[GreenKeys] Model 35

[Jim Haynes]

On Sat, 23 Jul 2011, Larry Tighe wrote:

> Still working to understand the Model 35 I aquired.....why would the machine
> have a "KB Unblind" function.
>

Well, let's go back to the Model 15 KSR.  Most of those have a
SEND-RECEIVE-BREAK switch, and when you receive a break it goes to the
break position and shorts the keyboard.  That gets your attention that
the operator at the other end needs to interrupt your sending for some
reason.  When that is settled you have to manually move the switch back
to the SEND position to resume sending.  Otherwise it is in the RECEIVE
position and your keyboard stays shorted.

Now in the Model 28 KSR there is a mechanical keyboard lock, which can
be configured so that when you receive a break the keyboard locks and
you realize right away that you aren't sending.  You have to manually
push the keyboard unlock key to restore your ability to send.

I would assume a similar feature exists for the Model 35, but I don't
remember them well enough to know for sure.

Those are cases where the keyboard is locked or blinded to interrupt
you when you are sending.

Now there are other kinds of terminals, such as the IBM 2741, which
automatically lock the keyboard after you hit the ENTER key, and you
can't send any more until the computer you are connected to sends a
signal to unlock the keyboard.  I have a wry saying that in the older
IBM world the only input device is a card reader, and it doesn't read
a card until it is told to.  So they make a terminal behave like a card
reader by not letting it send any input until the computer tells it to.

So blinding the keyboard by shorting it might be a less complicated way
of locking the keyboard so the operator can't send.  This could be used
with any kind of computer system that doesn't allow un-asked-for input.

Then, and I have no direct experience with this, there was the period
when TWX had a mixture of 100 wpm Model 33/35 machines and 60 wpm
Model 15/28 machines.  Sending from either machine to the other had to
go through a speed converter.  That's no problem if you are sending from
a slower machine to a faster one.  Going in the other direction there
was a limited amount of buffer storage in the speed converter, so there
was a "restrain" signal to tell the operator at the faster machine to
quit sending for a while until the buffer empties.  I don't know if the
restrain signal locked the keyboard or blinded it or just gave the
operator a caution light signal.