IBM 727, Руководство по инструкции

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11.4 TAPE INDICATOR 75. 03
The tape indicator is a trigger that may be used to indicate certain conditions
sensed within the tape unit. It may be controlled externally or internally. The trig­
ger is turned on internally by sensing the reflective spot at the end of a reel of tape,
when writing. The rear photo-cell output is AC coupled to an inverter to pull over a
20ms SST . The plus output of the S S j is combined with write status in AND circuit
B29, turning on the trigger. The trigger may also be turned on by bringing up "turn
on TI" from the control unit if the select line is plus.
The right output of the trigger is combined again with select and becom es "select
and TI on" which is sent back to the external control unit. Also, the tape indicator
light is turned on. "Turn off tape indicator" is combined with select and used to turn
off the tape indicator trigger if it is on. This causes the "select and TI off" line to
come up to provide this indication to the external control unit.
11. 5 TAPE BREAK INDICATION 75.03
If the machine is rewinding at high speed and a break occu rs, provision must be
made to stop the unit. This is done by using the same photo cell that is used for end-
of-tape indication. A light source is brought up from underneath the tape. It shines
on the cell if the tape breaks. The photo cell output is combined with the "rewind
interlock status" line in 75.03 and the output is used to pick a tape break relay (R41)
in 75.09. 03. This is a latch pick relay that remains latched until an unload condi­
tion is initiated. To stop the reel motion, a R41-1 point opens in the circuit of R l,
a run relay. When the run relays drop out, the m otors stop running and the brake is
applied.
Depressing the unload button picks R41LT (75. 09.03) through R22-6 and R41-2.
This places the machine back in normal status.
11. 6 STARTING FROM LOAD POINT 75. 04
To read or write at the beginning of the tape, the start line is brought up as a
result of the go line from the external control. This line is sent to 75. 04 and com ­
bined with "at load point" in AND circuit G20 to produce a line called "drop load
point r e la y ." This picks R19 in 75.09.03. The R 1 9 -ln /o points close to pick the
latch trip coil of R42. As a result of this, "at load point" drops and "select and at
load point" drops. Therefore, unless the tape is rewound, no more load point con­
siderations are made.
11.7 START, STOP, AND REVERSE CONTROL 75.05.01
There are two ways of bringing up the start line, resulting in a start position of
the moving co il. The go line, brought up externally, combined with select and ready
raises the start line, and drops the stop line. Also, raising the manual start line,
combined with "not arriving at load point" raises the start line. This is the combina­
tion used while rewinding and unloading.
There are two ways of bringing up the reverse line, conditioning the machine to
move tape in a reverse direction. The backward line., brought up externally, com ­
bined with "select and ready" raises the reverse line.
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