ESP32 Forum

Hi all,

I want to ask what happen if I use a 1.8v (1.7-2.0v) SPI memory with a pull-down on MTDI/GPIO12 strapping pin. From datasheet I've found that 3.3v mode is used with a pull-down, but if I've a 1.8v flash, 3.3v mode starts before or after check user code? Or is memory fried before start user code?

Hi Singe12,

If you pull MTDI high on reset then the internal VDD_SDIO regulator will start up at 1.8V not 3.3V. The value of the pin is read before this power domain's regulator is enabled, and before any user code can be executed (as the user code is loaded from flash).

If you pull the pin down (or leave it floating) then the regulator will start up at 3.3V and may damange your 1.8V flash if it's not specced for this voltage.

For more details, see ESP32 Technical Reference Manual section 4.8.1 "VDD_SDIO Power Domain".