[GreenKeys] Teletype Data Terminal Accessory

[Jim Haynes]

On Sat, 5 Aug 2023, John Nagle wrote:

> Oh, cute. The electronic successor to the Stunt Box.
>
> That thing talks what Teletype seems to have called "8A1" protocol,
> which is ANSI 3.28.
>
As I recall the 8A1 system was developed entirely in-house at Teletype
and was a system for multistation lines.  The controller polled stations
for traffic to be sent and then allowed them to send if they had any.
It was entirely wired logic.

There was a clever feature to protect against torn feed holes in the
paper tapes to be sent.  A problem with paper tape systems is that if
the tape gets snagged during transmission the tape reader will rip out
the feed holes and keep sending the same character over and over.
The controller copied everything sent on the line.  Characters went into
a shift register.  If two adjacent characters in the shift register were
the same, and remained the same for some period of time it could be safely
assumed that something was wrong.  The controller would send a break
to stop the out station from sending.

The system was originally designed using the Model 35 stunt box to do the
work at the out stations, very much the same as had been done with Model 
28 equipment for years.  As I mentioned recently, business office 
customers complained about the machines sounding busy when they were not
printing anything, so the electronic stunt box was developed to eliminate
that complaint.  Also it would allow Model 33 machines to be used instead
of 35s.

It sounds like various computer companies had machines that could emulate
the 8A1 station controller and do other useful things besides.  I recall
the G.E. Datanet 30 had software for the purpose.  AT&T was prohibited
from using computers by an interpretation of the 1956 antitrust consent
decree.  Although later Bell Labs was developing what was called #1 ESS 
ADF, using the computer of the #1 ESS telephone switching system and
programmed to do the kinds of things that data switching systems did.
The official story is that work on #1 ESS ADF ceased when TWX was
sold to Western Union, as AT&T had no further use for it.  Of course
the consent decree, which aimed to put a fence between data communication
and data processing, became increasingly unwieldy.  There was the FCC
effort to define the boundary, which was pretty much abandoned as a 
failure.

Concerning G.E., you might enjoy this little item from St. Patrick's
Almanack

"In ten years half the computers we are manufacturing will be talking
to each other by telphone"
    Bob Johnson, G.E. Computer Department, 1962
"On what basis do you make such a preposterous statement?"
    Ralph Cordiner, Chairman of the Board of G.E. [who had decreed
    earlier that G.E. would not get into the computer business]