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//******************************************************************************
//  MSP430G2xx1 Demo - Timer_A, Ultra-Low Pwr UART 9600 Echo, 32kHz ACLK
//
//  Description: Use Timer_A CCR0 hardware output modes and SCCI data latch
//  to implement UART function @ 9600 baud. Software does not directly read and
//  write to RX and TX pins, instead proper use of output modes and SCCI data
//  latch are demonstrated. Use of these hardware features eliminates ISR
//  latency effects as hardware insures that output and input bit latching and
//  timing are perfectly synchronised with Timer_A regardless of other
//  software activity. In the Mainloop the UART function readies the UART to
//  receive one character and waits in LPM3 with all activity interrupt driven.
//  After a character has been received, the UART receive function forces exit
//  from LPM3 in the Mainloop which configures the port pins (P1 & P2) based
//  on the value of the received byte (i.e., if BIT0 is set, turn on P1.0).
 
//  ACLK = TACLK = LFXT1 = 32768Hz, MCLK = SMCLK = default DCO
//  //* An external watch crystal is required on XIN XOUT for ACLK *//  
//
  //******************************************************************************
 
#include "msp430g2231.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()
//------------------------------------------------------------------------------
void main(void)
{
    WDTCTL = WDTPW + WDTHOLD;               // Stop watchdog timer
 
    DCOCTL = 0x00;                          // Set DCOCLK to 1MHz
    BCSCTL1 = CALBC1_1MHZ;
    DCOCTL = CALDCO_1MHZ;
 
    P1OUT = 0x00;                           // Initialize all GPIO
    P1SEL = UART_TXD + UART_RXD;            // Timer function for TXD/RXD pins
    P1DIR = 0xFF & ~UART_RXD;               // Set all pins but RXD to output
    P2OUT = 0x00;
    P2SEL = 0x00;
    P2DIR = 0xFF;
 
    __enable_interrupt();
 
    TimerA_UART_init();                     // Start Timer_A UART
    TimerA_UART_print("G2xx1 TimerA UART\r\n");
    TimerA_UART_print("READY.\r\n");
 
    for (;;)
    {
        // Wait for incoming character
        __bis_SR_register(LPM0_bits);
 
        // Update board outputs according to received byte
        if (rxBuffer & 0x01) P1OUT |= 0x01; else P1OUT &= ~0x01;    // P1.0
        if (rxBuffer & 0x02) P1OUT |= 0x08; else P1OUT &= ~0x08;    // P1.3
        if (rxBuffer & 0x04) P1OUT |= 0x10; else P1OUT &= ~0x10;    // P1.4
        if (rxBuffer & 0x08) P1OUT |= 0x20; else P1OUT &= ~0x20;    // P1.5
        if (rxBuffer & 0x10) P1OUT |= 0x40; else P1OUT &= ~0x40;    // P1.6
        if (rxBuffer & 0x20) P1OUT |= 0x80; else P1OUT &= ~0x80;    // P1.7
        if (rxBuffer & 0x40) P2OUT |= 0x40; else P2OUT &= ~0x40;    // P2.6
        if (rxBuffer & 0x80) P2OUT |= 0x80; else P2OUT &= ~0x80;    // P2.7
 
        // Echo received character
        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
//------------------------------------------------------------------------------
#pragma vector = TIMERA0_VECTOR
__interrupt void Timer_A0_ISR(void)
{
    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
//------------------------------------------------------------------------------
#pragma vector = TIMERA1_VECTOR
__interrupt void Timer_A1_ISR(void)
{
    static unsigned char rxBitCnt = 8;
    static unsigned char rxData = 0;
 
    switch (__even_in_range(TAIV, TAIV_TAIFG)) { // Use calculated branching
        case TAIV_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;
    }
}
//------------------------------------------------------------------------------