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When the disk pack speed reaches 3,000 rpm,
the power supply relay K2 energizes to apply
+20v power to the read/write logic and to
energize retract relay
XS
(the
heads are un-
loaded) to connect the positioner voice coil
to the power amplifier driven by the servo
logic.
At the end of the 15 second (approximately)
First Seek Interlock Cycle the First Seek
Interlock switch transfers and activates the
first seek operation by setting the Load
I
latch.
In
SIC 33
and above, first seek delay
circuit on the _SAV card provides the
signalthat sets the Load
latch~
Th~
Load
latch drives the Load gate:
th~s b~as
voltage forces an average forward 7 ips
access that mechanically loads the heads.
The carriage continues forward with the
servo head searching for the prerecorded
positive dibits signals on the track servo
or positive, dibits) is sensed, the Load
latch is cleared and the Fine gate is en-
abled.
The carriage now servoes into
cylinder 000 under control of the fine servo
signal.
When the positioner reaches cylinder 000,
On
Cylinder is generated.
This causes the fol-
lowing sequence of events:
1. Unit Ready comes up within the drive.
2. Standby status drops.
3.
Positioner Busy·status drops.
40 DEN is returned to the controller.
s.
With EOT down, Index is available.
6. The drive may respond to any operational
command if preceded by a normal seize
sequence.
However, Seize and
S~
Status Request (Tag 28) do not
requ~re
a prior Unit Ready.
If
for any reason, the dibit signals are not
de~ected
by the track servo logic within 200
milliseconds after the Load Latch is set, the
RTZ latch will be set.
The positioner will
retract to the heads unloaded position.
In
this case, a Pack Unsafe (Device Fault and
CHECK indicator on) condition exists to pre-
vent reloading until the CHECK is cleared.
The same conditions exist if the dibits are
lost for 200 milliseconds after Unit Ready
is available.
Refer to Seek Status and
Error Conditions for other First Seek Errors.
Direct (Forward/Reverse) Seek
Introduction
The Direct Seek function involves those oper-
ations that must be performed to move the
read/write heads from their present track or
cylinder location to the one specified by
the controller.
This function must be pre-
ceded by a Seize command unless the unit is
already seized or if it is a single channel
device.
3-52
The basic principles of the seek operation
are explained in the Servo Circuit discussion.
•
I/O Sequencing
Controller/drive Signal interchanges during
a seek function frOID cylinder 10 to cylinder
160 would be as follows (see Figures 3-23
and 3-24):
Except as specified below, the
actual sequence may be varied
without affecting drive opera-
tions.
This is a typical se-
quence.
1. Controller raises Cylinder Address
in
Opper (Tag 22) command.
a. Drive decodes command.
b. Bit 2
8
and 2
9 .
of Cylinder Address
Register is placed on bit 20
and
21
of bidirectional data lines.
This
bit
is
on if the positioner is
currently at cylinder 256 or above.
Since the current address is 10,
bit 2 0 and 21 are zero.
c. Drive raises Serial Read In one
microsecond after rise of Device
Command Strobe.
Delays
OC,3
and
DC,4 must time out before Serial
Read In is raised.
It drops in
response to Serial write OUt from
the controller.
2. Controller raises Cylinder in Lower
(Tag 23) command.
a. Drive decodes command.
b. Bits 27 through 2 0 of Cylinder Ad-
dress Register are placed on bi-
directional data lines.
With current
address equal to decimal 10, this
byte is 0000 1010.
c. Drive raises Serial Read In.
It
drops in response to Serial Write
Out.
3.
Controller places bit
2
8
and
2 9
of
new address on bit 20 and 21 of bi-
directional data lines.
Since new
address (160) is less than 256, this
bit is zero.
Controller also raises
Cylinder OUt Upper (Tag 06) and Serial
Write Out.
a. Drive decodes command.
b. Drive raises Serial Read In.
83318200
E
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