3.1.8 PWM

The below example demonstrates how to use the PWM peripheral to generate a PWM signal and vary the duty cycle at run time. Based on the user input on the console, the duty cycle is incremented or decremented in steps of 1% while keeping the frequency of PWM output same.

char input = 0;
int16_t onTime = 0;
int16_t offTime = 0;
float dutyCycle = 0;
uint32_t onePercDutyCycleCnt = 0;
uint32_t period;

int main ( void )
{
    /* Initialize all modules */
    SYS_Initialize ( NULL );
    
    printf("\n\r---------------------------------------------------------");
    printf("\n\r                    PWM Demo                     ");
    printf("\n\r  Press '+'/'-' to increment/decrement duty cycle by 1%% ");
    printf("\n\r---------------------------------------------------------\n\r");
    
    period = (PWM0_OnCountGet() + 1 + PWM0_OffCountGet() + 1);
    dutyCycle = ((PWM0_OnCountGet() + 1)/(float)period) * 100.0;
    onePercDutyCycleCnt = (period)/100;
       
    printf("Frequency = %ld Hz\r\n", 48000000/(period));
    printf("Duty Cycle = %2.2f%%\r\n", dutyCycle);
                
    PWM0_Start();

    while ( true )
    {
        scanf("%c", &input);
        
        if ((input == '+') && (dutyCycle <= 99.0))
        {
            dutyCycle += 1;
        }
        else if ((input == '-') && (dutyCycle >= 1.0))
        {
            dutyCycle -= 1;
        }
        
        onTime = onePercDutyCycleCnt * dutyCycle;
        offTime = period - onTime;
        
        if (onTime >= 0 && onTime <= 65535 && offTime >= 0 && offTime <= 65535)
        {
            PWM0_OnCountSet(onTime);
            PWM0_OffCountSet(offTime);
            dutyCycle = (float)(onTime + 1)/(onTime + 1 + offTime + 1);
            dutyCycle *= 100;
            printf("Duty Cycle = %2.2f%%\r\n", dutyCycle);
        }
    }

    /* Execution should not come here during normal operation */

    return ( EXIT_FAILURE );
}

Functions

Data types and constants