Answer Posted / a3b2

Because the pull up resistor is external and need not be connected to the chip supply voltage, a lower or higher voltage can be used instead. Open collector circuits are therefore sometimes used to interface different families of devices that have different operating logic voltage levels or to control external circuitry that requires a higher voltage . (e.g., a 12 V relay).
Another advantage is allowing to connect more than one open-collector output to a single line. If all outputs attached to the line are in the high-impedance (i.e., logic 1) state, the pull-up resistor will hold the wire in a high voltage state. If 1 or more of the device outputs are in the ground (i.e., logic 0) state, they will sink current and pull the line voltage near ground.

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