You can use the same API for 485 and 232. However, the cables used are different (even though the connectors may be the same). You can read about 485 communication issues (transceiver (also called "wire") modes, device manager settings, and full/half duplex wiring) in the serial manuals available through the "Support" link in this website. A lot of the material is specific to NI cards though; I'm assuming that's what you probably have.
