A6 boot pin pull-up/down values


On the bone rev A6A schematic, on page 1 in the revision listing, item 8
within the A6 rev says, "Change pullups on the boot pins to 42.2K per
AM335x design team."

But the pull-ups are still 100 k-ohm. The pull-downs, however, have
changed to be 42.2 k-ohm. We've pulled off R80 and R81 and they measure
100 k-ohm, we've also pulled R103 and it measured 42 k-ohm. This
contradicts the note on page 1 but confirms schematic page 6.

Should the pull-downs be 42 k-ohm and the pull-ups be 100 k-ohm, or vice
versa? Or should all pulls be 42 k-ohm for boot pins?

Related, I've been looking through the AM335x data sheet and TRM and I'm
having trouble finding the recommendation on boot pin pull value. Any
pointers to a page or section number?


I would make them all 100K. We plan to switch back to 100K on the next revision. he idea was that the pull downs would be switched to 42.K, and that was what was done. The text is incorrect in the schematic. Follow the BOM, that is what is being built.


OK, thanks.

Can you expand on why the change was made to 42 k-ohm and why you're
inclined to switch back to 100 k-ohm? Were there issues with the boot
mode with all pulls at 100 k-ohm?


Well, some chip heads here at TI felt that the 100K could be too high and that 42K would be better to insure proper detection of the boot pins on power up. However, we have had issues overdriving them from capes when we want to change the boot order. I never saw any issues when it was at 100K. So, I plan to move it back to 100K.