Is 48MHz PWM possible using SCT on LPC4357@204MHz?

quex — Wed, 13 Jun 2018 13:25:24 GMT

I'm currently struggling with the SCT, which I need to use for PWM generation.

I tried the LPCopen function:

Chip_SCTPWM_SetRate(LPC_SCT_T *pSCT, uint32_t freq);

It calculates a rate and writes it to the match reload register 0:

rate = Chip_Clock_GetRate(CLK_MX_SCT) / freq;

Chip_SCT_SetMatchReload(pSCT, SCT_MATCH_0, rate);

The chip clock is 204MHz and the requested PWM frequency (freq) is 48MHz.

204 / 48 = 4.25

The decimals are of course lost and I end up with a frequency of 40.8MHz (204 / (4+1))

The next step I can reach using this function is 51MHz.

Is there a way to get 48MHz output frequency using directly the SCT registers, without LPCopen?

Thanks for any hint.

Edit:

The frequencies are not multiples, the clock can only be divided, there is only one internal clock source for SCT.
It's not possible to generate PWM @ 48 MHz.

Re: Is 48MHz PWM possible using SCT on LPC4357@204MHz?

kerryzhou — Fri, 15 Jun 2018 04:33:17 GMT

Hi quex,

Yes, just as your edit content.

Because 204/48=4.25, it not multiples, then you can't generate the 48Mhz directly.

If you want to generate the 48Mhz, I think you need to change the SCT module clock, which can be muliple by 48Mhz.

Wish it helps you!

Have a great day,
Kerry

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

topic Is 48MHz PWM possible using SCT on LPC4357@204MHz? in LPC Microcontrollers

Is 48MHz PWM possible using SCT on LPC4357@204MHz?

Re: Is 48MHz PWM possible using SCT on LPC4357@204MHz?