What does "open drain" mean?

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Discover the functions of open drain and open collector circuits

There is a popular post here on the DigiKey TechForum that explores the “what” aspects of an open drain configuration. The post presents the open-drain concept as a digital circuit that requires an external pull-up resistor. That is a good answer, but we should expand our knowledge by asking “why” an open drain circuit is desirable. Before we start, let’s make a running list of logic devices that feature either the open drain or open collector connections: 74 series logic:7401, 7403, 7405, (…