Hi,

I try to bring up a custom pcb with esp32p4 on it. I am facing a strange problem - the GPIO37 which is UART TX pin from the ESP constantly outputs some data, plus instead of togging 3v3 - 0V it sits at roughly 800mV DC (1.2 peak2peak) see below:


When I pull down CHIP_PU (reset), the line recovers to 3v3 but then after I release the pull down it immediately start flooding TX again with this weird voltage level. UART RX(GPIO38) on the other hand sits silent at 3v3 as it should.
The chip should be in download mode because I have GPIO36 at 1 and GPIO35 at 0. Also I haven;t populated SPI flash memory yet.

Have anyone encountered this problem already?

Thanks!

 

Is the pin set to "open drain" mode? If so, you need a pull up resistor. Otherwise the voltage is indeterminate. The ESP32-P4 can do such a configuration I believe, even in UART mode.
Probably no harm in using a 10k pullup anyway, to see if that helps that signal.

 

I have absolutely no clue what the pin configuration is because there is no FW downloaded yet. As I said, I am just bringing this board up so it runs of factory ROM code. Is it possible that just because I haven't populated the external SPI flash memory causes it to act up?