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Async Trip Zone PWM shut-off

James McLaughlin
Expert 1090 points

Other Parts Discussed in Thread: TMS320F28069

I'm attempting to use the external trip-zone behavior to shut off several PWMs as soon as the trip event occurs.  I am using TZ1, TZ2 and TZ3 on a TMS320F28069 device.  The green trace on my screenshot is the TZ pin (shorting to ground for event), and the yellow trace is my output PWM (at just shy of 100% so the periods can be seen).

What I'm observing is that there is a 1-2 PWM period delay for the full shut-off to occur (depending on when the error occurred within the period).  It seems to successfully shut off for about 1us, but then turns back on for another period or two.  My PWM period is 5us.

According to page 291 of TMS320x2606x Piccolo - Technical Reference Manual (spruh18c - april 2011), there should be an asynchronous path for the TZ event to follow to shut off PWMs.  I don't see any register for the Trip Zone hardware that sets this option, so I'm not sure if it's following it or not.  It appears that it might be, due to the first ~1us of shut-off time.

These are all configured for OSHT events (not cycle-by-cycle), Gpio qualification is set to async on the TZ pins used, and the OSHT interrupts/events are not cleared until the PWM is shut off manually.

Is there something I'm missing?  Other places I can look?

Thanks.

- James

  • 0
    Expert 1090 points

    My mistake.  In my TZ interrupt I was actually resetting the TZA action in TCZCTL to 0 (no action) before I set the PWM CMPA register to 0.

    If anyone can shed some light on the sync vs async option for TZ signals I referred to in the previous post, however, that would be helpful ("Trip-Zone Submodule Mode Control Logic" on page 291 of the technical reference manual).  Thanks.

    - James