TMS320F28069: Sync and Async in Trip zone

Ashwin Balaji AR

What would be the difference between synchronous & asynchronous to clock mean in trip zone? Here it is mentioned as "The trip-zone signals may or may not be synchronized to the system clock (SYSCLKOUT) and digitally filtered within the GPIO MUX block. A minimum of 3*TBCLK low pulse width on TZn inputs is sufficient to trigger a fault condition on the ePWM module. If the pulse width is less than this, the trip condition may not be latched by CBC or OST latches. The asynchronous trip makes sure that if clocks are missing for any reason, the outputs can still be tripped by a valid event present on TZn inputs ."

Should we take it like configuring as Asynchronous will also check for 3*TBCLK or is it completely independent of clock?

over 2 years ago

+1 Allison Nguyen over 2 years ago

TI__Mastermind 25480 points

Hi Ashwin,

The "synchronous" vs "asynchronous" terminology here is in reference to the sampling of the GPIO signal. Synchronization mode means the GPIO signal is sampled using SYSCLK whereas asynchronous refers to when the peripheral itself (in this case, EPWM) does the synchronization. A good section of the device TRM to reference for more details here would be section 1.4.4.1 and 1.4.4.2. I think you would also find Figure 1-64. Input Qualifier Clock Cycles very helpful as a good visual on how the GPIO signal sampling works!

The ePWM trip zone (TZn) signals can function independent of the presence of SYSCLKOUT (asynchronously), which is important in making sure that the trip can occur even if the SYSCLKOUT fails in some way since TZ is often used in system to stop outputs if a fault (e.g. short circuit, over-current or some other event) occurs. To function independent of SYSCLKOUT, the TZ module relies on the EPWM TBCLK, and with this there is a kind of signal input qualification (such as seen in the figure I mentioned above) where the TZ input low signal must last at least 3 TBCLK pulse widths to be recognized as a "trip" and successfully trigger a response by the TZ module. Keep in mind TBCLK is just a prescaled version of the system clock defined when EPWM is set up. So the GPIO can be synchronous or asynchronous as defined in the GPIO registers, but the trip event itself will not rely on the SYSCLKOUT but TBCLK. Hope this helps! Let me know if you have further questions here.

Regards,

Allison

0 Ashwin Balaji AR over 2 years ago in reply to Allison Nguyen

Prodigy 50 points

Thanks Allison Nguyen for the clarification.

0 Ashwin Balaji AR over 2 years ago in reply to Allison Nguyen

Prodigy 50 points

Hey Allison Nguyen,

By any way this 3 TBCLK can be extended? Like 100/200 TBCLK's or if the window can be multiplied over a certain ZERO to TBCLKPRD

The application I need this for is very similar as found in this thread. Filtered glitch issue in PWM Digital Compare Module. Wherein the glitch can occur at any window with 200 clock cycles wide. Let's say it is present only for 100 cycles then I'll have to ignore it as a false signal.

+1 Allison Nguyen over 2 years ago in reply to Ashwin Balaji AR

TI__Mastermind 25480 points

Hi Ashwin,

The device TRM section 3.2.7.3 Operational Highlights for the Trip-Zone Submodule states that the GPIOs can be used to digitally filter the signals:

And if you go to TRM section 1.4.4.3 Qualification Using a Sampling Window:

Please refer to this GPIO input qualification section- you would be able to filter the GPIO signal via sample freq and number of samples in the GPIO mux before the signal is sent to the EPWM TZ module. Would this work for what you are trying to accomplish?

Best regards,

Allison

0 Allison Nguyen over 2 years ago in reply to Allison Nguyen

TI__Mastermind 25480 points

I realize I was referencing the Trip Zone submodule in my reply, but you were referring to using the Digital Compare submodule- just wanted to clarify that this same principle can apply to the Digital Compare submodule since the signals pass through GPIO mux (and can be filtered there) before entering Digital Compare!

0 Allison Nguyen over 2 years ago in reply to Allison Nguyen

TI__Mastermind 25480 points

Closing this thread to continue conversation on another thread: https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/1290985/tms320f28069-digital-compare-unit---sampling-of-signal

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TMS320F28069: Sync and Async in Trip zone