- Thu Sep 17, 2020 10:42 am
I have measured the pullups during the boot phase by using a 100K pull down which is insufficient to lower the logic level below 1. At boot time it gives a pin level of 2.56V relative to a 3.25V supply which corresponds to a internal pull up resistance of 27K. I have found this value to be fairly consistent across different batches of units.
GPIO02 does indeed have a burst of a clock output around 36KHz but this starts after the boot mode has been determined and has no effect on it. It occurs even with an external pullup.
A static measurement of the input pullup can also be made by setting the GPIO to INPUT_PULLUP and this gives similar results.
If no wire is attached to these pins then it would take a huge amount of noise to disturb the boot mode with this impedance.
Now if one is attaching external equipment then its characteristics need to be taken into account, but the question was about floating pins.