The specific sectoring configuration is selected by the connections
of
the Sectoring
Selection Programming Array shown as two blocks in Figure 4-17. The raw pulses output
from this interconnection array are unsuitable
for
application
to
the
I/O
interface directly
and must
be
formed into suitable pulses by the Upper Sector Pulse Former, the Lower
Sector Pulse Former, the Upper Index Pulse Former, and the Lower Index Pulse Former.
Each
of these pulse former circuits takes the raw input pulse and converts
it
into a pulse
having a time duration that is suitable for transmitting over the
I/O
interface. The outputs
of the Upper
Sector Pulse Former and Lower Sector Pulse Former are multiplexed onto the
single
Sector Pulse (ISPXD) line by the Sector Pulse Multiplexer according to the
particular platter selected by the
I/O
interface.
Likewise,
the
outputs of the Upper Index Pulse Former and Lower Index Pulse Former
are
multiplexed by the Index Pulse Multiplexer and fed to the single Index Pulse (IIPXD) line
according to the particular platter selected by the interface. The Multiplexer Control Logic
controls the pulse multiplexers according
to
the state on the Upper Platter Select
(LUPSG), the Not-Upper Platter Select (NLUPSG), and the Selected and Ready (NLSARG)
line.
Additionally, the raw pulses obtained from the Sectoring Selection Programming Array
are
applied to the sector number counters
for
purposes
of
generating the sector count. The
Upper
Sector Number Counter and Upper Count Control are used
to
generate the sector
number count
for
the upper platter. The Lower Sector Number Counter and Lower Count
Control are used to generate the sector number count for the lower platter. A particaular
sector count is multiplexed by the
Sector Count Multiplexer logic according
to
the control
signals generated by the Multiplexer Control logic. These control signals, generated by
the Multiplexer Control logic, are a function
of
the specific platter selected and the
Selected and Ready condition. The count control
for
each sector number counter
determines when the counter will be returned to a zero count. This is determined
automatically
as
a result
of
the count control action obtained from the raw index pulse
occurrence.
Electronic pulses are generated by the disk drive as selected by the Sectoring Selection
Programming Array when the removable cartridge has the index slot only, or when it is
desired to electronically sector a multi-notch removable cartridge. Additionally, the
Sectoring Selection Programming Array causes the disk drive to generate pulses
for
sectoring the lower
disk
which is sectored electronically regardless
of
the configuration.
These pulses are generated by counting down, with
an
electronic counter, the output
of
a
high-frequency oscillator. Because the sector pulses must be synchronous with the
instantaneous speed of rotation
of
the spindle,
it
is necessary to phase lock
this
high-frequency oscillator to the spindle.
Those particular functions are implemented by the
Sector Phase Lock Loop through the
Upper and Lower
Sector Countdown Counters. Associated with these counters
are
Electronic Sector Programming Arrays used
to
determine a particular number
of
sectors
and a synchronizer
for
each counter to synchronize the count with the Index pulse
obtained from their respective Time Demultiplexer. The output derived from the phase lock
ring notches
are
fed via the Lower Time Demultiplexer
to
a Phase Lock Flip-Flop which
divides the frequency of that pulse train by a factor of
2,
and converts it into a square wave.
This square wave is used not only by the
Sector Phase Lock Loop but is one
of
the outputs
of the Phase Lock Flip-Flop fed to the
Spindle Speed Control electronics.
The Voltage Controlled
OSCillator (VCO) within the Sector Phase Lock Loop is
electronically servoed to the square wave obtained from the Phase Lock Flip-Flop. This is
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