[GreenKeys] Stop bit

[Jim Haynes]

Western Union had a little gadget called Open Line Stop that could be 
added to the selector of a Teletype machine.  What it did was to detect,
by contact closure, a spacing signal at a time when the stop pulse is
expected.  And do it early enough so a relay could close the line and
prevent the machine running open.  The application was in the Plan 21-A
switching system (see Western Union Technical Review) where timed break
signals were used to control the outstations.  Open Line Stop on a
station operated full duplex allowed these break signals to be transmitted
in the middle of traffic.  The printer would see the break signal as a
blank and would not print a garbage character in the middle of the
message being received.



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 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man