PWM - phase shifting mc9s12xdp512

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PWM - phase shifting mc9s12xdp512

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kenung
Contributor I

Hello,

 

I am looking to create a phase shift of 90 degrees on two, possibly three PWM channels with a 10% duty cycle.  Can I set PWNCNTx channels in a way to accomplish this?  Thanks in advance.

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lama
NXP TechSupport
NXP TechSupport

Hi, I do not know how complex system you will drive but have you thought about XGATE and PIT channels. I believe it will provide you more variability to create signals. Moreover, if you do not use XGATE for anything more it is not affected by CPU interrupts as well as it does not affects CPU code.

Best regards,

Ladislav

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danielmartynek
NXP TechSupport
NXP TechSupport

Hi


Any value written to the PWMCNTx register causes PWM counter to be reset.

The only solution is to trigger the PWM channels by software with certain delay.

Although there is always certain latency, it works.

PWM_shift.png

For instance, the example above shows four left-aligned PWM signals, where

PWM0: Used only for generating delay.
PWM1: Original signal
PWM2: shifted (90 degree), enabled on falling edge of PWM0
PWM3: shifted (180 degree), enabled on rising edge of PWM0

PWM0 and 1 are enabled from main function at the same time. The other two signals are triggered from ISR.

Pins P6 and P7 are set for pin event detection and connected to PWM0 (Pin P0).

When falling (P7) or rising (P6) edge is detected, the ISR enables other PWM.

Therefore, the phase shift is determined by the duty cycle and the period of PMW0.

Once all shifted PWM are enabled, PWM0 may be disabled.

Please see the project attached.

I hope it helps

Daniel

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kef2
Senior Contributor IV
  • The only solution is to trigger the PWM channels by software with certain delay.

Not only. PWMCNT indeed helps.

PWMPER1 = targetperiod;

PWME = (1<<0)|(1<<1); // enable channels 0 and 1

PWMPER0 = targetperiod/2u; // 180 deg phase shift

disable_interrupts();  // prevent interrupt / taskswitching between next two lines

PWMCNT01 = 0; // reset counters 0 and 1, immediately apply period, duty, polarity etc

PWMPER0 = targetperiod; // Since PWMPER is double buffered, period will
                    // restore to full targetperiod at the end of current targetperiod/2 !

enable_interrupts();

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danielmartynek
NXP TechSupport
NXP TechSupport

Hi Edward

You are right, this is much better.

Dan

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