Open drain on Infineon board

On an Infineon board (C167CS) I configure an output pin to be in open-drain mode and then I see with the oscilloscope that the output stays at 0V, whereas on a different pin, again in open drain, a LED attached to it switches on. Why don't I see any voltage change with the oscilloscope? Shouldn't a pullup resistor pull the output pin to some voltage when I change its value to logic '1' as in the case of the LED?

it required pull up registers

An open drain output is (as the word says) a mosfet with the drain unconnected,
You have to connect a resistor/load to the drain externally.
When the mosfet is off then no current flows through the mosfet (and the load) so the drain gets the voltage through the load ,the source-drain resistance is high so the resistance/load works as a pullup/pulldown (depending on the output type),
When the mosfet is on then the current flows through the mosfet and the resistor/load and you get the source voltage to the drain , low source-drain resistance and voltage drop across the load.

Think of it as floating drain when the mosfet is off and drain connected to the source when on, you have to connect a pullup/down to provide a voltage while the drain is floating or you will not measure any voltage.

Check this
**broken link removed**

Alex