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c. Fine Enable is raised within the
servo circuit.
d. Because of b and c, the Fine gate in
the servo circuit is enabled.
e. The Slope FF is cleared to indicate
a seek to an even-numbered cylinder.
f. Index counter is reset to zero and
held there until the Forward EOT FF
is cleared.
g. EOT Seek Error FF sets.
This re-
sults in steps h through k.
h. Read and Write Gates are disabled.
i. DS3 bit 2
6
(Positioner Overtravel)
is set.
j.
DLI Fault is generated.
Note that
Device Fault is not generated.
k. FLT is returned to the controller.
4.
The track servo, functioning as the fine
servo signal in the servo circuit, is
gated to the servo summing amplifier via
the Fine Gate.
The signal is at a maxi-
mum amplitude because only even dibits
are being sensed.
This error voltage
causes the positioner to drift in re-
verse until the servo signal drops to
zero: the heads are then positioned at
cylinder 822 or 410 for BR3E4/3Es.
The
EOT FF is cleared by the odd dibits.
5.
The positioner has 500 milliseconds to
generate On Cylinder at cylinder 822 or
410, for BR3E4/3Es, for the time that
the Forward EOT FF set.
If not, Seek
Incomplete (DS3 bit 27) and Device Fault
are also generated.
6.
When On Cylinder is generated, Positioner
Busy status drops and DEN is returned to
the controller.
7. To clear the fault, the controller must
issue a Recalibrate or Device
Initializ~
Status clearing requires a DS3 command.
Reverse EOT indicates that the heads are po-
sitioned over the outer guard band.
If this
condition occurs during regular reverse seeks,
the Reverse EOT FF sets.
This initiates an
automatic Load sequence to return the actua-
tor to cylinder 000.
The same error condi-
tion exists, however, as if a forward EOT
occurred.
SEEK STATUS AND ERROR CONDITIONS
General
Many of the status bits available for the
Summary Status Request (SSR) or Detailed
Status (OS) commands are related to the seek
83318200 C
functions.
These conditions are listed in
the following paragraphs.
For further in-
formation on their effects, refer to Sense
Operations.
Normal Status Conditions
The following status conditions are not, in
themselves, considered as errop conditions.
They may, however, shake up the system if
there is an element of surprise in them.
Positioner Busy (SSa bit 24) is up under any
one or more of the following conditions:
1. Unit is not Ready but Stop is down
(generally a First Seek sequence).
2. Stop up with heads still loaded
(generally a shutdown sequence).
3. Zero length seek in Seek Forward or
Seek Reverse Lower.
4. Not On Cylinder.
5. Shift Positioner Out.
Shift Positioner
In or Return to Centerline command:
status is up for 10 milliseconds.
Device Event Notification is generated
when Position Busy drops.
Device in Standby (SSR, bit 2 5 ) means that
Unit Ready is not up (First Seek completed
to On Cylinder) and that stop (SSS or press
START switch to turn it off) is up.
Unit
Ready is not affected by error conditions.
This FF remains set until the heads unload.
Forward FF Set (OS4, bit 21) is up following
·and Seek Forward Lower.
It remains up until
an Seek Reverse Lower is issued.
Note that
the FF remains up and is not cleared by
Recalibrate or other commands.
Reverse FF
Set (DS4, bit 2 0 ) is actually the output of
the reset side of the Forward FF.
Fine Servo Status (OS4, bit 27) indicates
that the Fine FF is set.
This indicates that
the heads are within one-half track of On
Cylinder (or already there) or that the unit
is in a First Seek or RTZS sequence.
Status
drops at Start Seek.
Positioner Offset (OS5, bit 22) indicates
that the unit is still under the influence
of Shift Positioner Out or Shift Positioner
In.
Device Level Interface Errors
(OU)
The following conditions are considered as
oLI Faults (SSR, bit 2 3 ).
FLT is also gen-
erated.
Invalid Command Sequence
(051,
bit 24) is the
result of Seek Forward Lower preceding Seek
3-63
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