Create external signal with clock 100 Mhz in STM32H745

Ronil · ‎2024-08-21

Hi all, I have already searched on the forms and in general did not find an answer to my problem, I will be very grateful to you for help.
I need to create an output signal with a frequency of 100 Mhz as CLK in STM32H745. I used the Discovery Boards (STM32H745I-DISCO STM32H750B-DK) for the test.

1. I used timers with PWM and adjusted the ABM timer clock for 220 MHz, set up pre-scaler and counter period

But I achieve only 50 Mhz a clock as a maximum, with settings for 100 Mhz there is nothing at the output for CLK. To detect the clock I use PicOscope6404D (Bandwidth 500 Mhz).

2. I used as output ch A8 and adjusted A8 for RCC_MCO_1

I used the next settings but received the same result as for Timers not more than 50 MHz. Can you explain why I have this limitation (because the device settings show me that I can reach 100 Mhz but in real not )?

3. Finally I used the PA8 HRTIM_CHB2 timer and received high and very unstable frequency with very low amplitude. Do you how I can make a stable frequency and increase amplitude from HRTIM_CHB2?

BarryWhit · ‎2024-08-23

What does "PWM without a timer" mean? no.

The PWM signal, AFAIK, is sent out through the same output driver, and is affected by the same GPIO speed register setting.

I don't know where you get this 20Mhz figure, your OP said you were able to go as high as 50Mhz. Did you set the GPIO speed registers to a higher speed and retest?

SoftLit's screenshot shows MCO output is ~3.3 Vpp. Are you sure your measurement equipment is set up properly?

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BarryWhit · ‎2024-09-04

So after I suggested here that he needs to set the GPIO output to a higher strength, and after MasterT also suggested the same, OP started a duplicate thread - in which @TDK suggested that he needs to set the GPIO to a higher strength. Which fixed the problem.

I hate the internet. :raising_hands:

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TDK · ‎2024-09-04

@BarryWhit

Yes, frustrating. FWIW, same thing happens to me all the time. Answer the question in the very first response, and OP doesn't read it, or ignores it, or something. Sorry about that.

A screenshot showing how/where to adjust the setting can sometimes improve your chances here.

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Ronil · ‎2024-09-04

Hello, actually it is works now, sorry I missed your responses

Ronil · ‎2024-09-04

Thank you for your advice! I misunderstood your message

BarryWhit · ‎2024-09-04

@TDK, certainly nothing for you to feel sorry about.

Actually, I've probably done the same in the past - It's not malice. But yes quite frustrating for those trying to help. Just venting.

It's also been my experience that when posters get several suggestions, they tend to pick a few (usually the easiest ones) and ignore the others. Then the thread just keeps going as if those suggestions were tested but didn't work.

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Ronil · ‎2024-09-04

thank you so much, I really appreciate for your support, in the future I will be more attentive to people who helped me