[GreenKeys] ASCII <-> Baudot algorithm

[Whitebear1122]

If I may add my 2 cents as a new member of this group.  All the Model 28's that I used in the US Navy in the 70's had unshift on space feature.  As a long operator of Navy Fleet Teletype Broadcast, I can understand the rationale for it.  Bit errors would miss the LTRS function and result in a stuck  line of useless FIGS characters until the typical CR CR LTRS function at the end of a line shifted back to LTRS.  

73, Scott WA9WFA


On Aug 1, 2015, at 9:55 PM, "tony.podrasky" <tony.podrasky at gmail.com> wrote:

> Hello dr;
> 
> Well - it gets even a bit worse than that:
> 
> Some Teletype Machines have a feature called "unshift on space"
> and some have "stayshift on space".
> 
> "Unshift on space" will take the machine out of the FIGS when you
> receive a SPACE character and downshift it into LTRS.
> 
> "Stayshift on space" will leave it in FIGS when you
> receive a SPACE character.
> 
> The difference: you type   QWE 123 123 QWE
> 
> If you don't add the appropriate FIGS or LTRS key after the SPACE
> here's what you're going to see:
> 
> UNSHIFT: QWE 123 QWE QWE
> 
> STAYSHIFT: QWE 123 123 123
> 
> Both have a reason for existence:
> 
> STAYSHIFT was used for PIREPS (Pilot Reports) and was lines of
> groups made of 5 numbers with about 10 groups per line.
> 
> UNSHIFT was used especially for RTTY because when there was static
> or fading, the machine might get stuck in FIGS and you'd have to
> translate the numerical stuff back to text stuff.
> 
> SO: when you write your program, you have to take (that) into
> account - so no matter how the data is coming in or going out,
> the message will appear the same.
> 
> If you were working with C I could give you some pointers, but I
> don't know anything about a C-64 anymore.
> 
> UE,
> K2EAA - TONY
> NNNN
> ZCZC
> 
> 
> On 08/01/2015 05:19 PM, drlegendre . wrote:
>> 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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