[GreenKeys] ASCII <-> Baudot algorithm

[drlegendre .]

Still slogging away at my C-64 TTY driver project. Only now beginning to
look into the ASCII / Baudot conversion issues, and would certainly
appreciate some input on the matter.

While ASCII has 128 possible values, Baudot is limited to 32 which doesn't
even allow for the full US/Latin alphabet plus the ten numerals - much less
punctuation. So it seems that all the numerals and punctuation are
'shifted' characters, using the LTRS and FIGS scheme.

So when a TTY sends the string "ABC123DEF" it actually sends:

LTRS+"ABC"+FIGS+"123"+LTRS+"DEF"

With each printing character represented in it's 5-bit binary Baudot form.

So to implement a conversion routine, I must not only translate between the
ASCII & Baudot values for the chars, I must also know which set the char is
from (FIGS or LTRS) and send the correct preamble to toggle the char set
prior to the character value?

Do I have this correct? Are there standard routines / algos for this, that
I could study? An example in BASIC would be grand, as that would make it so
much simpler on the C-64.

Thanks in advance for any and all comments, you guys have always been great
for this stuff..
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