I rediscovered a RTTY computer interface FSK modem I had bought long ago at a hamfest and never used.  It is the 1983 model CP-1 by Applied Electronic Applications, inc.  The company is alive and well as AEA Technology of Carlsbad, Calif.   See the nice photo gallery at their web page here . 

In the process of learning a little about RTTY details, I found the articles written by George Henry, Jr. ("Bill"), K9GWT (sk), very helpful, especially ASCII, Baudot and the Radio Amateur available here .

The simulation in the slides below is partly to document the CP-1.   I expected to send the unit to recycling, but now I can't bear the thought of it in a crusher.