Inquiry regarding Color Saturation Issue with STM32MP257FA LTDC (RGB888) Interface

[BAEK]

I am writing to request technical assistance regarding a display issue we are encountering while developing with the STM32MP257FA. We have connected an OLED display via the LTDC interface using the RGB888 communication protocol.

[Issue Description] While the display output is functional and the image is visible, the colors appear significantly "washed out" (desaturated) compared to the original source image. It feels like some color data is being lost or attenuated.

[Troubleshooting Steps Taken] To address this, we have already performed the following debugging steps:

1. Signal Integrity: We suspected a potential issue with the R5 data line (and others) and have attempted to adjust hardware parameters, including impedance matching, trace length, and clock timing.

2. Cross-Verification: We replaced the OLED module with a new one to rule out a component defect, but the symptom remains identical.

[Attachments] For your reference, I have attached the following files:

1. Schematic: Our hardware circuit design.

2. Original Image: The source image file. (123.png)

3. Issue Photo: A photo of the actual display showing the color degradation.(20260109_114411.jpg)

Could you please advise if there are any specific configuration settings or hardware considerations we might have missed?

Additionally, I would greatly appreciate it if you could share any hardware reference design guides or application notes related to the LTDC interface for this MCU.

Best regards

[PatrickF · Accepted solution]

Hi @BAEK 

worth to share the Device Tree around LTDC, in particular the driver you use for your panel.
https://wiki.st.com/stm32mpu/wiki/Display_panels_hardware_components

https://wiki.st.com/stm32mpu/wiki/LTDC_device_tree_configuration

LTDC parallel is limited in frequency/resolution to around 150Mpixels/s (1080p 60fps), but this require good PCB, short wires.
I'm not Sw expert, but worth to verify that the LTDC GPIO are setup according to AN5489 "7.4 GPIO advance configuration".

Regards

[BAEK]

We modified the GPIO output speed settings for the LTDC interface, and it is working correctly now. We appreciate your reply.