Can I connect off-the-shelf DSI display to an STM32 eval board?

jhnlmn · ‎2023-08-08

I need to connect a 5 inch 480x800 display to a STM32 eval board.
There are many 480x800 DSI display on the market, but all of them are designed for PI
and have standard PI 15 pin or 22 pin connector, which has 1 clock, 2 or 4 data pairs and SCL/SDA and +3.3V.

But STM32 eval boards like
https://www.st.com/resource/en/data_brief/stm32u5a9j-dk.pdf
or
https://www.st.com/en/evaluation-tools/stm32h747i-disco.html
use some unique DSI connectors and there are no displays for them.

Question is whether it is possible to connect to STM32 a display designed for PI.

The first part of this question is whether DSI clock and data pairs are compatible.
Second is what to do with other lines on STM32 DSI connector, like:
SCLK/MCLK, LRCLK, I2S, CEC_CLK, CEC, DSI_TE, LCD_BL_CTRL, DSI_RESET, TOUCH_INT, I2C4_SDA, I2C4_SCL.
I guess I2C should be compatible, but what to do with others?
Is it possible to make some simple adapter?

Thank you

MM..1 · ‎2023-08-19

Try go back to start. You ask connect other pinout DSI to EVAL. Primary dont do it. DSI is suer high speed bus and require very perfect signal ways = every reduction ang long way is source for trouble.

For custom DSI create own custom board with STM and right connector.

Here one example 1280x480

RhSilicon · ‎2023-08-19

@MM..1 wrote:
Try go back to start. You ask connect other pinout DSI to EVAL. Primary dont do it. DSI is suer high speed bus and require very perfect signal ways = every reduction ang long way is source for trouble.

I partially agree, see this:

In theory, the CSI/DSI interface isn't meant for super long cables, and you're not supposed to extend them. But we laugh in the face of theory. We connected two 1 meter long extension cables using this Thingy and our Display and Camera worked! But, just so you know, it's really not guaranteed: CSI/DSI are meant for maybe 25cm max length.

https://thepihut.com/products/adafruit-csi-or-dsi-cable-extender-thingy-for-raspberry-pi-ada3671

MM..1 · ‎2023-08-20

I write source for trouble not impossible and maybe good is say DSI have low and high speed mode and command mode displays can only use low that dont have troubles with ...
And problem isnt lenght, but difference between lenght data and clock lanes plus changes in diferential line impedance...

jhnlmn · ‎2023-08-26

@RhSilicon Thank you for your research. But it is a bit theoretical. I have a more practical question.

I just ordered stm32u5a9j-dk and B-LCDAD-RPI1 adapter.
stm32u5a9j-dk appears to be the best and most powerful MCU-based board on the market, I would love to use it, but it has a ridiculous round display. What I am going to do with it? Roll it on the floor? use it as a hockey puck?

No, I need to buy some rectangular 480x800 5 inch display with capacitive touch panel, which I can plug to stm32u5a9j-dk and have it work right away. I do not want to buy and try all displays on the market, especially since their manufacturers said that they will not work with STM32.

I assume somebody at ST Micro did successfully test B-LCDAD-RPI1 adapter with some displays. How can we get that information?

MM..1 · ‎2023-08-26

Here is one example Raspberry Pi® RB-LCD-7 Module 17.8 cm (7 inch) 800 x 480 Pixel Compatible with (development kits): Raspberry Pi | Conrad.com

then you can see connection to display will over two adapter boards and next help wires...

And simple reply to your question is all DSI displays with 2 LANE support (respect stm speed limit) you can connect to STM. But connect to any DK or eval board will require adapter boards ... for example primary because every lcd have own pinout and secondary voltage for backlight may require stepup convert...