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Generating 50Hz 0-100% Duty Cycle PWM Waveform using Timer_A

Timothy Batlogile
Prodigy 60 points
Other Parts Discussed in Thread: MSP430F2011, MSP430G2452

#include <msp430f2011.h>
#define _XTAL_FREQ 20000000
unsigned int width=0;
void main(void)
{
WDTCTL = WDTPW + WDTHOLD; //turn off the watch dog timer
DCOCTL = CALDCO_16MHZ; //set internal clock speed to 16 MHz
BCSCTL1 = CALBC1_16MHZ; //set internal clock speed to 16 MHz
P1DIR = BIT6;
P1SEL = BIT6;         //TA1
TACCR0 = 40000;    //2000000/40000 = 50hz = 20ms
TACCTL1 = OUTMOD_3; //set/reset
TACCR1 = width; //1.5ms pulse
TACTL = TASSEL_2 + MC_1 + ID_3; //up mode, SMCLK/8

while(1)
{
if(width<40000)
{
width = width+1;
}
else
{
width = 0;
}
TACCR1 = width;
__delay_cycles(100);
}
}

I need help with this PWM  code,it produces a straight line in proteus simulation, maybe there is a problem with the while loop. 

  • 0
    Guru 192875 points

    Hi Timothy,

    Your logic seems to be fine but I've a doubt with your implementation. Have you gone through the sample codes? Try with them and try editing the same using this logic!

    Regards,

    Gautam 

  • 0
    Expert 1620 points

    Timothy Batlogile said:


    #define _XTAL_FREQ 20000000

    Where do you get 200 000 000?

  • 0 in reply to Joseph Raslavsky
    Prodigy 60 points

    I used an external crystal oscillator of 20MHz at P2.7  and P2.6 and even after removing it i'm still not getting a PWM 

    How do i declare this 

    P1DIR = BIT6;
    P1SEL = BIT6; //TA1

    in this form

    P1DIR |=0x**;
    P1SEL |=0x**;  //TA1

  • 0 in reply to Timothy Batlogile
    Prodigy 60 points

    I managed to fix it,here is the complete CODE

    //Generating 50Hz 0-100% Duty Cycle PWM Waveform using Timer_A
    #include "msp430x20x1.h"
    int main(void)

    {

    WDTCTL = WDTPW + WDTHOLD; //turn off the watch dog timer

    DCOCTL = CALDCO_16MHZ; //set internal clock speed to 16 MHz

    BCSCTL1 = CALBC1_16MHZ; //set internal clock speed to 16 MHz


    P1DIR |= 0x0C;
    P1SEL |= 0x0C; //TA1

    TACCR0 = 40000; //2000000/40000 = 50hz = 20ms
    TACCTL1 = OUTMOD_3; //set/reset
    TACCR1 = 37000; //1.5ms pulse
    TACTL = TASSEL_2 + MC_1 + ID_3; //up mode, SMCLK/8

    while (1){

    }

    }

  • 0 in reply to Timothy Batlogile
    Guru 16361 points

    Hi Timothy,

    I tried your original code on an msp430g2452 installed in a launchpad and it worked fine. The green LED connected to P1.6 dimmed from 100% brightness to 0%, then jumped back to 100%. Each PWM cycle took about 0.25s. I'm not sure why it didn't work in your case.

    The code in your last post doesn't appear to do a PWM sweep, it just outputs a fixed duty cycle. Did the forum software lose the contents of the while loop?

    Rob

  • 0 in reply to Robert Cowsill
    Prodigy 60 points

    Hi Rob 

    I removed the while loop because it was giving me errors when compiling.

    So I used the code without the while loop since i'm  doing the proteus simulation only a fixed duty cycle will do as you can see below

  • 0 in reply to Timothy Batlogile
    Prodigy 10 points
    Hi Timothy I am also finding hard to generate pwm in msp430 67791a help in this.

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