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LTDC CLK for 16bit RGB on a STM32L4+ having issues where there is a vertical line on the display.

Forum|Forum|5 years ago
March 16, 2021
4 replies
2362 views

The vertical Line seems to go away when I put a my finger on the LTDC CLK pin. I adjusted the clock frequency to above the minimum (12.5MHz) required for the display, and it still appears. I then added a 40k pulldown resistor to the LTDC CLK pin, and it went away, but I don't see any information anywhwere regarding the addition of the pulldown is an ok solution. I have read another post about the exact same issue, but the issue was closed out with no solution. Any help is greatly appreciated.

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Best answer by APesi.1

Thanks for the Suggestions! We found a Fix!

Before the fix the LTDC CLK looked like:The line GPIO_InitStruct.Speed = GPIO_SPEED FREQ_MEDIUM (5 to 25MHz) was originally set to GPIO_InitStruct.Speed = GPIO_SPEED FREQ_LOW (0 to 5MHz).

After the code change:

Still has some ringing in the clock, but its working much better.

Thanks for the suggestions.

Tesla DeLorean

Guru

>> but I don't see any information anywhere regarding the addition of the pulldown is an ok solution.

Probably not really addressing the problem.

Seems to be more of a display side issue. What does the signal look like on a scope?

If it has a lot of ringing or overshoot, you might want to consider a series resistor, or look at dropping the slew-rate (SPEEDR) of the GPIO pin.

Tips, Buy me a coffee, or three.. PayPal Venmo (See Profile) Up vote any posts that you find helpful, it shows what's working..

I

Imen.D

ST Technical Moderator

Hello @APesi.1 ,

It seems the issue is with your code/configuration.

I would suggest adding more details about your configuration, so that Community users can help you.

Imen

In order to give better visibility on the answered topics, please click on 'Best answer' on the reply which solved your issue or answered your question. Thanks

APesi.1AuthorBest answer

Associate

Thanks for the Suggestions! We found a Fix!

Before the fix the LTDC CLK looked like:The line GPIO_InitStruct.Speed = GPIO_SPEED FREQ_MEDIUM (5 to 25MHz) was originally set to GPIO_InitStruct.Speed = GPIO_SPEED FREQ_LOW (0 to 5MHz).

After the code change:

Still has some ringing in the clock, but its working much better.

Thanks for the suggestions.

I

Imen.D

ST Technical Moderator

Thank you for your update.

Glad to know that the issue is solved :smiling_face_with_smiling_eyes:

In order to give better visibility on the answered topics, please click on 'Best answer' on the reply which solved your issue or answered your question. Thanks

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