A2_BASE);

    //Enable Receive Interrupt
    USCI_A_UART_clearInterrupt(USCI_A2_BASE,
                               USCI_A_UART_RECEIVE_INTERRUPT);
    USCI_A_UART_enableInterrupt(USCI_A2_BASE,
                                USCI_A_UART_RECEIVE_INTERRUPT);

    __enable_interrupt();

    while(1)
    {
        transmitData = transmitData + 1;                      // Increment TX data
        // Load data onto buffer
        USCI_A_UART_transmitData(USCI_A2_BASE,
                                 transmitData);
        while(check != 1)
        {
            ;
        }
        check = 0;
    }
}

//******************************************************************************
//
//This is the USCI_A0 interrupt vector service routine.
//
//******************************************************************************
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=USCI_A2_VECTOR
__interrupt
#elif defined(__GNUC__)
__attribute__((interrupt(USCI_A2_VECTOR)))
#endif
void USCI_A2_ISR(void)
{
  
    switch(__even_in_range(UCA2IV,4))
    {
    //Vector 2 - RXIFG
    case 2:
        receivedData = USCI_A_UART_receiveData(USCI_A2_BASE);

//        if(!(receivedData == transmitData))                       // Check value
//        {
//            while(1)
//            {
//                ;
//            }
//        }
        check = 1;
        break;
    default: break;
    }
}