msp430: servo pwm test

servo_test.c

// a PWM signal is created with the TimerA0 where CCR0 is the periode 20ms and CCR1 the duty cycle
// the PWM signal is output through pin P1.6 that correspond to TA0.1 (see MSP430G2553 uC datasheet)
// this code does not generate interruptions but uses the reset/set mode to generate the PWM signal when the timer counts up to CCR1
// in this case a duty cycle of 2ms (CCR1 = 2000 - 1) will rotate the axis clockwise (see sg90 datasheet)
// a duty cycle of 1.0ms (CCR1 = 1000 - 1) will rotate the axis anticlockwise
// a duty cycle of 1.5ms (CCR1 = 1500 - 1) will rotate the axis to the center position
// the servo used was a sg90 but I guess the code will work with any servo (refer to the servo's datasheet to confirm this)

#include <msp430g2553.h>

#define SERV BIT6                       // P1.6 SERV

void main(void) {
  WDTCTL = WDTPW + WDTHOLD;             // stop WDT
  BCSCTL1 = CALBC1_1MHZ;                // submainclock 1MHz
  DCOCTL = CALDCO_1MHZ;                 

  P1DIR |= SERV;			                  // SERV pin set as output
  P1SEL |= SERV;			                  // SERV TA0.1 CCR1 output
  
  while(1){
  TACCR0 = 20000 - 1;	                  // CCR0 PWM  period 20ms
  TACCR1 = 2000 - 1;	                  // CCR1 PWM duty cycle 2ms BIT6
  TACCTL1 |= OUTMOD_7;			            // CCR1 reset/set
  TACTL = TASSEL_2 + MC_1;              // SMCLK, up mode (count up to CCR1)
  }
}