[GreenKeys] ASCII <-> Baudot algorithm

[Ralph Mowery]

Back in the mid 1970's  to mid 1980's 73 Magazine had lots of RTTY articals about using a computer and some programs for them.  That magazine is in public domain and they can be found on the internet for free down loading.

When using Baudot you normally want to start off  with a CR CR LF LTRS on each line.  The two CRs is incase one is missed in the radio proprgation.  The LF, LTRS gives the carriage time to get back to the left side when running machine speed.  
 Normally every time you go to the FIGS characters you want to send the FIGS and every time you put in a space between the FIGS, you need to send a FIGS as many machines will unshift on space.  It does not hirt anything to have a few extra FIGS or LTRS sent other than a slight reductionin the speed.

Many machine have the shifted J and S interchanged.  One is the BELL and the other is the ' symble.  Often people send both, especially if sending the RTTY pix.

Best of luck on the project.  I wrote a simple RTTY program for an 8080 processor board years ago , but have no idea where the notes for it is.

  ----- Original Message ----- 
  From: drlegendre . 
  To: Green Keys 
  Sent: Saturday, August 01, 2015 8:19 PM
  Subject: [GreenKeys] ASCII <-> Baudot algorithm


  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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