In Volume 1 Issue 6 August 1979 of the '68' Micro Journal I see there is a routine to bit-bang 5-level code to a Teleprinter..... .. I know that's late 70's but in the UK older 5-Level machines were available cheaply as the GPO (General Post Office) moved from older Creed-7's onto Creed 444's for its Telex and Telegram service.
I don't know what happened in the US but many Hams had Model 15 TTY's and I would have thought they were available at a reasonable cost , well certainly as compared to a Model 33. Note there was also a model 32 which is 5-level version of the 33... So yes they were used, but perhaps not as the only input device... Dave Wade G4UGM > -----Original Message----- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Brad > Sent: 16 October 2015 07:20 > To: 'General Discussion: On-Topic and Off-Topic Posts' > <cctalk@classiccmp.org> > Subject: RE: Fair price and ways to find a teletype > > Thanks for this great explanation. So would anyone doing computing back in > the early 70s have used a 5 level machine? > > I saw this one on ebay (or is it two? Not sure what the deal is here) It's > probably sacked: > http://www.ebay.com/itm/Teletype-equipment-1-model-28-writer-1- > reperforater- > 1-50vdc-supply-etc- > /121784463105?hash=item1c5aeb6f01:g:UR8AAOSwnDZUJHWs > > -----Original Message----- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Brent > Hilpert > Sent: Thursday, October 15, 2015 10:07 PM > To: General Discussion: On-Topic and Off-Topic Posts > <cctalk@classiccmp.org> > Subject: Re: Fair price and ways to find a teletype > > On 2015-Oct-15, at 6:25 PM, Brad wrote: > > > > Also separate question to others: I want to stay away from the Baudot > machines, right? (ie. Model 28, etc) > > I'd say it largely depends on what your interests or purposes are. > A brief overview of the technology: > > In the main, there were 3 generations of teletypes: > > Era Common Model Code > Speed Common Interface Mechanism > ====== ============ ========== > ======= =============== ============ > > 1) 1930s-40s: Model 15,19 5-level > ~30-50 bps 60mA current loop Modified Typewriter Cage > > 2) 1950s-60s: Model 28 5-level > <=75 bps 60mA current loop Typebox > > 3) 1960s-70s: Model 33 7/8-level/ASCII 110 > bps 20mA current loop Type Cylinder > > These are the "page printers" that would type across and down sheet paper > fed from a roll. > There are other models, variations on the above. > Not included here are the tape printers, simpler mechanisms that printed in > one dimension on a narrow paper tape, ala stock tickers. > > The mechanism was the overriding distinction between these generations as > speed and code capability followed from the mechanism: > > 1) Modified Typewriter Cage: > Decoding bars select 1-of-30-odd symbol/type arms > arrayed in an arc, to swing and hit the paper, just like a common typewriter. > > 2) Typebox: > An ~ 1" by 2" metal box holds typeface symbol pins in > two 4*8 matrices. > The box is shifted up/down and left/right to bring a > selected > symbol pin between a hammer and the paper. > > 3) Type Cylinder: > A cylinder embossed with the typeface is moved > up/down and rotated CW/CCW to select a symbol. > > The 5-level devices are commonly referred to as Baudot devices but this is > not strictly correct as they generally use the ITA2/USTTY codes (International > Telegraphy Alphabet No.2). > > The speed of Model 28s (at least) was determined by a selected gear-set. > > 5-level machines need code conversion of course. > > They all need current loop interfaces. > > A lot of old computer equipment will do 110 bps as the 33s were so > associated with computers. > > For working form modern equipment, the bit rates for all of them are > potentially awkward. > When working on the 28s, which were geared for 75 bps, I lucked out as I > found the USB-serial interface I was using could do 75 bps > - not entirely surprising as 75 is a factor of 2 down in the common > 9600,1200,300 bps series. How many USB-serial interfaces are capable of this > I have no idea. > Regardless, the baud rates are slow enough that bit-banging from a program > is not difficult, or an adjustable RC oscillator to a UART should do. > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2015.0.6172 / Virus Database: 4447/10805 - Release Date: 10/12/15
