topic Square wave output with variable frequency, FTM in S32K

Square wave output with variable frequency, FTM

christofferjärl — Wed, 19 Jun 2019 17:15:19 GMT

Need some help to set up one FTM Ch to be able to output constant 50% DC PWM, with at run time variable frequency.

Target; 1Hz - 500Hz

Using SDK, S32K144.

Any suggestions?

Thank you!

/ Chris

Re: Square wave output with variable frequency, FTM

jorge_a_vazquez — Mon, 24 Jun 2019 17:42:40 GMT

Hi Chris J

There is already an example that can do this in the SDK that comes with the S32DS, you can find it as ftm_pwm_s32k144. Please check it and don't hesitate to tell me if you have any question about it.

Have a great day,
TIC

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Re: Square wave output with variable frequency, FTM

christofferjärl — Mon, 24 Jun 2019 18:03:24 GMT

Hi Jorge!

I have looked into this example and as far as i can see it is set up to

increment or decrement duty cycle
Update channel duty cycle
Wait for a number of cycles to make the change visible

I have tried to use the FTM_DRV_UpdatePwmPeriod() function to just change the period/frequency and keep the DC at 50%.

But I seeing some trouble to keep a clean 50%DC while changing period. I think I have some kind of timer sync problem..?

Re: Square wave output with variable frequency, FTM

jorge_a_vazquez — Tue, 25 Jun 2019 21:19:49 GMT

Hi Chris J

You have to update the Duty cycle too, because it has to be recalculated with every change in the period, so you need something like:

FTM_DRV_UpdatePwmPeriod(INST_FLEXTIMER_PWM1, FTM_PWM_UPDATE_IN_TICKS, new_period, true);
FTM_DRV_UpdatePwmChannel(INST_FLEXTIMER_PWM1, 0U, FTM_PWM_UPDATE_IN_DUTY_CYCLE, 0x4000U, 0U, true);‍‍

Hope this helps

Regards