The TNC2S is a Terminal Node Controller for Packet Radio, just like its faster brother TNC2H. The main difference is that the TNC2S operates links with 1200 bit per second. Way back in the early 1990s I soldered this device myself. It was one of my first major self-soldering projects, and astonishingly enough, it worked fine.
Today it serves as a APRS digi controller and is in active use. See: http://aprs.fi/?call=dl8rds-10&mt=m&z=10&timerange=3600