Mapping the Outputs of a 1960s Teletype Machine - How Hard Can it Be? -- Episode 546

The application of what we learned aboutthe teletypes innenr workings is no up!
/challenges-projects/element14-presents/project-videos/w/documents/27606/episode-549-using-a-teletype-machine-as-a-usb-printer-with-arduino

check it out and let me know what you think on how we should go forth.

yes, there are soem special characters like the iron cross that could be repurposed, but still a few are missing.
it may be possible to do a translation layer where for example this unused symbol shifts to a third set that depicts the ,issing symbols, but yeah its a rather crude hack....and encoding on paper tape would be even more tricky.

Yes, but there has to be slightly more to it than that as there doesn't appear to be enough figures codes to contain all the symbols required for special characters in BASIC.

Baudot is 5 bits so 32 code patterns in total.

In ITA2 encoding, NULL , CR, LF, Space, Shift-to-Figures and Shift-to-Letters are all reserved codes, leaving 26 codes in letters mode and 26 codes in figures mode.

In Shift-to-Letters mode, all 26 codes are taken up by the alphabet.

In Shift-to-Figures mode, 10 codes are allocated to numbers 0-9, leaving you with only 16 codes left for any symbols (one of which usually is taken by BEL, so 15).

BASIC needs at least 21(?) symbols in addition to the space character  = + - * / ) ( , . ' " ; : ! ? & < > # $ % 

The only way to get that would appear to be switching between international and US character set variations mid transmission, or alternatively using escape character sequences. If there is a dedicated key on the keyboard for each of those symbols then the mechanics must be doing something interesting to fit it into the 5-bits in a uniquely identifiable way ?

It looks like the Russian variation used the NULL code as a third shift-to-Cyrillic option.

there is a dedicated key to send the signal for each character set( so one key for Letters, and one for symbolds, nott like a shift key) that prints the shift code on punchtape and also sets the machine to the specific state to print those characters.
you can by a few little details in the mechanics tell in which state is currentlsy is..but I misjudged that many times during tests.

in the upcoming episode I have achieved a full aplhabet but did not implement the full set yet due to time constraints.

The lack of symbols on the Model 15 US keyboard made programming on the Linux terminal rather tricky. Looks like your S100 may be doing something interesting to transparently change between the optional character sets in order to get the wider range of characters.

Using a 1930's Teletype as a Linux Terminal:
https://www.youtube.com/watch?v=2XLZ4Z8LpEE

to me it looks siemsens took a modular approach early on with the Fernschrieber Series, you could get every model they made in typerwiter only punchtape in and Out as well as all combos and the whole thing integrated into a desk.
for sure none of those were a budget option.

Excellent. That sounds like an enhancement with those later machines. It looks like in the earlier days you had to use a 'reperforator' machine to create a punched tape in real time from a received signal. It also decoded and typed the characters directly onto the punch tape as it was punching it which is pretty handy.

Teletype Model 14 Reperforator:
https://youtu.be/Jhn3AYHwSqg?list=PL-_93BVApb5-9eQLTCk9xx16RAGEYHH1q&t=34  

The earlier machine configurations appeared to need three separate units to cover all your bases. The main teletype itself for receiving to paper and for creating punched tape from keyboard. The transmitter/distributor for transmitting from punched tape. And the reperforator for receiving to punched tape. (Oh and don't forget the thyratron mercury rectifier tube PSU for powering it all.)

the current pla is to turn this into the IO system for a z80 based Computer. not quite alinux term but it can send and receive al lthe symbols used in BASIC.

I can confirm you can make direct copies of punchtape with the machine (it simulataniously prints it on the sheet of paper during the process)
its also possible to put it in an endless loop by feeding the the ape back in the reader/ gluing it into a loop.

Now that Iḿ deeper into the project I can confirm it uses a current loop, but it was shorted to turn it into a local unit (likely straight at the factory)
I used the mechanical visuakl indicators to identify the Characteristics of the encoding like MSB/LSB and start/stopbits, but it was very confusing for me, since its not visually consistent over the whole machine so I was often second guessing my findings.