Hi Johnny...I think you're confusing the KDT (AKA the Otis Brick) with the old Tandy 100, 102 computers. I don't believe the KDT had a serial port wheras the old tandy's did. The KDT talked via a LAN network wirelessly. More info below..

http://www.networkcomputing.com/815/815centerfoldtext.html

Of course that was back in the day.

The old Tandy's were pretty cool for their time. You really didn't have an operating system on the old Tandy's except for GW basic. You didn't have a hard drive but could save your programs to casette, or to EPROM which you could install back of the Tandy on the empty chip slot. It also had an ultra-cool 300 baud modem, and you could get an acoustic coupler that would fit over the old phone hand sets, and let you communicate to places like CompuServe.

I've got several of the old Tandy's, including some in the plastic case, with cassette and acoustic coupler.