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Forward Upper, Seek Reverse Lower precedinq
Seek Reverse Upper or Cylinder Out Lower
preceding Cylinder Out Upper.
State Violation (OSl, bit
2 3 )
results from
any of
the
followinq:
1
G
WRr
or WRT
'rEST
while not
On
Cylinder.
2. Set Oiaqnostic Escape with Positioner
Busy.
3. Positioner Busy and anyone of several
coJlllDaJ1ds (seeks, WRT, etc.)
4.
Standby mode (Not Unit Ready)
and
any
one of several commands.
So
Positioner Overtravel (OS3, bit
2
6
)
occurs if the positioner moved into the
forward or reverse End of Travel area.
This may be considered as a OLI Fault
since this most likely occurs if the
Seek Forward Lower or Seek Reverse Low-
er command called for an excessive
seek length.
Oevice Fault Conditions
The followinq conditions are considered as
Device Failures (SSR, bit 21).
FLT is also
qenerated.
toss of Voltaqe (DS2, bit 2°) can occur if
-16 volt emerqency retract voltage is in-
sufficient with the heads loaded.
This also
causes retract relay KS to open, retractinq
the positioner to unload the heads.
The
Pack Unsafe FF sets: the CHECK Indicator
Liqhts.
Spindle Speed toss (OS2, bit 22) indicates
that speed dropped below 3000 rpm with the
heads loaded.
This opens speed relay
K2
which, in turn, opens retract relay KS to
retract the heads.
If speed recovers, the
heads relead.
InsuffiCient speed prior to
heads loading prevents K2 from settinq: First
Seek Interlock cycles are continuous and the
heads never load.
If no head is selected (Head Address Register
contains head 19 or greater), Current Fault
is generated.
This causes the following:
1. Pack Unsafe FF sets the light the CHECK
indicator.
Heads do not unload.
2. No or Multiple Head Selection (OS2, bit
24)
is on.
Read or Write Gate up while not On Cylinder
sets the Pack Unsafe FF and lights the CHECK
indicator.
3-64
Seek Incomplete (DS3, bit 2°) sets if On
Cylinder is not obtained within SOO milli-
seconds after the initiation of a seek or
RrZ function.
It also sets if On Cylinder
1s lost without seek initiation.
If dibits are not sensed within 200 milli-
seconds after the toad latch sets, or if they
are
lost for 200 milliseconda after the heads
are loaded, the
No
Servo Track
'tF
sets. This
causes the following:
1. Pack Unsafe FF sets to liqht the CHECK
indicator.
2. R!Z latch sets to start an
~ZS.
3. With
the
Pack Unsafe condition, the
toad latch cannot set.
(It normally
sets during an
~Z
in the reverse
EOT
area, causing a seek forward to cyl-
inder 000).
Therefore, the heads just
keep going at 7 ips until they unload.
With a Pack Unsafe condition, the drive will
not initiate a First Seek condition (press-
ing START).
Nor will it accept a Seek For-
ward tower, Seek Reverse tower, Recalibrate
or Reset Oiaqnostic command.
The unsafe must
be cleared by pressinq the CHECR indicator
or by a Device Initialize.
Note that a Pack
Unsafe unloads the heads only if dibits are
lost or if -16 volt emerqency retract power
becomes insufficient.
All other CHECR con-
ditions will effectively freeze the position-
er and lock out any further reads or writes.
TRACK SERVO CIRCUIT
GENERAL
The track servo circuit (Figure 3-27) pro-
vides head positioning information.
The
siqnals generated by this circuit:
1. Generate a track servo signal that
indicates the displacement"of the heads
from their nominal track centerline.
2. Generate indications that the heads are
positioned outside of the normal data
cylinders.
3.
Generate cylinder pulses during seeks
to indicate each cylinder crossing.
4.
Provides signals used as the basic 806
kHz clock.
Information for this circuit is derived from
the track servo head (Figure
3-28).
This
head is physically similar to the read/write
heads, except that it does not write.
The
83318200
A
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