//******************************************************************************
//  MSP430x11x1 Demo - Timer_A, Ultra-Low Pwr UART 9600 Echo, No XTAL, ROSC
//
//  Description: This program demonstrates a half-duplex 9600-baud UART using
//  Timer_A3 using no XTAL and an external resistor for DCO ROSC. DCO used for
//  TACLK UART baud generation. The program will wait in LPM4, echoing back
//  a received character using 8N1 protocol. On valid RX character, the
//  character is echoed back.
//  Using a 100k resistor on ROSC, with default DCO setting, set DCOCLK ~ 2MHz.
//  ACLK = n/a, MCLK = SMCLK ~2MHz DCOCLK
//  //* Use of external resistor reduces temperature sensitivity of DCOCLK *//
//
//               MSP430F1121
//            -----------------
//  /|\   /|\|              XIN|-
//   |     | |                 |
//  100k   --|RST          XOUT|-
//   |       |                 |
//   +-------|P2.5/ROSC        |
//           |   CCI0A/TXD/P1.1|-------->
//           |                 | 9600 8N1
//           |   CCI0B/RXD/P2.2|<--------
//
#define RXD   0x04                          // RXD on P2.2
#define TXD   0x02                          // TXD on P1.1

//   Conditions for 9600 Baud SW UART, DCO ~ 2MHz

#define Bitime_5  104                       // ~ 0.5 bit length
#define Bitime    208                       // ~ 9615 baud

unsigned int RXTXData;
unsigned char BitCnt;

void TX_Byte (void);
void RX_Ready (void);

//  M. Buccini / Z. Albus
//  Texas Instruments Inc.
//  May 2005
//  Built with Code Composer Essentials Version: 1.0
//*****************************************************************************

#include <msp430x11x1.h>

void main (void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer
  BCSCTL2 |= DCOR;                          // Rosc
  _BIS_SR(OSCOFF);                          // XTAL not used
  CCTL0 = OUT;                              // TXD Idle as Mark
  TACTL = TASSEL_2 + MC_2;                  // SMCLK, continuous mode
  P1SEL = TXD;                              // P1.1/TA0 for TXD function
  P1DIR = TXD;                              // TXD output on P1
  P2SEL = RXD;                              // P2.2/TA0 as RXD input

// Mainloop
  for (;;)
  {
  RX_Ready();                               // UART ready to RX one Byte
  _BIS_SR(LPM4_bits + GIE);                 // Enter LPM0 w/ interr until char RXed
  TX_Byte();                                // TX Back RXed Byte Received
  }
}

// Function Transmits Character from RXTXData Buffer
void TX_Byte (void)
{
  BitCnt = 0xA;                             // Load Bit counter, 8data + ST/SP
  CCR0 = TAR;                               // Current state of TA counter
  CCR0 += Bitime;                           // Some time till first bit
  RXTXData |= 0x100;                        // Add mark stop bit to RXTXData
  RXTXData = RXTXData << 1;                 // Add space start bit
  CCTL0 = OUTMOD0 + CCIE;                   // TXD = mark = idle
  while ( CCTL0 & CCIE );                   // Wait for TX completion
}

// Function Readies UART to Receive Character into RXTXData Buffer
// Sync capture not possible as DCO=TACLK=SMCLK can be off !!
void RX_Ready (void)
{
  BitCnt = 0x8;                             // Load Bit counter
  CCTL0 = CM1 + CCIS0 + OUTMOD0 + CAP + CCIE;  // Neg Edge, Cap
}

// Timer A0 interrupt service routine
__interrupt void Timer_A0 (void);
TIMERA0_ISR(Timer_A0)
__interrupt void Timer_A0 (void)
{
  CCR0 += Bitime;                           // Add Offset to CCR0

// RX
  if (CCTL0 & CCIS0)                        // RX on CCI0B?
  {
    if( CCTL0 & CAP )                       // Capture mode = start bit edge
    {
    CCTL0 &= ~ CAP;                         // Switch from capture to compare mode
    CCR0 += Bitime_5;
    _BIC_SR_IRQ(SCG1 + SCG0);               // DCO reamins on after reti
    }
    else
    {
    RXTXData = RXTXData >> 1;
      if (CCTL0 & SCCI)                     // Get bit waiting in receive latch
      RXTXData |= 0x80;
      BitCnt --;                            // All bits RXed?
      if ( BitCnt == 0)
//>>>>>>>>>> Decode of Received Byte Here <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
      {
      CCTL0 &= ~ CCIE;                      // All bits RXed, disable interrupt
      _BIC_SR_IRQ(CPUOFF);                  // Active mode on reti 0(SR)
      }
//>>>>>>>>>> Decode of Received Byte Here <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    }
  }
// TX
  else
  {
    if ( BitCnt == 0)
    CCTL0 &= ~ CCIE;                        // All bits TXed, disable interrupt
    else
    {
      CCTL0 |=  OUTMOD2;                    // TX Space
      if (RXTXData & 0x01)
      CCTL0 &= ~ OUTMOD2;                   // TX Mark
      RXTXData = RXTXData >> 1;
      BitCnt --;
    }
  }
}