topic Re: how is pwm frequency setting parameters? in S32K

how is pwm frequency setting parameters?

rlaxortn — Tue, 13 May 2025 05:49:36 GMT

i know pwm frequency is PWM frequency = CORE_CLK / global prescaler / internal prescaler / (B1+1).

but don't understand how is set that parameter.

this pics are my current pwm frequncy setting.

i am using CH4(emios0).

and i got pwm frequency is 3.906kHz.

i wanna set pwm frequency is 30kHz.

i think CORE_CLK is 160Mhz, global prescaler is 1. internal prescaler is 1??? b1 is 32768.

so i expect pwm frequency is 160000000/1/1/(32768+1) = 4.882Khz.

1. how i set parameter for getting 30Khz pwm parameter???

2. what is mean 0x5000 in Emios_Mcl_Ip_SetCounterBusPeriod function parameter?

i changed smaller than 0x5000 value like 0x1000.

then pwm frequency is changed more higher(3.906kHz->19.53Khz).

what is mean that value and what influence that value for pwm frequency formula?

Re: how is pwm frequency setting parameters?

PetrS — Tue, 13 May 2025 10:27:47 GMT

Hi,

PWM frequency equation differs depending mode selected. For MCB up/down counting mode, the counter bus period is global prescaler * internal prescaler * (2*period_in_ticks-2) / CORE_CLK. For the init setting from picture it gives PWM freq = 160e6/1/1/(2*16385-2) = 4.882KHz you calculated. You measure 3.9kHz, as MCB period is changed in code from default one. If you stop the code after init functions and have eMIOS FRZ bit cleared you will see 4.882KHz

1. for 30KHz PWM in OPWCMB mode you need to set MCB channel's period to period_in_tics = (CORE_CLK / global prescaler / internal prescaler / 30e3 + 2) / 2. It gives 2667.66. Using 2667 value, it results in 30.0075 kHz.

2. third parameter in Emios_Mcl_Ip_SetCounterBusPeriod determines value directly written to MCB channel A register. A register specifies the MCB period and for up/down mode it will be 160e6/1/1/(2*0x5000-2) =3.906 kHz
For 0x1000 value used it is 160e6/1/1/(2*0x1000-2) = 19.536 kHz

BR, Petr

Re: how is pwm frequency setting parameters?

rlaxortn — Wed, 14 May 2025 01:14:51 GMT

@PetrS

after i watched your post, i tried.

but result is different.

when i apply Emios_Mcl_Ip_SetCounterBusPeriod(pwmInstance0, pwmCH23, 0x14d5).

i got pwm frequency is 30kHz.

so i think formula is core_clk / Period.

bacause i changed code Emios_Mcl_Ip_SetCounterBusPeriod(pwmInstance0, pwmCH23, 0x29aa). so i got pwm frequency is 15kHz.

i don't understand. because it is different with formula you teached.

and current pwm setting is same with post pics.

thanks.

Re: how is pwm frequency setting parameters?

PetrS — Wed, 14 May 2025 08:32:29 GMT

Hi,

this my measurement using RTD500

BR, Petr

Re: how is pwm frequency setting parameters?

rlaxortn — Wed, 14 May 2025 09:12:00 GMT

Re: how is pwm frequency setting parameters?

PetrS — Wed, 14 May 2025 11:53:21 GMT

Hi,

I see calculation and measurement aligned

BR, Petr

Re: how is pwm frequency setting parameters?

rlaxortn — Thu, 15 May 2025 05:41:01 GMT

@PetrS

when i set Emios_Mcl_Ip_SetCounterBusPeriod(pwmInstance0, pwmCH23, 2667);.

i got pwm frequency 60Khz.

Re: how is pwm frequency setting parameters?

PetrS — Thu, 15 May 2025 10:40:51 GMT

Hi,

it could be if channel is using counter bus in MCB up counting mode. But for channel in OPWMCB mode using counter bus in MCB up/down counting you should not get that. Unless different value is written to counter bus A register, you can check it within debugger.

BR, Petr