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Abnormal Stop Conditions
Operator Intervention
Power-On-and-Reset Pushbutton
Depressing the power-on-and-reset pushbutton while the
2671 is reading causes a general reset. The 2671 stops, all
lamps turn off (except power-on), and the unit-check status
is generated.
Load Switch
Retracting the tape guides by pressing the load switch while
a read operation is in process causes a reset condition. The
2671 stops and generates channel-end and device-end and
unit-check. The ready lamp turns off, and the buffer and
data register are cleared.
Without Operator Intervention
The 2671 stops during a read operation when abnormal
conditions occur internally or in the system.
By the System
The 2671 stops when the emergency switch (located on the
System/360) is operated. All power, both ac and dc, is
removed from the 2671.
When a halt I/O is initiated by the System/360, the 2671
stops on the second character following the last character
sent to the System/360 (in the same way as for a channel
contention). The 2671 remains ready and a channel-end
and device-end status byte is generated.
When a selective or general reset is initiated by the
System/360, the 2671 stops immediately and all functions
of the 2822 are reset except the buffer and the data regis-
ter. No status byte is generated and the 2671 remains
ready.
By the 2671
If the 2671 stops with the ready and equipment-check
lamps on, a timeout has occurred because the last character
was transferred to the system.
If the 2671 stops with the ready and data-check lamps
on, a parity error has occurred.
Overstep
Overstep is that condition where a character on a tape over-
shoots the read head slightly, owing to the maladjustment
of the brake or the drive clutch; it will always require inter-
vention by the IBM customer engineer.
Each time an overstep condition occurs, the overstep
lamp lights and the ready lamp is off, regardless of the state
of the other lamps.
Note: Owing to the thermal inertia in the lamp control
feedback circuit, the overstep lamp may light when the load
switch is set on and then off. In this case, operate the
power-on-and-reset pushbutton to clear the error.
ERROR RECOVERY PROCEDURES
The following fault conditions require operator inter-
vention. If simultaneous fault conditions occur, assign
error-recovery priority in the following order:
1. Equipment check.
2. Intervention required.
3. Data check.
Equipment Check
If a tape jam has occurred, it is necessary to free the tape
and splice the damaged areas. After repair, the tape may be
positioned at the beginning of the tape, of the record, or of
the next record. The 2671 must be reset, then made ready,
so that reading may continue.
Intervention Required
An intervention-required error is caused by any of the
following conditions:
1. If the 2671 is not ready or the power-on-and-jreset push-
button has been pressed during reading.
2. If the load switch has been pressed during reading.
3. If the tape has broken.
It is necessary to reposition the tape (after repair if neces-
sary). The tape may be positioned at the beginning of the
tape, of the record, or of the next record (as required). The
2671 must be reset, then made ready, so that reading may
continue.
Data Check
If a data-check error occurs, any of the following oper-
ations may be undertaken:
1. The tape may be backspaced two characters.
2. The tape'may be repositioned at the beginning of the
record.
3. The tape may be repositioned at the beginning of the
tape.
4. The error may be ignored completely.
For each of these operations, the 2671 must be reset,
then made ready, so that reading may continue.
Abnormal Stop Conditions
17
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