Use this forum to chat about hardware specific topics for the ESP8266 (peripherals, memory, clocks, JTAG, programming)

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By ficeto
#9767 GPIO 16 is the only one with pull-down as far as documentation goes for PINs
All GPIOs from 0 to 15 have only pull-ups.
What you are trying to do will not work even if pull-down is available if I understood what you want. You have access to the register way after the boot mode is triggered, so your only option is to use a resistor.
Really sucky they used GPIO15 for that purpose because it kinda breaks the SPI Slave since GPIO15 is the SS pin.