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"reset write triggers" pulse could coincide with the fall of a write pulse. In this case
(Case B, Figure 30) assuming all ones were being written, at time T^
write triggers might be turned on and some might be turned off.
would be flipping out of step with each other for the rest of that writing period.
condition could be observed at the write trigger neons when the writing is stopped.
Usually, however, (as in Case A) all triggers are either on or off.
observing the write trigger neons shows whether the triggers are operating properly.
1 9.3.3
Reading
To read a tape, set the read-write switch to READ and press the start button.
Tape moves forward in read status.
the response select switch can be observed with a scope at the read bus hub.
pressing the stop button stops the operation.
When in read status, the tape is read in start-stop fashion if the start-stop
switch is turned on.
The start-stop frequency dial controls the frequency of starting
and stopping the tape. Unless the manual switch is used, tape cannot be read when
the tape indicator is on.
1 9 .3 .4
Auto Cycle
The auto cycle feature on the TDT may be used to check the following operations
of the tape drive: end-of-tape sensing, load-point sensing, high-speed rewind,
vacuum switches, and flapper valves.
write the tape in a forward direction until an EOT reflective spot is sensed.
chine then rewinds the tape back to the load point.
tape unit starts writing again and the cycle is repeated.
This operation is accomplished in the following manner; upon sensing the EOT
reflective spot, the signal "s e l and TI on" goes through section E of the response
select switch and back to the tape drive as "rew in d ." This signal causes the tape
to rewind, and the signal "select unit rewinding" com es from the tape drive through
section D of the response select switch and returns to the tape drive as "reset T I,"
thus turning off the tape indicator.
nects the "select and TI on" line that normally turns off the go-fb trigger. When the
tape is rewound to load point, the ready line com es up and the tape drive starts writ
ing again.
To put the machine into the auto cycle operation, the response select switch is
set to AUTO CYCLE and the read-w rite switch is set to WRITE.
button then puts the tape drive into auto-cycle operation.
spot a few feet from the load point, the cycle can be made very short and the load
point and EOT photo cells and single shots can be checked. If the EOT reflective spot
is placed farther back on the tape so that the tape drive can just go into high-speed
rewind upon sensing the spot, and the load point is placed just before this area, then
the operation of the vacuum system and associated switches can be observed at a
frequent rate.
With a full reel of tape on the tape drive and the EOT spot at the end of the tape,
the tape drive can be auto-cycled to check the rewinding of a full reel at high speed.
The pre-am p output of the track selected by
The function of the auto cycle feature is to
Upon reaching the load point, the
Section F of the response select switch discon
By placing the EOT reflective
82
some of the
qq
Then these triggers
This
Therefore,
De
The ma
Pressing the start
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