msp430g2553串口通信_軟件串口

msp430g2553通過定時器A和軟件代碼配合可以形成串口，即軟件串口。當然msp430g2553也有硬件串口，內部有自己完整的uart模塊。
內部的uart參考：msp430g2533USCI_A0功能模塊硬件串口

一、代碼與仿真

在官方例程的基礎上，編寫了串口通信程序，並硬件測試通過 😉。

硬件測試用板（TI的MSP-EXP430G2ET）

串口測試助手的收發情況
打開板子，電腦端收到
MADE BY PengChengIT.
G2xx2 TimerA UART
READY.
通過電腦端向芯片發字符，發啥收啥。測試成功！

代碼說明：
接收：
1、接收啥發啥,通過for循環，持續進行
for(;; )
{
__bis_SR_register(LPM0_bits);
TimerA_UART_tx(rxBuffer);
}
}
2、接收的值存放在rxBuffer緩衝區內。
發送：
1、代碼中有發送函數，可以根據需要發送特定的字符；
①TimerA_UART_tx(unsigned char byte)，直接向函數輸入要發送的字節
②TimerA_UART_print(char *string)，可以直接向函數輸入要發送的一串文字、數字。
TimerA_UART_print(“MADE BY PengChengIT.\r\n”);
也可以發送字符串
char a_a[]=“pengchengIT”;
TimerA_UART_print(a_a);
引腳
1、P1.1TXD ， P1.2RXD
中斷
1、用2箇中斷函數，分別在接收和發送時觸發。

#include <msp430.h>

//------------------------------------------------------------------------------
// Hardware-related definitions
//------------------------------------------------------------------------------
#define UART_TXD   0x02                   // TXD on P1.1 (Timer0_A.OUT0)
#define UART_RXD   0x04                     // RXD on P1.2 (Timer0_A.CCI1A)

//------------------------------------------------------------------------------
// Conditions for 9600 Baud SW UART, SMCLK = 1MHz
//------------------------------------------------------------------------------
#define UART_TBIT_DIV_2     (1000000 / (9600 * 2))
#define UART_TBIT           (1000000 / 9600)

//------------------------------------------------------------------------------
// Global variables used for full-duplex UART communication
//------------------------------------------------------------------------------
unsigned int txData;                        // UART internal variable for TX
unsigned char rxBuffer;                     // Received UART character

//------------------------------------------------------------------------------
// Function prototypes
//------------------------------------------------------------------------------
void TimerA_UART_init(void);
void TimerA_UART_tx(unsigned char byte);
void TimerA_UART_print(char *string);

//------------------------------------------------------------------------------
// main()
//------------------------------------------------------------------------------
int main(void)
{
    WDTCTL = WDTPW + WDTHOLD;               // Stop watchdog timer
    if (CALBC1_1MHZ==0xFF)					// If calibration constant erased
    {											
      while(1);                               // do not load, trap CPU!!	
    }
    
    DCOCTL = 0;                             // Select lowest DCOx and MODx settings
    BCSCTL1 = CALBC1_1MHZ;                  // Set DCOCLK to 1MHz
    DCOCTL = CALDCO_1MHZ;
    P1SEL = UART_TXD + UART_RXD;            // Timer function for TXD/RXD pins
    P1DIR = 0xFF & ~UART_RXD;               // Set all pins but RXD to output

    __enable_interrupt();
    
    TimerA_UART_init();                     // Start Timer_A UART
   TimerA_UART_print("MADE BY PengChengIT.\r\n"); 
   TimerA_UART_print("G2xx2 TimerA UART\r\n");
    TimerA_UART_print("READY.\r\n");
    
    for (;;)
    {
        // Wait for incoming character
        __bis_SR_register(LPM0_bits);
        TimerA_UART_tx(rxBuffer);
    }
}
//------------------------------------------------------------------------------
// Function configures Timer_A for full-duplex UART operation
//------------------------------------------------------------------------------
void TimerA_UART_init(void)
{
    TACCTL0 = OUT;                          // Set TXD Idle as Mark = '1'
    TACCTL1 = SCS + CM1 + CAP + CCIE;       // Sync, Neg Edge, Capture, Int
    TACTL = TASSEL_2 + MC_2;                // SMCLK, start in continuous mode
}
//------------------------------------------------------------------------------
// Outputs one byte using the Timer_A UART
//------------------------------------------------------------------------------
void TimerA_UART_tx(unsigned char byte)
{
    while (TACCTL0 & CCIE);                 // Ensure last char got TX'd
    TACCR0 = TAR;                           // Current state of TA counter
    TACCR0 += UART_TBIT;                    // One bit time till first bit
    TACCTL0 = OUTMOD0 + CCIE;               // Set TXD on EQU0, Int
    txData = byte;                          // Load global variable
    txData |= 0x100;                        // Add mark stop bit to TXData
    txData <<= 1;                           // Add space start bit
}

//------------------------------------------------------------------------------
// Prints a string over using the Timer_A UART
//------------------------------------------------------------------------------
void TimerA_UART_print(char *string)
{
    while (*string) {
        TimerA_UART_tx(*string++);
    }
}
//------------------------------------------------------------------------------
// Timer_A UART - Transmit Interrupt Handler
//------------------------------------------------------------------------------
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = TIMER0_A0_VECTOR
__interrupt void Timer_A0_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(TIMER0_A0_VECTOR))) Timer_A0_ISR (void)
#else
#error Compiler not supported!
#endif
{
    static unsigned char txBitCnt = 10;

    TACCR0 += UART_TBIT;                    // Add Offset to CCRx
    if (txBitCnt == 0) {                    // All bits TXed?
        TACCTL0 &= ~CCIE;                   // All bits TXed, disable interrupt
        txBitCnt = 10;                      // Re-load bit counter
    }
    else {
        if (txData & 0x01) {
          TACCTL0 &= ~OUTMOD2;              // TX Mark '1'
        }
        else {
          TACCTL0 |= OUTMOD2;               // TX Space '0'
        }
        txData >>= 1;
        txBitCnt--;
    }
}      
//------------------------------------------------------------------------------
// Timer_A UART - Receive Interrupt Handler
//------------------------------------------------------------------------------
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = TIMER0_A1_VECTOR
__interrupt void Timer_A1_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(TIMER0_A1_VECTOR))) Timer_A1_ISR (void)
#else
#error Compiler not supported!
#endif
{
    static unsigned char rxBitCnt = 8;
    static unsigned char rxData = 0;

    switch (__even_in_range(TA0IV, TA0IV_TAIFG)) { // Use calculated branching
        case TA0IV_TACCR1:                        // TACCR1 CCIFG - UART RX
            TACCR1 += UART_TBIT;                 // Add Offset to CCRx
            if (TACCTL1 & CAP) {                 // Capture mode = start bit edge
                TACCTL1 &= ~CAP;                 // Switch capture to compare mode
                TACCR1 += UART_TBIT_DIV_2;       // Point CCRx to middle of D0
            }
            else {
                rxData >>= 1;
                if (TACCTL1 & SCCI) {            // Get bit waiting in receive latch
                    rxData |= 0x80;
                }
                rxBitCnt--;
                if (rxBitCnt == 0) {             // All bits RXed?
                    rxBuffer = rxData;           // Store in global variable
                    rxBitCnt = 8;                // Re-load bit counter
                    TACCTL1 |= CAP;              // Switch compare to capture mode
                    __bic_SR_register_on_exit(LPM0_bits);  // Clear LPM0 bits from 0(SR)
                }
            }
            break;
    }
}

二、代碼寄存器分析分析
配置軟件串口，涉及了時鐘的配置，IO的配置，定時器A的配置以及中斷函數，發送接收函數的編寫。
初始化
初始化的過程用到了多個寄存器，具體如下

寄存器名稱	涉及執行模式及說明
DCOCTL	時鐘寄存器
BCSCTL1	時鐘寄存器
TACCTL0	Timer_A寄存器、捕獲比較控制寄存器
TACCTL1	Timer_A寄存器、捕獲比較控制寄存器
TACTL	Timer_A寄存器、控制寄存器
PXSEL	IO口寄存器、功能選擇寄存器
PXDIR	IO口寄存器、設定輸入輸出方向

中斷函數
用到兩個中斷向量
TIMER0_A1_VECTOR
TIMER0_A0_VECTOR
發送函數
發送函數[ TimerA_UART_tx(unsigned char byte) ]用到的寄存器和參數整理如下

寄存器名稱/參數	執行模式及說明
TACCTL0	Timer_A寄存器、捕獲比較控制寄存器
TACCR0	Timer_A寄存器、捕獲比較寄存器
UART_TBIT/參數	波特率