I am using the STLINK from a Nucleo board in order to flash and debug a STM32F7 MCU on a custom board.
Everything works fine except when STLINK is connected to my custom board AND unpowered. Indeed, in this case the MCU on my custom board doesn't seem to start.
After some investigation, I realise that it is the NRST pin (CMOS technology) from the STLINK which is shorted to GND when unpowered, shorting to GND NRST on my custom board.
A simple workaround is to disconnect the NRST pin from STLINK when it is unpowered but I would like to know if there is a way prevent NRST from being shorted to GND without having to disconnect this cable.
I tried a 10K pull-up resistor to VDD of my custom board but of course it doesn't change anything as it seems to be a real short to GND and not through a pull-down resistor.
Does anybody have knowledge of the exact architecture of the CMOS driver of NRST pin ? The piece of information provided by datasheet (p.67) is not really helpful as there are no exact characteristics of the CMOS themselves.