question about PWM / Full compare

Jason Reinhart

Other Parts Discussed in Thread: TMS320F2812

Hi,

I'm trying to use PWM1/2 on my TMS320F2812 to generate two PWM signals with a 50kHz carrier.

My DSP is running at 150MHz. From what I can tell, since the full compare module uses timer 1 as the time base, the lowest PWM frequency I can generate would be 585.9375kHz, (hspclk/128, where hspclk=sysclk/2=75MHz).

Is this correct? Is there some other way to further divide timer1 down to get the carrier frequency of 50kHz that I need?

Thanks,

Jason

over 16 years ago

0 Daniel Chang over 16 years ago

TI__Expert 4120 points

Hi Jason,

What do you mean by "full compare module"?

Regards,
Daniel

0 Jason Reinhart over 16 years ago in reply to Daniel Chang

Intellectual 435 points

Sorry, I mean "Full Compare Units". As in, I'm trying to use compare units 1 and 2 in the EVA module to generate PWM1 and PWM2 outputs.

0 Arefeen over 16 years ago

Genius 5170 points

The PWM frequency is set by the timer period and the timer is run by system clock as you described. If you input 75Mhz clock to run your PWM timer then in order to generate a PWM frequency of 50KHz the period register should be loaded with 1500 (75MHz/50KHz ). By the way, there is also prescalar to further slow down your timer clock but that will lower your PWM resolution. There are multiple example projects showing how to generate PWM outputs.

0 Jason Reinhart over 16 years ago in reply to Arefeen

Intellectual 435 points

OK. Wasn't clear to me in the Event Manager Guide whether that T1PR sets the PWM carrier. Thanks

Just curious, where do find examples? I have Example_281xEvPwm that's in my code composer directory but it's a little vague to me.

0 Daniel Chang over 16 years ago in reply to Jason Reinhart

TI__Expert 4120 points

Have you tried the header files and peripheral examples package?

You can find it here:
F281x C/C++ Header Files and Peripheral Examples

http://focus.ti.com/mcu/docs/mcuprodtoolsw.tsp?sectionId=95&tabId=1222&familyId=916&toolTypeId=1&DCMP=DSP_C2000&HQS=Other+OT+f28xkits#swtools

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question about PWM / Full compare