Open Drain Output to Microcontroller?
It seems you want to sense the state of a open drain output with a microcontroller.

Open drain outputs only actively drive low.  For the logic high state, they go to high impedance instead of actively driving high.  Something else needs to make the line go high when the open drain output is in the high impedance state.  Otherwise, the line will stay low once it is driven low.

The usual solution is to connect a resistor between the line and the positive supply.  That's such a common thing that it has its own name of "pullup resistor".  10 k&Omega; is a good value for most ordinary cases.  I go into detail about the value to use for a pullup resistor HERE.

Check the datasheet of your microcontroller.  Many micros have internal passive pullups that can be enabled on some of their pins.  If you are using such a pin, then you don't need any external part at all.  Just enable the internal pullup in the micro.