CCS/TMS320F28379D: Question about Lab 3 Tutorial

Kevin Bachovchin

Tool/software: Code Composer Studio

I'm a newbie trying to learn to program TI microcontrollers, so I apologize about the simple question.

I'm going through the C2000™ MCU 1-Day Workshop

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwj8-LfftJDoAhVtQt8KHYotDhcQFjAAegQIAhAB&url=https%3A%2F%2Fe2echina.ti.com%2Fcfs-file%2F__key%2Ftelligent-evolution-components-attachments%2F00-56-01-00-00-38-69-26%2FC28x_5F00_Microcontroller_5F00_ODW_5F00_2_2D00_0.pdf&usg=AOvVaw2U14s7h81LaVnWkOVk-gMx

For the Lab 3 exercise (page 83 of the PDF with the above link), in step 26 it says "Finally set the variable period1 to 75000. What happened and why?"

When I do this, what happens for me is that the PWM output flatlines and is no longer a PWM signal. However, I don't understand why this is happening. I would expect that it would just make the PWM period longer. Is there some maximum value that the PWM period can be set to and exceeding this value causing the PWM output to flatline?

Any help would be greatly appreciated.

Thanks,

Kevin

over 6 years ago

0 Ken Schachter over 6 years ago

TI__Genius 17315 points

Kevin,

The ePWM module period register is 16-bits wide and the maximum value that can be set is 0xFFFF (65,535). This information can be found in the F28379D Technical Reference Manual:

http://www.ti.com/lit/spruhm8

Also, you might be interested in the full version of the workshop, which can be found at:

https://training.ti.com/c2000-f2837xd-microcontroller-workshop?context=1137791-1137781

You are currently using the condensed version. This version includes a video and the link can be found on the above page (see "Condensed Workshop Version with Video"). To learn more about the e-PWM module consider watching "Getting Started with the C2000 ePWM Module" at:

https://training.ti.com/getting-started-c2000-epwm-module

I hope this helps. If this answers your question, please click the green "Verified Answer" button. Thanks.

- Ken

0 Kevin Bachovchin over 6 years ago in reply to Ken Schachter

Expert 1060 points

Ken,

Thanks for your answer and the helpful links. That makes sense about the maximum value being 65,535 since it is 16 bit.

One question I still have though is what actually happens to the period when the user enters a value above 65,535? The compiler obviously doesn't throw an error. So does the number wrap around? For example, if the user enters a value of 75,000, is the effective value of the period 75000-65535=9465?

Thanks,

Kevin

0 Ken Schachter over 6 years ago in reply to Kevin Bachovchin

TI__Genius 17315 points

Kevin,

The value will wrap around in the register. The value is actually 9,464 (0x24F8), not 9465 - as you know, engineers start counting with '0'. :-)

You can see this happen when running the lab exercise. Open the 'Register' tab, or if needed View -> Registers. Make sure that the window is enabled for continuous refresh. Now, change the period value in the Expressions window and you will see the change in the Registers window. Notice that when you set period1 to 75000, the EPwm1Regs -> TBPRD value in the Registers window is 0x24F8.

I hope this helps. If this answers your question, please click the green "Verified Answer" button. Thanks.

- Ken

0 Kevin Bachovchin over 6 years ago in reply to Ken Schachter

Expert 1060 points

Ken,

Thanks again, your answers are very helpful. Do you by any chance know what might be causing my problem in the following thread?

https://e2e.ti.com/support/microcontrollers/c2000/f/171/p/888657/3285843#3285843

Thanks,

Kevin

0 Ken Schachter over 6 years ago in reply to Kevin Bachovchin

TI__Genius 17315 points

Kevin,

I have already replied to your other thread. No worries, all question concerning the device hands-on workshops will be directed to me. I will close this thread.

- Ken

C2000™︎ microcontrollers

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CCS/TMS320F28379D: Question about Lab 3 Tutorial