special (possible not usable) pins on ESP32 S2 WROOM:
+---------+----------+----+ | Name | function | note | +=====+==========+======+ | IO 0 | RTCGPIO0, GPIO0 | boot option | | IO 2 | ?no output to high? | | | IO 5 | ?no input? | | | IO 15 | RTCGPIO15, GPIO15, U0RTS, ADC2CH4, XTAL32KP | optional external 32.768KHz crystal | | IO 16 | RTCGPIO16, GPIO16, U0CTS, ADC2CH5, XTAL32KN | optional external 32.768KHz crystal | | IO 18 | RTCGPIO18, GPIO18, U1RXD, ADC2CH7, DAC2, CLKOUT3 | pullup with VDD, my affect chip's entry into download boot mode | | IO 19 | RTCGPIO19, GPIO19, U1RTS, ADC2CH8, CLKOUT2, USBD- | USB OTG | | IO 20 | RTCGPIO20, GPIO20, U1CTS, ADC2CH9, CLKOUT1, USB_D+ | USB OTG | | IO 26 | SPICS1, GPIO26 | internal PSRAM connection, not usable | | IO 45 | GPIO45 | strapping pin, see datasheet | | IO 46 | GPIO46 | Input only, strapping pin, see datasheet | +---------+----------+----+