LCD and HDMI function of BBB

Hi everybody,

I want to ask if I can use the BBB’s LCD and HDMI function simultaneously? I have done some research through the internet and found out that the answer is yes. I am using the Ubuntu Image in which HDMI is enabled by default but I cannot capture any LCD signal. I am sorry because I don’t have a real LCD for testing. I am designing a circuit to capture LCD signals and display it. I tested capturing these signals by using signal tap of Quartus.

Hope to hear your feedback.

As long as the HDMI display and the LCD have the same exact timings and resolution. But, that i s not likely to be the case.

All the signals to the HDMI framer also go to the expansion headers at the same time.


Thank for your support, I have read from portion 12.1 of this content It said that “The onboard HDMI driver uses the LCD pins. They are still connected to the expansion header, but in some cases, they could cause an LCD cape to have some noise issues unless the cape has a buffer”. Does it cause the problem? I used signal tap to capture the positive edge of Vsync but it was not successful. I have also tried several image and the results were the same.


Vào 00:10:22 UTC+7 Thứ bảy, ngày 21 tháng chín năm 2013, Gerald đã viết:

Yes. I wrote the document. You need to make sure the signals are buffered before connecting to an LCD. More importantly, the HDMI function needs to be disabled to allow something other than 1024x768 to be sent to those pins.


Finally, I can capture these LCD signals after disabling HDMI and enabling BB-BONE-LCD4-01 firmware. Thank you very much Gerald. By the way, I want to ask another question related to LCD signals. Do these signals follow the timing described in this image ?


Vào 20:06:47 UTC+7 Thứ bảy, ngày 21 tháng chín năm 2013, Gerald đã viết:

They follow the timing that the SW tells it to follow. It is completely under SW control. So, I cannot answer if they follow the timings you reference, especially as the timings you reference do not have single timing listed on it.


Sorry Gerald, but I don’t quite understand what you said. In my question, I am using these pins with the function of LCD. I think that if we use these pin as GPIO or other functions, of course we can control it by SW. But I think that LCD signals have to follow the standard of timings to interface with other LCD cape. In my picture, there are timings of LCD signals of TFT LCD interface (as you can see, there are timings of Hsync, Vsync, data, …). Is my thinking wrong? Do you have any document related to control LCD signals by SW?


Vào 00:29:54 UTC+7 Thứ hai, ngày 23 tháng chín năm 2013, Gerald đã viết:

Yes, the signals look like LCD signals because the HW inside the processor is an LCD controller. As to changing the timings, that has been discussed many time son the forum so I suggest you do some searching there.


Can i know what changes you made in LCD4 to get the display in LCD because even im doing the same but still im not successfull…


i am using BBB and chipsee LCD expansion, i would like to know the process to connect LCD screen as well as HDMI monitor both at the same time to duplicate the screen on both?

There is only one interface, so whatever you send to one is sent to the other. The issue would be to find a resolution and timing that both the LCD and the monitor would like. That will be tough to do.


Dear Gerald,

Thank you for all your replys.
I am a novice to BBB. In one of your post it has mentioned that there is no need to disable the HDMI framer, just change the mux. It may sound silly but how to change mux ?

Please help.

Well. Search this forum as it has been talked about for years. Or you can look At the Technical reference Manual for the AM3358 processor.


Thanks Gerald, let me try.

Hi chai. I try to connect LVDS trasmitter on beaglebone black: it functions if I connect also HDMI monitor. I tried to do overlay but whitout succeed. Is there a way to do overlay whitout using EEPROM or maintain HDMI chip alway on ?

I gratefully if you explain the procedure.


I brought New beaglebone black and when I try to interface LCD to beaglebone black using HDMI cable I get ‘No signal’

Mostly first way is to enable video and cape universal in boot/uEnv.txt in sd card for debian9 image


I did it again checked and it is already included still I am getting ‘No Signal’ on LCD

Next thing I search on websites

as per their guidance for HDMI, the etc/X11 consist of the xorg.config file, but in my sd card, I didn’t see that particular file.Even on Ubuntu in /etc/X11 i see xorg.config.failsafe file instead.

I am unable to find out the reason for getting ‘No signal’ on LCD.

Is that new BBB requires setting for HDMI?