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preceding operations will be repeated.
Should a Read signal be applied to the TTY under conditions whic.h prevent
generating a Read Enable signal (i.e., Data Read FF clear or Write Mode FF set),
a Reject is sent to the computer.
LOST DATA
If the contents of the Data Holding Register have not been transferred to the
computer before another keyboard line transfer occurs, the Lost Data FF (page 17)
will be set by the Start signal entering the controller from the keyboard line.
When the Lost Data FF sets:
(1)
a lost data Status is produced (17-C14-20).
(2)
the Break FF (page 17) sets.
(3)
a 180 msec time delay is started.
Setting of the Break FF prevents the keyboard entry from transferring into the
Holding Register (page 23).
The Break FF also holds a Busy status throughout
the 180 msec delay.
These two operations insure that previously held data will
not be destroyed and that this data cannot be read during the 180 msec time
delay in progress.
During the 180 msec delay period, the keyboard becomes locked so that other keys
cannot be depressed, the paper tape reader (if running) is stopped and a BREAK
light on the TTY console is illuminated.
The period of 180 msec without trans-
mission is equivalent to a NULL-NULL Code which will cause remote stations to
disconnect.
To unlock the keyboard, it is necessary to press the BREAK
REL
(Break Release) button on the keyboard.
This also turns aff the BREAK light.
Even with the keyboard unlocked, read operations cannot continue until the Lost
2-21
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