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IBM PC to teltype?

RickNel

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Apr 24, 2009
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Canberra, Australia
Also, be aware that teletypes come in two encoding flavors, the so-called "7 level" or the ASCII-speaking one (e.g. model 33) and the "5 level" (e.g. model 35) which uses its own code.

I used an adapter from a S100 CP/M machine to a 5-level international telex machine - the code was called BAUDOT.
The adapter converted RS232 signal from a serial printer port to current loop at standard telephone line voltage. Some driver code converted ASCII text to BAUDOT output. IIRC no handshaking was used. ASCII bit 6 triggered the register shift, I think. I still have the 8-bit 8080 Assembler source for that driver, if OP or anyone else wants to run a 5-level BAUDOT telex machine from a RS232 port. Standard baud rate was 50bps - a bit less than 5 chars per second. The hardware adapter was fairly simple as I recall, but what I have left of it has been robbed of some components over the years and I don't have a schematic.

My setup was output-only. Presumably a reverse adapter for input would be equally simple.

Rick
 

Chuck(G)

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Yes, I know that people call the code "Baudot", but strictly speaking, that's not what it is--the "modern" 5-level code is ITA2 and is a modification of a code called "Murray Code" which is a modification of Baudot's scheme by Donald Murray. In short, Baudot's code was made for a 5-key keyboard and one operated it by depressing various combinations of keys. The characters in Baudot's code are quite different from ITA2--and you would not recognize many of them.

Yet another misunderstanding of the word "Baudot", I suppose. I wanted to avoid the whole business of having to explain my use of "5 level", but I guess that I ended up doing it anyway.

And yes, back in the early days of hobby computers, one could, with a minor amount of software and some lookup tables, convert 7-level ASCII (other variants of ASCII do exist, but that's another story) to an ITA-2 representation. Note that ITA-2 does not have many special characters, nor does it have lowercase, so there are some compromises.

A similar setup was used when driving IBM I/O Selectric terminals, such as the 2741. Normal "golf ball" character coding uses a "rotate and tilt" code, usually called "correspondence code", which bears no resemblance to any computer code. So you could either use software or purchase a box to handle the code conversion. There were somewhat harder-to-find type balls that were used on S/360 operator's console Selectrics that had characters ordered to correspond roughly to EBCDIC. A practical joke that was sometimes played on operators and secretaries (no "administrative assistants" back in those days!) was to swap the typeball types. The units would work fine with either--but what came out was pure gibberish.

I've said too much already, sorry.
 

josephdaniel

Experienced Member
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Jul 3, 2012
Messages
317
Location
Florence, Texas, United States
Thanks, I think that I now know the difference between the level 5 and 7 codes.
One more question on a modern computer (windows XP) would it be possible to control a teletype with its rs-232c port with a terminal emulator or something?
 

billdeg

Technician
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Nov 18, 2003
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Landenberg, PA USA
If the teletype has been converted to RS232 then it's the paper/printer equivalent of a glass terminal. You could download text files to the terminal using TeraTerm or Kermit.
 

MikeS

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Dec 23, 2005
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Toronto ON Canada
That is amazing! I just ordered a nixie tube clock kit from pv electronics that I have been saving for for a really long time but this is next on my wishlist!
Wow, those things are getting expensive; I sure regret throwing out a case of 24 pcs. 6" tall Burroughs Nixies...

Re the Teletype: don't forget the mechanical challenges. They take a fair bit of maintenance and some special tools; lots of little levers and springs in there, sticky oil and grease, dirty contacts, none of it easy to get at...
 

josephdaniel

Experienced Member
Joined
Jul 3, 2012
Messages
317
Location
Florence, Texas, United States
I think I might be ok with the machine being gummed up All of my selectrics were and I was able to get those working good with allot of digging for Manuel's
About the Nixie tubes I think allot of sellers are just milking the price I got 6 in-14 tubes for 40.00 from ukrane and I think I payed too much but these were expensive when new.
 
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