The digital outputs of the PDQ Board, QCard Controller, and other Wildcards are not open-collector. In their high state, they are open circuits, and in their low state they pull the output pin to ground, sinking as much current as needed, up to a limit. Essentially, they act as simple switches to ground. Open-collector or open-drain outputs do not source current, they can only sink current.
When driving external devices, it is sometimes necessary to use open-collector or open-drain outputs.
