15 Aug
2014
15 Aug
'14
9:47 p.m.
From: Brian Zick <brian(a)zickzickzick.com>
Would it still be possible today for someone like me
to go out, and
find an old teletype terminal (an old ASR or DECwriter or something),
set up a phone line and modem and get a roll of paper, and then
actually use it to connect to other computers?
Well, although I used ASR33's for two years (attached to an 11/20 running
RSTS :-), it was a long time ago (I was 15/16 :-), and they aren't something
I _really_ know about, but ... Here are some issues you need to watch out for:
First, I think most Teletypes used what is called '20mA current loop' serial
line electrical interface standard (although some of the later ones could use
'EIA' - the now-usual, although fast disappearing, serial line electrical
interface standard). They are logically (i.e. at the framing level) the same,
but the voltages/etc are different.
The only Teletype I see listed (in a _very_ quick search, don't take this for
gospel) that used EIA is the Model 37. So if you get a Teletype Model 33 or
35, and want to plug it into a computer, either the computer is going to have
to have an _old_ serial line interface (e.g. DL-11A/C, on a PDP-11), or you're
going to have to locate a 20mA/EIA converter (I've never seen such a thing,
but I expect they existed).
And if you want to plug it into a modem... all modems I ever heard of are EIA
(at least, the ones you could plug terminals into - e.g. in most PC modem
cards, the serial interface is entirely internal to the card).
Second, most of those Teletypes were 110 baud (mechanical hardware
limitation).
So that means that first, if you plug into a computer, your serial interface
has to be able to go that slow. Second, if you're dialing up, you need to find
a dial-up port that supports 110 baud. (I would be seriously amazed if any are
left...)
Of course, if you go with a DecWriter, some of these issues go away, but be
careful: some older DecWriters were 20mA too, and the speeds were almost as
slow on many (probably 300 baud, but I don't know much about DecWriters).
Sorry to be so much cold water, but...
As for finding one... I suggest eBay. There's a broken ASR33 there at the
moment - if you're _really_ serious, might be worth buying as a parts
source. But if you wait, I'm pretty sure one will eventually float by...
Noel
15 Aug
15 Aug
9:53 p.m.
New subject: Teletype
On Aug 15, 2014, at 3:47 PM, Noel Chiappa <jnc(a)mercury.lcs.mit.edu> wrote:
Of course, if you go with a DecWriter, some of these
issues go away, but be
careful: some older DecWriters were 20mA too, and the speeds were almost as
slow on many (probably 300 baud, but I don't know much about DecWriters).
Sorry to be so much cold water, but...
DECwriters were quite slow. The ones I used (which I think were actually DECwriter II)
did 300, 150 and 110 baud (there was a push button to select. They did indeed
have EIA and 20mA versions, but the difference was a single board inside which
was easy to swap out for the other part. Even when it wasn’t easy, I worked
with a group of people that used one as their line printer with a fairly simple
transistor translator circuit (since that was a lot cheaper than the correct
board). But no matter how you slice it, 300 baud is slow. We likely wasted
way more time waiting for printouts than we saved for the “free” DECwriter
that we got…
Warner
10:01 p.m.
New subject: Teletype
Noel Chiappa scripsit:
First, I think most Teletypes used what is called
'20mA current loop' serial
line electrical interface standard (although some of the later ones could use
'EIA' - the now-usual, although fast disappearing, serial line electrical
interface standard). They are logically (i.e. at the framing level) the same,
but the voltages/etc are different.
Current loop to EIA RS-232 (which is the relevant standard) converters
are readily available, saith Google. There are also RS-232 to USB
converters for the other end.
So that means that first, if you plug into a computer,
your serial interface
has to be able to go that slow. Second, if you're dialing up, you need to find
a dial-up port that supports 110 baud. (I would be seriously amazed if any are
left...)
I dialed up The World's local dialup line for my area, and heard a large
variety of tones including Bell 103-compatible FSK, which is 300 baud.
I suspect that anything that can do Bell 103 can fall back to Bell 101,
which was 110 baud. I admit to never trying it.
Note that it's 110 baud because there are a start bit and two stop bits,
so it's really 10 cps. 300 baud has only one of each, hence 30 cps.
Of course, if you go with a DecWriter, some of these
issues go away, but be
careful: some older DecWriters were 20mA too, and the speeds were almost as
slow on many (probably 300 baud, but I don't know much about DecWriters).
The LA36, the only one I ever used personally, was 30 cps, ergo 300 baud.
(Note that it buffered and could print faster to catch up after a long
carriage return.) There was also an LA120 at 120cps.
--
John Cowan http://www.ccil.org/~cowan cowan(a)ccil.org
"Not to know The Smiths is not to know K.X.U." --K.X.U.
16 Aug
16 Aug
1:56 a.m.
New subject: Teletype
On Aug 15, 2014, at 3:01 PM, John Cowan <cowan(a)mercury.ccil.org> wrote:
There was also an LA120 at 120cps.
Ah yes! The APL terminal of choice at the U of Alberta for the APL hacks. Late nights in
the terminal rooms in GSB ... (and the mystery room on the 4th floor of CAB).
--lyndon
2:12 a.m.
New subject: Teletype
On Aug 15, 2014, at 6:56 PM, Lyndon Nerenberg <lyndon(a)orthanc.ca> wrote:
Ah yes! The APL terminal of choice at the U of
Alberta for the APL hacks. Late nights in the terminal rooms in GSB ... (and the mystery
room on the 4th floor of CAB).
Actually, the hardcopy terminal room on the 3rd floor of GSB was filled with dog slow
DECwriters, now that I think about it. Next door was a room full of CRT something or
others, all wired to the Amdahl running MTS, so curses was just another curse. There was
also one terminal room full of Courier 3270 clones (wonderful terminals, with
indestructible keyboards) also wired to the MTS Amdahl/470.
Funny how the MTS line editor resembled ed(1) so much :-)
--lyndon
9:28 p.m.
New subject: Teletype
U of M had the Teletype room which had teletypes (ASR 33's) with integral dataphones.
These got replaced with the LA36 decwriters most of which had APL character sets as
well. Upstairs was the Hazeltine room full of a half dozen Hazeltines that used ~ as the
graphic escape (causing the HAZEL stty mode...leave poor tilde alone!) and one Tektronics
storage scope monster.
My first C program was on one of JHU's teletypes complete with \( and \) for it being
upper case only lacked the { } characters.
3551
days inactive
3552
days old
5 comments
5 participants
participants (5)
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jnc＠mercury.lcs.mit.edu -
John Cowan -
Lyndon Nerenberg -
Ronald Natalie -
Warner Losh