[GreenKeys] ASCII codes

[O. Warren]

Hi list....

I'm a retired Western Union Field Service Technician/"Tech Rep".
I went to W.U. school for all the various "Teletypes", from the Model 15 on,
excluding the Model 40 video/computer terminal..

They told us that the ASCII code system and the 33's and 35's were designed
to be a computer interface, in addition to being a teletype code and
function, and that only about 1/3rd of the possible ASCII codes had been
used in the model 33's and 35's!  Therefor, the "Escape" key was put there
to "escape" from teletype communications functions and enter into computer
functions as computer engineers might want to come up with.

The Control D disconnect function was put on these machines for a reason, .
Pushing the "end" or "disconnect" button on a TWX only had the function of
killing the outgoing data set (modem) tones which either the TWX or
telephone systems, whichever they were used on, would recognize as a carrier
loss, a malfunction, and cause a disconnect.  However this type of a
disconnect took a couple or three seconds, and couldn't be put intro the
tape nor set up as a pre set code.  The Control D function set up a
disconnect code function both in the tape and simultaneously set up machine
functions at each end to initiate the machine's disconnect simultaneously
from each end, which was instantious.  This speeded up the communications
process.

The ENQ was the same as a WRU key, which meant "Who Are you", which sent an
interrogation signal to the distant end which triggered it's "Answer back"
("music box?) system which identified the terminal at the distant end.
Contrary to the operator setting up this coding, this was a technician
function as the operator wasn't trained in this matter, didn't have the
ASCII code, lacked the "drum" where the code was programmed, and the
operator setting this up would risk voiding the maintenance contract with
the customer!  This "Answer Back" enabled "proof" that a message had
actually been received at the unattended distant end by exchanging "answer
backs" at both the beginning and end of the message, assuming that it had
sufficient paper to do the job, and that it's "paper out" compacts were
working to kill the incoming call if the paper ran out.

Control Z was a "End of File" indicator as is still used at the end of
computer programs, etc. This and NNNN (4 N's) was also an International
signal that disconnected the call and turned off the radios used to convey
the message in International radio message traffic.  This is (or was)
necessary with RCA, ITT, WUI, MacKay Radio to ships at sea, etc..

Dick, W7TIO