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IHPY

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  1. I'm new to MSP430 and I'm trying to do a frequency/period measurement. I've read about timers and get the main concepts though I'm still learning. To get an idea of how they work, I'm using this code. It outputs a PWM on one pin which I connect to another pin for capturing period: http://coecsl.ece.illinois.edu/ge423/datasheets/MSP430Ref_Guides/Cexamples/MSP430G2xx3 Code Examples/C/msp430g2xx3_ta_21.c 

    After making some modifications (removing unneeded code to light led and adding calculations for frequency) it works with the original pins. However, I want to change which input pin will take measurements. I want pin 2.0 to do so. Currently, TimerA0 captures and TimerA1 outputs PWM. Since PIN 2.0 uses TimerA1 and not A0,  I assumed I would just need to flip the timers and pins. However, it's not working. I looked at the datasheet and can't figure out whats wrong. What am I missing? Here is my code:

     

     

    #include <msp430.h>
    
    unsigned char Count, First_Time;
    unsigned int REdge1, REdge2, FEdge;
    
    int main(void)
    {
      unsigned int Period, ON_Period;
      unsigned char DutyCycle;
    
      WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer
    
    //  P1SEL |= BIT0;
      if (CALBC1_8MHZ==0xFF)					// If calibration constant erased
      {											
        while(1);                               // do not load, trap CPU!!	
      }
      DCOCTL = 0;                               // Select lowest DCOx and MODx settings
      BCSCTL1 = CALBC1_8MHZ;                    // Set DCO to 8MHz
      DCOCTL = CALDCO_8MHZ;
    
      // Configure Port Pins
      P1DIR |= BIT2;                            // P2.1/TA1.1 Output
      P1SEL |= BIT2;                            // TA1.1 Option select
      P2DIR &= ~BIT0;                           // P1.1/TA0.1 Input Capture
      P2SEL |= BIT0;                            // TA0.1 option select
    
      // Configure TA1.1 to output PWM signal
      // Period = 82/32khz = 2.5ms ~ 400Hz Freq
      TA0CCR0 = 82-1;                          // Period Register
      TA0CCR1 = 21;                            // TA1.1 25% dutycycle
      TA0CCTL1 |= OUTMOD_7;                    // TA1CCR1, Reset/Set
      TA0CTL = TASSEL_1 + MC_1 + TACLR;        // ACLK, upmode, clear TAR
    
      // Configure the TA0CCR1 to do input capture
      TA1CCTL1 = CAP + CM_3 + CCIE + SCS + CCIS_0;
                                                // TA0CCR1 Capture mode; CCI1A; Both
                                                // Rising and Falling Edge; interrupt enable
      TA1CTL |= TASSEL_2 + MC_2 + TACLR;        // SMCLK, Cont Mode; start timer
    
      // Variable Initialization
      Count = 0x0;
      First_Time = 0x01;
    
      while(1)
      {
          __bis_SR_register(LPM0_bits + GIE);   // Enter LPM0
          __no_operation();                     // For debugger
          // On exiting LPM0
          if (TA1CCTL1 & COV)                   // Check for Capture Overflow
              while(1);                         // Loop Forever
    
          Period = REdge2 - REdge1;             // Calculate Period
          ON_Period = FEdge-REdge1;             // On period
          DutyCycle = ((unsigned long)ON_Period*100/Period);
    
      }
    }
    
    // TA0_A1 Interrupt vector
    #pragma vector = TIMER1_A1_VECTOR
    __interrupt void TIMER1_A1_ISR (void)
    {
      switch(__even_in_range(TA1IV,0x0A))
      {
          case  TA1IV_NONE: break;              // Vector  0:  No interrupt
          case  TA1IV_TACCR1:                   // Vector  2:  TACCR1 CCIFG
            if (TA1CCTL1 & CCI)                 // Capture Input Pin Status
            {
                // Rising Edge was captured
                if (!Count)
                {
                    REdge1 = TA1CCR1;
                    Count++;
                }
                else
                {
                    REdge2 = TA1CCR1;
                    Count=0x0;
                    __bic_SR_register_on_exit(LPM0_bits + GIE);  // Exit LPM0 on return to main
                }
    
                if (First_Time)
                    First_Time = 0x0;
            }
            else
            {
                // Falling Edge was captured
                if(!First_Time)
                {
                    FEdge = TA1CCR1;
                }
            }
            break;
          case TA1IV_TACCR2: break;             // Vector  4:  TACCR2 CCIFG
          case TA1IV_6: break;                  // Vector  6:  Reserved CCIFG
          case TA1IV_8: break;                  // Vector  8:  Reserved CCIFG
          case TA1IV_TAIFG: break;              // Vector 10:  TAIFG
          default: 	break;
      }
    }

    I checked and there is a pulse going into P2.0 but P2.0 is not capturing it. Is it just not possible with this pin or am I missing something obvious?

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