BBB won't boot when LCD is connected

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1

Hello, Everyone.

I am in the very early stages of interfacing the BBB with a new 4.3" TFT LCD, not a cape. It has a 16-bit data bus setup for 6800 style interface with the onboard controller (SSD1963). This winds up requiring 22 GPIO pins. I have been an engineer in the LCD industry for 6 years now, so I know my way around most types of LCDs and configurations…but I am a relative newbie to the BBB.

I have disabled the HDMI port in the uenv.txt file and have confirmed it to be disabled. The 6 control lines are connected to P8 pins 9-14, and the 16 data pins are connected to P8 pins 29-44. 3.3V power is taken from P9 and GND is taken from P8. When I physically connect the display to these pins, the board does not boot. I get an LED to come up but then it seems to pause and never boot. The display requires a max current of 220mA which I know is close to the limit for the 3.3V supply, so I left the connections made, but removed the power to the LCD. Same issue. I checked for shorts on the connections…none that I could find. There is NO buffer between the LCD and the uC as the boards have not been spun yet. I am hooking it up using an FPC-to-wire converter cable.

Given my relative noobishness to the BBB hardware, I was hoping someone would have some fundamental oversight I am making here.

Thanks.

2

I suspect that your LCD design is interfering with the boot pins that are co-located with the LCD pins which is changing the boot order.

I suggest that you read the System Reference Manual for more information.

Gerald

3

I am having the same problem. After many testing, I found that the LCD pins 2,3 and 4 are being pulled down by my LCD if it is not powered. I confirmed by removing pins 2,3 and 4. The BBB booted while LCD is attached and unpowered. When I connect the LCD pin 2 (sysboot 2) It won’t boot unless there is an SD card. This the same as the boot switch pulling the sysboot 2 to ground. So what I am thinking now is to have a mechanism that will disconnect this when the LCD is not powered. I don’t know if adding level shifters or buffers with the same power rails connected to the LCD supply will work. What Else can I do?