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NOTE:
Point- to - Point with Line Control.
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Visual References
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NOTE:
Point-to - Point without Master Station and Line Control.
Figure 33.
Point-to-Point Operation
erations, the line correction and line correction release
special features should be installed. Normally, if a
sending terminal fails to transmit a message success-
fully, its data check light and resend light are turned
on and the terminal cannot send again until the resend
light is manually tu,rned off.
With the line-correction feature, two additional at-
tempts to transmit are made. If still unsuccessful, the
line-correction-release feature turns off the resend light
and starts transmission of the next message. In this
case, messages that failed to transmit correctly from
the tape or card reader are not identified in any way
at the sending terminal. However, at the receiving ter-
minal, incorrect messages are indicated by printed
hyphens, an absence of an 11-punch in column 81 of
the punched cards, and three message deletions in the
punched paper tape.
Multipoint Operation (Figures 34 and 35)
Polling
The master station polls other stations with output
units by these methods:
Keyboard
All the required polling characters must be manually
keyed and EOT
@
must be keyed before each station
polling address:
@
A6,
CS)
B6,
@
C6, etc. This is
true for both a polling or an addressing operation. Be-
fore actual polling, assign a master-station printer to
send-receive by positioning its assignment switch. (This
provides line monitoring for recording the stations
polled, polling responses and negative LRC answers.)
A polled system must respond within two seconds. If
no response is received, keyboard polling can proceed
after this interval.
Once the master station has polled another station,
the master-station keyboard is locked and remains
locked during the reception of text until the EOT
@
code is received. This code unlocks the master-station
keyboard to permit further polling. The keyboard is
also unlocked at the end of a 20-second (minimum)
time-out when the master station fails to receive a
character during text transmission. In this instance, the
master station data-check light is turned on. To con-
tinue polling, press the data-check button (to turn out
the associated light) and key another polling address.
The third condition that causes the keyboard to unlock
is an unsuccessful poll (negative response or no re-
sponse within 2 seconds).
Paper-Tape Reader
The polling characters for all stations to be polled on a
communications line are punched into an endless tape
loop:
@
AB,
©
B6,
®
C6, etc. (When preparing
65
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