Tracy writes:

> I needed to know if I need an RTTY converter or can it be done
> programattically.

It can be done quite easily. It's only a SMOP (small matter of programming) 
and a SMOHD (small matter of hardware design). Baudot is 5-bit code (the 
sixth track on a baudot paper tape is merely the clock track). The most 
important aspect of such a project is that you will need to obtain either a 
mechanical or optical reader that outputs its data at RS-232 levels before it 
can be inputted into a standard computer port.

As for converting the actual data, that requires nothing more than a 
translation table, but with special emphasis on the LETTERS and FIGURES 
characters.

Every bit pattern in baudot, with just a few exceptions, serves double duty, 
much like the SI and SO (shift in, shift out) control characters do in HP 
terminals that switch between various character sets (alphabetic, line 
drawing, math/symbol, etc.).

While HP terminals tend to stay in their proper character set, RTTY devices 
running baudot had a terrible tendency to flip between LETTERS and FIGURES 
due to the misreception of characters during a radio noise storm. A thousand 
years ago (or at least during the previous millennium) when I was out in the 
South Pacific tracking satellites, all of our communications were by RTTY:

   http://aics-research.com/history1.html

...and quite often a long communication would arrive completely scrambled. 
Only because every incoming message was recorded on paper tape could we 
take the tape and run it back through the teletype's tape reader, in local 
mode, and artificially force the machine into the proper LETTERS or FIGURES 
mode and deduce what had been sent to us.

Here's a Wikipedia article outlining the translation table that you'll need if you 
wire the baudot output to the bottom five bits of an ASCII port (but there's no 
reason that you have to do that. Indeed, wiring the input so that the output 
is offset upwards by two bits and forcing the bottom two bits to always be 
zero would probably be the better and easier way to go:

   http://en.wikipedia.org/wiki/Baudot_code

Wirt Atmar

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