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I'm using a LCD with a ST7701S driver and it has an 18-bit RBG interface. To control it I am using a STM32H7 with the LTDC peripheral. I have been prototyping with the STM32H745-Disco which has a LCD with a 24-bit RGB interface. To my understanding the LTDC does not offer a pixel format that is 18 bits.

Can I still use ARGB8888 or RGB888 pixel format in the LTDC with the 18-bit interface? Will I want to connect the lower or upper 6 bits of each color channel to the LCD? For example, R0-R5 of the MCU to R0-R5 of the LCD or R2-R7 of the MCU to R0-R5 of the LCD? What would the effect be of doing either of these?

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Reference Manual RM0433, Chapter 32.3.2:

For LTDC outputs up to 24 bits (RGB888), if less than 8 bpp are used to output for example RGB565 or RGB666 to interface on 16- or 18-bit displays, the RGB display data lines must be connected to the MSB of the LTDC RGB data lines.

So, yes, you can use RGB8888 and connect the upper 6 bits.

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  • \$\begingroup\$ Thank you for pointing that out! \$\endgroup\$
    – Alex Jegers
    Commented Apr 13 at 0:28

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