From mboxrd@z Thu Jan  1 00:00:00 1970
From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
Date: Fri, 15 Aug 2014 17:47:26 -0400 (EDT)
Subject: [TUHS] Teletype
Message-ID: <20140815214726.EA12118C14B@mercury.lcs.mit.edu>

    > From: Brian Zick <brian at 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