Can I use GPIOs as the PWM signal output? 28377D

Javy ZHANG

Hi everyone,

I wonder if I can generated PWM signals from the GPIOs in 28377D.

I tried to realized this but the frequency couldn't go up further.

I created a signal using Simulink and configured GPIO 35 (pin 121) as the output pin. If the period of created signal is above 20 us (50 kHz) then it worked well, i.e. the output signal from GPIO 35 was exactly same as the created one. But when I reduced the period of the created signal to 10 us (100 kHz) then the signal obtained from the GPIO 35 remained 20 us (50 kHz). I tried many times and tried to reload the program.

I wonder if there is any limitation on the GPIO output frequency?

The problem behind this is:

ePWM is essentially duty cycle based signal generation. I want to realize the on/off (0/1 or 3.3/0) based signal generation. So I tried to configure GPIO as the PWM output ports.

Thanks for any help in advance.

Javy

over 8 years ago

0 Vivek Singh over 8 years ago

TI__Guru** 113515 points

Hi,

You should be able to toggle the GPIO output at much higher frq (@MHz rate). How are you controlling the GPIO toggle frq in your code?

Regards,

Vivek Singh

0 Javy ZHANG over 8 years ago in reply to Vivek Singh

Intellectual 525 points

Hi,

Thanks for the prompt reply.

I am using Matlab/Simulink to create the signals. I just used a pulse generator block from Simulink and I set the period to 10 us (100 kHz) and connected to GPIO 35.

Javy

0 Javy ZHANG over 8 years ago in reply to Javy ZHANG

Intellectual 525 points

Hi,

I noticed that the toggling frequency of GPIOs can be as high as 25 MHz. But I couldn't figure out the reason why it was clapped to 50 kHz. what do you think could be the reason behind this?

Thanks,
Javy

0 Vivek Singh over 8 years ago in reply to Javy ZHANG

TI__Guru** 113515 points

I am suspecting some missing configuration or updated code is not getting loaded and old code is still running. Could you compare both the code and check the difference?

Regards,

Vivek Singh

0 Javy ZHANG over 8 years ago in reply to Vivek Singh

Intellectual 525 points

The only difference is the period: 20us and 10 us.

Cheers,
Javy

0 Mark Labbato over 8 years ago in reply to Javy ZHANG

Guru 30330 points

Javy,

what method are you using to toggle the GPIOs? Are you using Single register writes or the GPIOWrite() function? Single register writes directly to the GPIOSET/CLEAR registers will give you the best performance. GPIOWrite() needs to decode the GPIO which you would like to write to, and this will take some number of clock cycles to do.

Thanks,

Mark

0 Javy ZHANG over 8 years ago in reply to Mark Labbato

Intellectual 525 points

Hi Mark,

Thank you for you reply.

To be honest, I don't know what register write method is that coz I am using Matlab/Simulink based code generation. There is nothing about register write configuration.

Cheers,

Javy

0 Brian McKay over 8 years ago

Mastermind 9005 points

It might be possible that the model is overrunning.

I'd suggest contacting MathWorks Technical Support for assistance on how to measure and debug this.

You can also try to run the example model c28027pmsmfoc_ert.slx and see if that has the same issue. Doc page for that example (login may be required).

-Brian

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Can I use GPIOs as the PWM signal output? 28377D