[GreenKeys] 28 typer with a pretty full stunt

[Jim Haynes]

On Fri, 15 Jun 2018, tony.podrasky wrote:
> I don't recall what the option was named - but I had
> one 28-ASR that would run, making all the noise like a
> regular one but without actually printing - and then when
> it received the correct code, would print messages until
> it received the NNNN sequence.
>
It's called Selective Calling, where it takes a certain sequence of
characters to make a printer print, all others on the same line are
nonprint, and then the end of message code puts them back into the
regular case.  The fact that it requires NNNN suggests military.

The FAA was a big user of this feature, but they did not use the
NNNN sequence - rather it was the three letter station identifier
(about the same as a three-letter airport code) that enabled printing.
And most of the FAA machines had a solenoid on the left end plate that
would put the machine in condition to print everything.

In some systems there might have been more than one code to enable
printing, as there might be a code to turn on a certain group of printers
in addition to one for the individual printer.