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For each line feed operation, the solenoid is energized 15 milli-
seconds for single line feeds and approximately 50 milliseconds for the
double line feed option. At the end of this interval, a 60-90 millisecond
line feed delay is generated to allow the clutch pawl and clutch mechanism
to return home before another paper movement operation is allowed.
In response to a form feed or vertical tab command, a dc level is
applied to the solenoid, allowing continuous movement of the paper.
In
the standard 306 printer, this paper movement continues until it is either
terminated by the reception of a delete code (octal 177) or an INPUT PRIME
signal at the interface connector, or a paper time-out condition. However,
if the optional Vertical Format Unit (VFU) is used, the paper movement is
terminated when a hole is detected in the appropriate channel of the vertical
format paper tape. The operation of the VFU is described in Section 4.7.4.
To prevent the printer from "hanging up" in a paper movement con-
dition which would waste both time and paper, LSI chip 25 contains a paper
time-out circuit. This circuit is activated by any paper movement command.
In the standard 306 printer, the Paper Time-Out (PMTO) interval is factory-
adjusted for approximately 6-9 seconds.
If, at the end of this time, paper
is still advancing, the line feed solenoid command (PMSOL) is immediately
deactivated, terminating the paper movement operation.
As an option, this time-out interval can be adjusted from 2 to 12
seconds via R38 which controls the Low-Frequency Oscillator (LFOC) input
to LSI chip ME25.
As paper moves in the printer, each line advance causes a line count
switch located in the form feed mechanism to open and close. The two wires
from this switch go to the interface connector via the logic card. As a
result, a line count level from the input device is switched on and off by
the printer for each line advance.
If the 306 contains no optional VFU,
the user's software can control vertical formatting by counting these line
count pulses and terminating the paper movement operation when appropriate.
4-24
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