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TMS320F28377S: PWM: Action Qualifier submodule and shadow load

Stephane Bonnot
Prodigy 70 points

Part Number: TMS320F28377S

Hello.
I'm using ePWM to generate a specific output pattern. I use ePWM with the up-down counting. The ePWM outputs A and B change state each time the counter reaches 0 (CTR = ZRO). In the same time, I need to change the setting of these registers to generate an another pattern for the next up-down counting. To do such a thing, I use the shadow load to active register function at the same time, i.e. CTR = ZRO.
Sometimes this design does not work properly. Some unexpected ePWM output patterns appear.

I found neither in TRM nor in the Silicon errata a clear avoidance of this design.

My question is:
Should this design be avoided, prohibited or, on the contrary, authorized, proven and safe?
Thank you for your help and clarification on this point.

Stephane Bonnot

  • 0
    TI__Mastermind 27090 points

    Hi Stephane,

    I have a few questions for you so I can better understand the issue. When you say that you "generate another pattern" do you mean that you are updating the CMPA/CMPB values in an interrupt and then shadow loading those values on CTR=0? And if so, when exactly are you triggering the interrupt to happen and what values are you trying to load to the active register?

    Also, would you be able to share scope shots of the unexpected ePWM output you are seeing (and describe what you are expecting to see)? And do you see the same issue if you shadow-to-active load on CTR=PRD or CTR= PRD or 0? 

    Regards,

    Allison