connect two outputs together

[uzer123]

i use esp32 that uses GPIO pin 14 to output PWM at boot...
but i have to use the same pin as input for interrupts that are active low from ds3231 rtc..

I have connected them and looks to work fine..
but i have the question..what really happens when you connect 2 outputs together? i mean maybe here i dont have a problem that GPIO14 outputs only at boot..but what happens when two outputs are connected?

[JohnLincoln]

If  one output goes high and the other goes low, then they both are likely to sustain damage.

Can you guarantee that they will both always be in the same state?

[uzer123]

what i guarantee is that the one will be HIGH momentary (only at boot), the other will be HIGH unless there is an interrupt..

--PS: i managed to pick other pin...but i still have the question...

if both are 3.3V i am ok because its zero voltage difference..
but then i have 3.3V at the one pin and 0V at the other i have 3.3V difference without resistor in between?

[gutbag]

A low value resistor in series should protect both outputs and still work for input. You'll have to work out the resistor value from the maximum output currents on both sides.

[Grumpy_Mike]

Connecting two outputs together is very bad practice. Simply don't do it.

Why can't you use separate pins?

[david_2018]

Check the data sheet for the DS3231, the interrupt output is open drain, but there is generally a pull-up resistor installed on most clock boards.  An inline resistor would solve the situation where the interrupt occurs while the arduino is outputting a HIGH.

[uzer123]

Connecting two outputs together is very bad practice. Simply don't do it.

Why can't you use separate pins?

its esp32 cam and  i have used most of the pins..
but finally i changed one of the other pins and used  a "good one" for the interrupt..(exchanged for the one of the two i2c pins)

Check the data sheet for the DS3231, the interrupt output is open drain, but there is generally a pull-up resistor installed on most clock boards.  An inline resistor would solve the situation where the interrupt occurs while the arduino is outputting a HIGH.

I have checked with oscilloscope, if there is no alarm, its HIGH.. so i guess it has a pull up resistor in my board..