#include  "msp430x44x.h"
//******************************************************************************
//  MSP430-TEST44X Demo - Comp_A Slope ADC to Detect Temp Level Set P5.1 > 25c  
//
//  Description: Comparator_A is used to detect a resistance threashold.  
//  Discharge times of a 0.1uf capacitor through a 10k-NTC (25c) and 10k ohm 
//  reference resistor are compared.  If the NTC discharge time is is lower
//  than the 10k referece, P5.1 is set.  If the NTC discharge time is higher
//  than refernce, P5.1 is reset.  The LED is ON if the temperature is greater
//  than 25c. 
//  ACLK = n/a, MCLK = SMCLK = default DCO ~ 800k 
//
//               MSP430F449
//            -----------------
//       /|\ |              XIN|-  
//        |  |                 |
//        ---|RST          XOUT|-
//           |                 | 
//     +-10k-|P1.0             |
//     |     |                 |	
//     +-NTC-|P1.7             |
//     |     |                 |
//     +-----|P1.6         P5.1|-->LED
//     |     |                 |
//    ===.1uf|                 |
//     |     |                 |			
//     ------|VSS
//
//           NTC = 10k @25c, (P/N 271-110A Radio Shack)
//
unsigned int sensor_time;
unsigned int ref_time;
unsigned int timer_count;
unsigned int measure(int);  // measures the time to discharge the capacitor

#define Ref     (0x01)      // P1.0 = Reference
#define Sensor  (0x80)      // P1.7 = Sensor
//
//  Yang Rui
//  Lierda, Inc
//  MAY 2004
//  Built with IAR Embedded Workbench Version: 1.26B
//******************************************************************************

void main (void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
  P5OUT &= ~0x02;                           // P5.1 reset
  P5DIR |= 0x02;                            // P5.1 output direction
  P1OUT &= ~(Ref + Sensor);                 // Ref set
  P1DIR |= Ref + Sensor;                    // Ref output
  CACTL1 = CARSEL + CAREF0 + CAON;          // -Comp = 0.25*Vcc - on
  CACTL2 = P2CA0;                           // +Comp = 1.6
  TACTL = TASSEL_2 + MC_2;                  // SMCLK, clear TAR
  _EINT();                                  // Enable interrupts
  
  while (1)                                 // Mainloop
  {
     sensor_time = measure(Sensor);         // Measure discharge time through sensor
     ref_time = measure(Ref);               // Measure discharge time through Ref
     if (sensor_time < ref_time)            // if sensor time < ref time ( >25c )
      P5OUT |= 0x02;                        // LED on - Set P5.1
     else P5OUT &= ~0x02;                   // LED off - Reset P5.1
  }
}

unsigned int measure(int source) {            
  P1OUT |= Ref;                             // Ref Set
  P1DIR |= Ref;                             // Ref output
  CCR1 = TAR + 5000;                        // CCR1 ~ TAR+5ms
  CCTL1 = CCIE;                             // Comp,interrupt
  LPM0;                                     // Wait for CCR1 interrupt
  P1DIR &= ~Ref;                            // Ref = HiZ, Charge complete
  P1OUT &= ~Ref;                            // Ref = Reset
  CCTL1 = CM_2 + CCIS_1 + CAP + CCIE;       // Neg, CCIB,Cap,interrupt
  timer_count = TAR;                        // TAR at before discharge
  P1DIR |= source;                          // Temp = Sensor or Ref
  LPM0;                                     // Wait for CCR1 interrupt
  timer_count = CCR1 - timer_count;         // timer_count = discharge time
  P1DIR &= ~(Sensor + Ref);                 // Disable Sensor or Ref
  CCTL1 = 0x00;                             // Disable CCTL1
  return(timer_count);
} 

// Timer A1 interrupt service routine
interrupt[TIMERA1_VECTOR] void Timer_A(void)
{
 switch( TAIV )
 {
   case  2: LPM0_EXIT;                      // ccr1
            break;
 }
}