C Program Pulse Width Modulation

C Program Pulse Width Modulation

How to write a C Program Pulse Width Modulation in C Programming Language ?


 This C Program Pulse Width Modulation.

Description: This code controls a servo using PWM via Timer A.  Three external buttons are used to change the servo's position.  Button 0 rotates the servo CCW in 5ms increments.  Button 1 rotates the servo to its center position.  Button 2 rotates the servo CW in 5ms increments.

Solution:

  1. #include <msp430.h>
  3. /*
  4.  * main.c
  5.  *Pulse Width Modulation
  6.  *
  7.  * Description:
  8.  * This code controls a servo using PWM via Timer A.  Three external buttons are used to change
  9.  * the servo's position.  Button 0 rotates the servo CCW in 5ms increments.  Button 1 rotates
  10.  * the servo to its center position.  Button 2 rotates the servo CW in 5ms increments.
  11.  *
  12.  */
  14. #define ms_20        655   // 20.0 ms
  16. int PositionIndex = 6;
  18. int main(void)
  19. {
  20.   WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
  21.   P1DIR |= BIT2;                            // P1.2 output
  23.   P2IE |= BIT0 + BIT1 + BIT2;               // Interrupt enabled for external buttons
  24.   P2IES &= ~(BIT0 + BIT1 + BIT2);           // Interrupt low to high enable
  25.   P2IFG &= ~(BIT0 + BIT1 + BIT2);           // IFG clear
  27.   // Using P1.2 for hardware set/reset as when TAR hits CCRO and CCR1 values.
  28.   // This allows P1.2 to toggle outside of software control.  Note that Timer A
  29.   // is running compare mode but interrupts are not being utilized.
  30.   // Note that this feature of toggling port bits outside of software control
  31.   // may be utilized while cpu is in low power mode.
  32.   P1SEL |= BIT2;                            // P1.2 TA1/2 options
  34.   // Setting CCR0 for a 20 ms period with CCTL1 determining pulse width (duty
  35.   // cycle) as determined by OUTMOD_7.
  36.   CCR0 = ms_20 - 1;                         // PWM Period of 20 ms
  37.   CCTL1 = OUTMOD_7;                         // CCR1 reset/set
  38.   TACTL = TASSEL_1 + MC_1;                  // ACLK, up mode
  40.   _enable_interrupt();
  42.   while(1);
  44. }
  46. #pragma vector=PORT2_VECTOR
  47. __interrupt void Port_2(void)
  48. {
  50.     // if statement determines when rotated to the max position (CW or CCW)
  51.     if(PositionIndex > 11){
  52.         PositionIndex = 11;
  53.     }
  54.     else if(PositionIndex < 1){
  55.         PositionIndex = 1;
  56.     }
  57.     else{
  58.     }
  60.     // if statement controls the servo based on button press
  61.     if((P2IFG & BIT0) == BIT0){
  62.            PositionIndex--;
  63.            P2IFG &= ~BIT0;
  64.         }
  65.     else if((P2IFG & BIT2) == BIT2){
  66.         PositionIndex++;
  67.         P2IFG &= ~BIT2;
  68.     }
  69.     else{
  70.         PositionIndex = 6;
  71.         P2IFG &= ~BIT1;
  72.     }
  74.     CCR1 = (PositionIndex*5) + 20; // update servo's position based on PositionIndex value
  76. }


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