Won't boot when using hdmi header pins, even though hdmi is disabled

GoogleGroups
1

Hoping someone can help.

I’m trying to use some of the P8 hdmi header pins as GPIOs.

They work fine if I boot the BBB without them plugged in, and once boot plug them in.
But the BBB won’t boot if they are plugged in when power is applied.
Nothing appears on the console tty.

Thanks in advance.

2

I suspect that you are messing with the boot pins. These pins are read to determine the boot mode. Did you by chance read the System Reference Manual on this topic?

Gerald

3

Are you driving any of the pins with a high or low at power on? Every pin in the LCD_DATA range is used by the bone to select it’s boot mode and are configured on the board to be set at a default value. If you drive those pins with another value you just altered the boot configuration. You need a buffer with output enable that is gated with SYS_RESETn. It must not drive those LCD_DATA pins until SYS_RESETn goes high at which point the boot mode is selected and underway. Unfortunately that means you likely also need an inverter for most any common buffer with an output enable.