f28069 change pwm duty cycle

Angela Brock

Hi,

I have used the sample code found in the technical reference guide to set up pwm 1, 2, and 3. Regardless of the values chosen for CMPx the duty cycle does not alter. I have a 90Mhz clock and want a 1kHz pwm.

EPwm1Regs.TBCTL.bit.CTRMODE =2;//asymmetrical upcount
EPwm1Regs.TBPRD = 45000; // Period = 45001 TBCLK counts assumes sysclkout=tbclk=90MHz
EPwm1Regs.TBCTL.bit.PHSEN = 0; // Phase loading disabled
EPwm1Regs.TBPHS.half.TBPHS = 0; // Set Phase register to zero
EPwm1Regs.TBCTR=0;//clear counter
EPwm1Regs.TBCTL.bit.HSPCLKDIV=0;//sysclk/1
EPwm1Regs.TBCTL.bit.CLKDIV=1;//sysclk/2

EPwm1Regs.CMPA.half.CMPA = 4500; //duty cycle
EPwm1Regs.AQCTLA.bit.PRD = 2; //EPWMA output high when counter equals the period
EPwm1Regs.AQCTLA.bit.CAU = 1; //EPWMA output low when counter equals CMPA on up count

over 9 years ago

0 Richard Poley over 9 years ago

TI__Mastermind 27200 points

Angela,

Nothing is obviously wrong with the code. Are you saying you can get a PWM output but the the duty cycle is wrong, or that the CMPA register has the wrong value?

Regards,

Richard

0 Angela Brock over 9 years ago in reply to Richard Poley

Intellectual 480 points

I have a pwm output, but the duty cycle is 50%. The first 4 hex values of the union of CMPA and CMPAHR show 4500. TBPRD shows 45000. This should be a 10% duty.

Also, I hooked this code up to the scope and am only getting a 500Hz reading when I am looking for a 1kHz pwm.

0 Todd Anderson78572 over 9 years ago in reply to Angela Brock

Guru 14640 points

processors.wiki.ti.com/.../C2000_Archived_Workshops

Module 7 - control peripherals does a good job of teaching the PWM on F28069.

0 Richard Poley over 9 years ago in reply to Todd Anderson78572

TI__Mastermind 27200 points

Angela,

I think the problem is you have configured the time-base in symmetrical (up-down count) mode, rather than the symmetrical (up-count) mode indicated in the comment of the first line of code. Based on the AQ settings, and the compare value, I think you should be seeing a 500Hz PWM frequency with 60% duty cycle.

Try changing the first line to

EPwm1Regs.TBCTL.bit.CTRMODE = 0;

Regards,

Richard

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f28069 change pwm duty cycle