6300
There
are
two basic types
of
sectoring: mechanical and electronic. The electronic type of
sectoring may
be
further classified into electronic sectoring with the index-only type of
cartridge and electronic sectoring with a multi-notch cartridge.
The
primary inputs to the sector circuits are derived from two sensors located in the disk
drive, and from clock
Signals derived from the Clock Countdown in the Start! Stop Control
logic (sheet 2
of
schematic). The Drive/Motor Enable signal is also used
in
the sector
electronics circuits. The Upper Platter
Select signal and the Selected And Ready signal is
employed to control the output multiplexer. These signals are also obtained from the
Start! Stop Control Logic.
The outputs
of
the sector electronics are the Sector Pulse (ISPXD), the Index Pulse
(IIPXD), and the
Sector Count (ISCOD-ISC6D).
The Sector Pulse (ISPXD) provides a train
of
pulses at regular intervals during each
revolution
of
the disk. These pulses divide the disk surface into
"n'
equal segments, where
'n' is the number
of
pulses and the number
of
sectors.
The
Index Pulse (IIPXD) is a pulse train with a single pulse occurring once per revolution
of
the disk. This pulse always occurs
just
prior to sector zero.
The
Sector Count lines (ISCOD-ISC6D) specify the sector count which is presented to the
II 0 interface in a binary format. This count indicates the particular segment
of
the disk
surface currently under the Read/Write heads. The
Signals on these lines are,
in
essence,
the states of a binary counter and in
all cases correspond only
to
the respective platter
as
selected by the Platter Select Line.
The particular type
of
sectoring
for
which a
disk
drive is configured is determined
by
the
programming arrays that are installed in the Logic PCBA. The parameters that
are
programmed into these arrays determine the nature
of
the sectoring. These parameters
are: type of sectoring, number
of
sectors, and related
disk
speed.
The
type
of
sectoring is programmed by the programming array plug installed
in
J125
(zone
C,
D,
E,
F-14). The values
for
the Upper and Lower Demultiplexer Counters, which
are
relative to the speed of the disk, are programmed by
J121
, shown in zone 15.
The number
of
sectors for electronic sectoring is programmed by J126 and J127 shown in
zones
10, 11, and 12. The electronic sectoring is configured by the programming array
plugs installed in J123 and J124. These arrays determine certain parameters of the
electronic sectoring.
The Upper
Sensor Detector (zone H19) and the Lower Sensor Detector (zone
F19)
receive
signals from the upper and lower sensors, via J112 (zone
E,
F,
G,
H-20), and convert these
analog signals into digital form. The Lower
Sensor Detector
circuit
is similar to the upper
sensor detector except that
it
has the additional capability
of
changing thresholds.
The
Upper Sensor Detector has two amplifiers
U425
and
U387,
which are not required in
the Lower
Sensor Detector. Otherwise, the
circuit
functions are similar. The Upper Sensor
Detector receives the signal derived from sensing
thinto
a digital pulse train. The Lower
Sensor Detector converts the analog signal obtained from the Lower MagnetiC Sensor,
which senses the Phase Lock Ring, into a digital pulse train.
NOTE
The
removable cartridge may be sectored either
electronically
or
mechanically.
The
lower
platter
is
always
sectored electronically in dual
disk
machines.
5-36
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