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PWM Deadband strange behaviour

Victor Azevedo
Intellectual 725 points

Greetings, im using a TM4C123GXL launchpad and I have a little problem in my PWM code. I'm configuring the PWM and i have it working, the problem is, when i place the PWMDeadbandEnable, the PWM value stay's on when it should be off.

void ConfigPWMPorts (void) {
ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
SysCtlPWMClockSet(SYSCTL_PWMDIV_1);
SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM1); //The Tiva Launchpad has two modules (0 and 1). Module 1 covers the LED pins
ulPeriod = SysCtlClockGet() / 8340; //PWM frequency 10kHz
GPIOPinConfigure(GPIO_PF2_M1PWM6);
GPIOPinConfigure(GPIO_PF3_M1PWM7);
GPIOPinTypePWM(GPIO_PORTF_BASE, GPIO_PIN_2 | GPIO_PIN_3);
PWMGenConfigure(PWM1_BASE, PWM_GEN_3, PWM_GEN_MODE_UP_DOWN | PWM_GEN_MODE_GEN_SYNC_LOCAL);
PWMGenPeriodSet(PWM1_BASE, PWM_GEN_3, ulPeriod);
PWMPulseWidthSet(PWM1_BASE, PWM_OUT_6,0);
PWMPulseWidthSet(PWM1_BASE, PWM_OUT_7,0);
PWMOutputInvert(PWM1_BASE, PWM_OUT_7_BIT, false);
PWMOutputInvert(PWM1_BASE, PWM_OUT_6_BIT, false);
PWMOutputState(PWM1_BASE, PWM_OUT_6_BIT | PWM_OUT_7_BIT, true);
PWMGenEnable(PWM1_BASE, PWM_GEN_3);
//PWMDeadBandEnable(PWM1_BASE, PWM_GEN_3, 100, 100);
}

if condition{

PWMOutputInvert(PWM1_BASE, PWM_OUT_7_BIT, false);
PWMPulseWidthSet(PWM1_BASE, PWM_OUT_6, ulPeriod); // PWM Period Set
PWMPulseWidthSet(PWM1_BASE, PWM_OUT_7, ulPeriod);

}

This condition is, if its true, keeps both PWM_OUT at same state and not changing, else, generate and place the deadband.

Well at least it should be, but what's happening is that if i uncoment the PWMDeadBandEnable, because i suppose it stays configured, the PWM goes to High on one port

  • 0
    TI__Guru**** 244380 points

    Hello Victor

    I am not sure but this is not a good idea to have PulseWidth as 0. Instead you can keep them as GPIO and only switch them to PWM mode when condition is true.

    PWMPulseWidthSet(PWM1_BASE, PWM_OUT_6,0);
    PWMPulseWidthSet(PWM1_BASE, PWM_OUT_7,0);

    Regards

    Amit

  • 0 in reply to Amit Ashara
    Intellectual 725 points

    I changed that to ulPeriod, because if i dont use a value at these ports, i dont know in which state they are going to stay, so this way i garantee that PWM is at maximum or minimum and doesnt change the exit.

    My problem is the DeadBand i want to implement 

  • 0 in reply to Victor Azevedo
    TI__Guru**** 244380 points

    Hello Victor

    OK. So by default you need the pair of PWM signal to be at maximum or minimum, i.e 1-0 or 0-1 but when the condition is true then the Dead Band Inserted in the changing pair of signals. Is that correct? If not, then can you please draw it out

    Regards

    Amit

  • 0 in reply to Amit Ashara
    TI__Guru**** 244380 points

    Hello Victor

    What was the issue and how did you resolve it. I may have to "Un-Verify" myself if there is not a definitive solution on the forum.

    Regards

    Amit