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Published 20 hours ago • verified publisher icon lvgl

Support for displays without DC pin?

Open Rajssss opened this issue 3 years ago • 10 comments

In menuconfig, there is a option to enable or disable the DC. However I beleive none of the drivers implemented it. Having such functionality will improve the usability of the driver, saving one more pin, and support Displays modules with no DC pin exposed. Even though, I had hard time finding a driver which works without a DC pin, but found some hints to a 9-Bit SPI mode?

Rajssss avatar Jun 27 '21 03:06 Rajssss

Hi,

I think you have the ST7735S display, isn't? Can you test this branch? https://github.com/lvgl/lvgl_esp32_drivers/tree/feat/support_no_dc

If this works we could start adding support on all other drivers.

C47D avatar Jun 30 '21 00:06 C47D

I will and let you know.

Rajssss avatar Jun 30 '21 03:06 Rajssss

The changes in that branch doesn't take into account the fact that the DC signal tells the display if the bytes it's getting from the MCU are a command or data.

C47D avatar Jun 30 '21 04:06 C47D

@C47D sorry it isn't working, getting garbage on the screen.

Rajssss avatar Jul 01 '21 14:07 Rajssss

I guess that's expected, the DC signals lets the display know if the data is a data or a command, what display are you working on? Could you share me an image of the connection?

C47D avatar Jul 01 '21 15:07 C47D

I guess that's expected, the DC signals lets the display know if the data is a data or a command, what display are you working on? Could you share me an image of the connection?

Yes, but with DC pin selected it works fine as expected. Here the display I have: http://www.lcdwiki.com/1.44inch_SPI_Module_ST7735S_SKU:MSP1443 And this is the pinout I am using.

photo_2021-07-02_08-40-18 Screenshot_2021-07-02_08-41-36

Rajssss avatar Jul 02 '21 03:07 Rajssss

You just answered it, the display needs the DC signal to work, you can't use it without it.

C47D avatar Jul 02 '21 14:07 C47D

You just answered it, the display needs the DC signal to work, you can't use it without it.

I don't get it. Are you saying that the display I have can not work without the DC pin? exactly what I am trying to achieve? And is it because the DC pin is exposed in the module?

Rajssss avatar Jul 02 '21 15:07 Rajssss

I don't get it. Are you saying that the display I have can not work without the DC pin?

Yes, I think so, your project works with the DC signal and it doesn't work without it.

And is it because the DC pin is exposed in the module?

Yes.

The only displays I think work without DC signal are the I2C based ones.

C47D avatar Jul 07 '21 02:07 C47D

I don't get it. Are you saying that the display I have can not work without the DC pin?

Yes, I think so, your project works with the DC signal and it doesn't work without it.

And is it because the DC pin is exposed in the module?

Yes.

The only displays I think work without DC signal are the I2C based ones.

Unfortunately, I don't have one. maybe in future someone will test it. I have found a thread on a display without DC pin exposed, using 9Bit SPI but for ILI9341, can you take a look? https://forum.arduino.cc/t/how-to-wire-ili9341-in-spi-without-d-c-pin/

Rajssss avatar Jul 07 '21 03:07 Rajssss