How to output 50Hz PWM signal on KV11Z

[le27]

Hello, I am using KV11Z and using the example ftm_simple_pwm. In the example, 24kHz can make the LED gradually brighter and darker. I want to output a 50Hz PWM modification signal.

So, I tried to change the frequency to 50Hz, but I didn't get any signal when I used the dialogue.

Want to know where is the problem?

thanks,

[Robin_Shen · Accepted solution]

Hi le27,

Peripherals tool can help know what is the suitable value of prescaler.

You shall get error by using kFTM_Prescale_Divide_1 of FTM_GetDefaultConfig. Please change the prescale :
config->prescale = kFTM_Prescale_Divide_32;

Best Regards,
Robin
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[le27]

Thank you for your reply and guidance. I followed the method and modified config->prescale = kFTM_Prescale_Divide_1 to config->prescale = kFTM_Prescale_Divide_32; directly in the file of fsl_ftm.c. It can be observed that the LED on the control board changes gradually according to the change of duty_cycle Bright and gradually dimming, there is no problem, and the PWM output signal with a frequency of 50 Hz can be reached through the oscilloscope.

Then try to add ftmInfo.prescale = kFTM_Prescale_Divide_32; to the file of ftm_simple_pwm. I want to set the prescale from this, but maintain config->prescale = kFTM_Prescale_Divide_1 in the fsl_ftm.c file; the execution result shows that no PWM signal is generated, which is not clear. Is there a mistake in the use of the program?

At present, i am also trying to modify the program to achieve a fixed frequency and adjustable duty cycle PWM output signal.

Thanks,

[Robin_Shen]

The arrow in my picture is a bit misleading.
Please put  ftmInfo.prescale = kFTM_Prescale_Divide_32; between FTM_GetDefaultConfig and FTM_Init

[le27]

Hi Robin
Now it is possible to generate a PWM signal, but encountered it again.
Set to 50Hz PWM frequency, it is only 71Hz from the observation.

I don't know why the 50Hz PWM signal is not generated. I think this is caused by the delay. I go to DELAY place to modify it. From the original 80,000 to 115400, the KV11Z development board can be generated from the file is a 10M crystal oscillator, calculate i=1 =0.1us, the direction is estimated to be 115400 by trial and error, and set the fixed duty cycle to 50%.

Finally, the required Hertz PWM signal and duty cycle can be obtained. But I still don't know if this is the correct way. I think it should only be necessary to adjust FTM_SetupPwm (BOARD_FTM_BASEADDR, &ftmParam, 1U, kFTM_CenterAlignedPwm, 50U, FTM_SOURCE_CLOCK); the PWM frequency value in this row can be used to obtain the desired PWM frequency.
I need help in this regard, thank you.

[myke_predko]

@le27 

Do you ever check the results of "FTM_SetupPwm"?  First off it has a number of asserts which may cause the application to hang without any kind of indication.  Secondly, "FTM_SetupPwm" may return an error value but continue executing as if there wasn't a problem.  

I believe the most likely error will be that FTM_SetupPwm is returning an error code because the calculation done by "FTM_SetupPwm" for 50Hz results in values which can't be generated by the hardware.  

That's a very low speed - you're probably going to have to create your own PWM using a timer.  

Good luck!

[le27]

The program continues as you said, as if no error has occurred, and no signal is generated through the oscilloscope. This time, a problem that requires frequency setting prescale has been discovered.
Thank you for your blessing and reply.