What is voltage threshold for the boot pins?

[Dat Tran]

Hi, 

On STM32MP1, what is voltage threshold for boot pins to be detected as 0 and 1 in digital?

Will 0.61V be detected as 0?

I research seem under 1.23V will be 0 and start from 1.88 or higher will be detected as 1 (if VDD = 3.3) but I am not sure this is applied for all STM32 or not.

Many thanks.

[TDK · Accepted solution]

Thresholds are given in the datasheet. Anything less than 0.3*VDD is guaranteed to be read as logic low.

0.61V when VDD=3.3V will always be logic low.

[Tesla DeLorean]

Also depends on how quickly/slowly the VDD voltage is rising, and the point at which the MCU internally is viable.

Figure close to 1.2V for viability.

You pull BOOT0 low so it's tending to zero out of the gate...

[PatrickF]

Hi @Dat Tran ,

on STM32MP1 products, BOOT pins are sample by BootROM (i.e. some time after NRST is becoming high) with standard GPIO input levels (VIL/VIH listed in datasheet as mention by @TDK ). Note that BOOT pins have internal pull-down by default (RPD listed in datasheet).

It is strongly recommended to have clean and stable logic levels on BOOT pins when NRST is high as this could lead to very weird issue when you will product quantities due to variations on process/temperature/voltages.
i.e. avoid wired logic using diodes or any fancy glue on BOOT pins.

Regards.

[Dat Tran]

Thank all of you for the answer.