STM32F405 GPIO pin

[cjaya.2]

As shown above picture, I got my STM32F405 configured as open drain to drive the led that is connected.Also, the same pin connected to via hex inverted (74HCS04D) to invert it and connected to OR gate. But when the GPIO pin in reset (low) state voltage showing as (2.934V) and set state (high) voltage showing as 3.24V. its not driving down to able for hex inverter to output as 1 when the GPIO pin in reset (low) state. Any help on this. Thank you     

[waclawek.jan]

When the output transistor in mcu is on, current flows freely through diode through transistor to ground, heavily overloading the transistor.

Use an appropriately dimensioned resistor (with regards to output current supported by the mcu's GPIO pin) instead of diode.

JW

[cjaya.2]

Thank you for the reply. Is that the reason I am getting 2.934V at the hex inverter input even though it is low (reset) state. So I should use current limiting resistor.

[Tesla DeLorean]

Cross posted here  https://forum.allaboutcircuits.com/threads/stm32f405-gpio.197717/

Check the specs on 74HCS04D, would have thought 3.3V would meet VIH threshold directly driven in PP mode without any additional circuitry