A good place for information on rotor controllers/interfaces is the satellite tracking programs listed on the www.amsat.org
website. Look in the documentation for each controller
The NOVA program has information on a very simple solution that uses a commercial multipurpose USB interface box, you then build a small board with the TTL components which can connect directly to Icom control port. Once you look at the circuit it is simple to modify it for other brands of rotors with or without control ports. **Note, the Labjack U12 has both USB & Serial DB25 interfaces.
Click image for larger version. Name: ljpb.gif Views: 0 Size: 56.6 KB ID: 91160
Click image for larger version.
Name: lj_piggyback.JPG Views: 3 Size: 68.5 KB ID: 91159
The Piggyback could easily be made up on perfboard. The IC chip costs about 65 Cents. I have one of these!