Pin state at startup.. Hi-Z?

[Hello1024]

I'm having some trouble keeping a pin in Hi-Z mode through a reset.

Take GPIO4 for example of the ESP32-S3-WROOM-1. Lets wire it with a 10k external pulldown resistor.

While the EN pin is low, the output voltage is 0v as expected.

However, when the EN pin is raised, the external voltage rises to about 0.9 volts, despite the pulldown resistor, before user code starts executing.

Is there code in the boot rom/loader/startup that is perhaps calling gpio_reset() on all pins, which would enable the pullup resistor?

Are there any pins which can stay low or Hi-Z through a powerup and reset?

[Jonathan2892]

Hi,

I have the same issue on GPIO11.
Normally I would go by the Table 6.3 in Chapter 6.12 IO MUX Function List of the technical ref. manual.

If I read that table correct your GPIO4 should be input disabled but does not have any pull-up or -down resistors at start-up.
My GPIO11 is the same, except it is input enabled.

I also noticed, that I have this issue not on all of my boards. Some have this behaviour, some not...would really appreciate some help on this, too.

Best

[Jonathan2892]

Hi,

I did some measurements as you can see in the attached picture. You can see, that GPIO11 is somehow going high directly at startup. I have the same PCB (same batch from manufacturer) without these spikes.

Can anyone explain this? Since we are about to start series production, I need to know what is going on and how to fix it. It happens on 3 of 18 PCBs.

Best