Using GPIO2_6 to GPIO2_15 as inputs

I know, I should have asked this question 6 months ago but I had very little idea about I/O pins then. Only knew that those pins were used elsewhere and that up to 65 I/O were, supposedly, available.

So I have managed to disable HDMI and now I can access 48 I/O pins which I need, however the above are messing up boot when pulled high, which is what the cape does.

After Googling until my eyes popped out I thought I’d ask here if there is a way of disabling the scanning of those pins at boot up and, somehow, allow booting from EMMC only.

Is there some EEPROM or “fuse” settings for that?

I guess I could use internal pull ups of those 10 pins after booting up but it would be much nicer if I used external pull ups like other 38 pins.

Another option would be to use tristate buffers which would enable I/O access after boot up but that would require an additional I/O pin which may not be easily accessible. Anyway it would mean a PCB revision which is not really what I want to do right now.

So, unless there is a magic way of disabling I/O pins look up, the only other option seems to be internal pull ups.

Unfortunately nodejs doesn’t seem to like INPUT_PULLUP for some reason so I can’t test it.

No. The boot pins are used by the hardware when it comes out of reset
to determine the desired boot mode. If you wish to drive these pins,
you need to insure you do so only after the system reset line goes high.

This is all covered in the BBB SRM.

Thanks Charles, I was afraid of that. I’m learning a lot, real fast.

SRM?? Something new, I guess it’s the equivalent of “Read The Fabulous Manual”? :slight_smile:

So it’s back to using the internal pull ups for those pins, not too bad I guess. If I need to make another board in the future I can use a couple of 74HC365 tristate buffers to isolate those pins at reset.

SRM = System Reference Manual

You can find it alongside the hardware design files:

Sections 8.1.1 and 8.3 cover using the LCD/boot pins.

Got the current SRM, my PDF was January 2013!

I guess not Mr Coley’s finger nails on the 1st page? :slight_smile:

So does the BBB have 65K ways of booting up? It surely seems to be an overkill using 16 pins, but what do I know. :slight_smile: