[TUHS] Teletype

[cowan@mercury.ccil.org (John Cowan)]

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 at ccil.org
        "Not to know The Smiths is not to know K.X.U."  --K.X.U.