Tape Position Markers - IBM 5100 Maintenance Information Manual

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Tape Position Markers
The following illustration shows the position of the holes
(markers) on the tape. These holes generate a BOT
(beginning of tape) status and an EOT (end of tape)
status.
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Forward Tape Motion
BOT Load Point Hole
3 Feet
o
EOT
Physical Beginning of Tape
BOT Markers
The top five holes in the preceding figure all generate a
BOT status when they are sensed. BOT status is sensed
when infrared light from the LED passes through any of
the top holes and is detected by a PTX.
The load point and early warning BOT holes are slightly
smaller than the other three BOT holes. Therefore, in a
failing condition, the PTX might detect the light coming
through a large BOT hole but not detect the light
coming through the smaller load point or early warning
BOT holes.
The load point hole indicates the beginning of the
recording area on the tape. The early warning hole
indicates the end of the recording area on the tape.
Early Warning Hole
3 Feet
o o o
. .
EOT
Physical End of Tape . /
EDT
Markers
The bottom six holes in the preceding figure all generate
EOT status when light from the LED is sensed by the
PTX. All of these holes are the same size.
Physical Beginning and End of Tape
The physical beginning and end of tape are determined
by using both the BOT and EOT status. The beginning
of tape has three groups of both BOT and EOT holes.
Therefore, at the beginning of tape, both a BOT and an
EOT status are sensed. The end of tape has three EOT
holes only. Therefore, at the end of tape, only EOT
status is sensed.
The normal customer operation of the tape unit uses
only the load point hole and the early warning hole. All
information is recorded between these two holes.
Sensing an EOT hole is an abnormal condition indicating
that the load point or early warning hole was not found.
EOT status stops the tape drive. The three EOT holes
on each end of the tape ensure that EOT status is
sensed and prevents the tape from running off either
reel.
Tape 4-37