Anyway, to answer your questions, for a chip interfaced to a data bus, all output pins has to be made open-collector. An open collector output can only sink but not source current. Think of it having the capability of pulling the line to ground, but otherwise floats the line. You can probably figure out the reason when you have multiple chips sharing the same bus.
Most chips meant for bus interfacing already have this capability. If the chip you want to use doesnt, then there are several alternatives. Using tri-state buffers is one of them, though it's probably cheaper to use open-collector buffers.