TTYs for the deaf

From: Eric Smith <>
Date: Sun Dec 12 14:13:08 2004

Tom Jennings wrote:
> The TTY-for-the-deaf tech is based upon older ITA2 (aka "baudot"
> but it's not -- no teletype-like device EVER used Baudot's code,

John C. Ellingboe wrote:
> Teletype Corp. Models 14, 15, 19 and 26 for a few plus some by other
> companies used Baudot code. Some of those were interfaced to early
> micros for lack of a better/cheap console at the time.

AFAIK, the model 28 and 32 use the same five-level code as the 15 and
19. The model 32 is the five-level version of the better-known model 33.

Tom's point is that contrary to popular belief, the five-level
Teletype code is NOT actually the Baudot code. His web page on the
history of character codes explains this in great detail with

Years ago my friend Jim Philips interfaced a model 28RO to his
semi-homebrew 6502-based TLB computer. He wired up some sort of circuit
to turn off the motor when the line when idle (spacing) for more than
a minute or so. I wrote a driver for the APEX operating system, which
normally used ASCII. The driver performed the necessary code conversion.
The tricky part was what to do about printing characters that had no
five-level equivalent. I decided to use overstrikes (somewhat like APL
in principle). The driver kept track of whether any characters on the
current print line needed overstrikes, and if so, would print one pass,
carriage return, second pass, then another CR and a line feed.

I think that's the oldest piece of code I've written for which I still
have source. I doubt that it's of use to anyone, but there are two
versions of it on my web site:

I'm still hoping to recover my program from the same era to format
eight-inch disks on a 1771-based controller.

Received on Sun Dec 12 2004 - 14:13:08 GMT

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