4.7.1.4 Logic Schematic, Sheet Five
The
functions shown
on
sheet five
of
the Logic schematic consist entirely of sector
electronics. These functions consist of the upper sensor detector, the upper time
demultiplexer, the lower sensor detector, lower time demultiplexer, sector phase lock
loop, upper sector countdown, lower sector countdown, sector multiplexer, index
multiplexer, sector pulse formers, index pulse formers, upper sector number counter,
lower sector number counter, sector count multiplexer,
and
the multiplexer control.
4.7.2 DISK
DRIVE
FUNCTION CONTROL
The Disk Drive Function Control Logic is one
of
the major sub-divisions
of
the disk drive
which require logic for the control
of
functions performed. Figure 1-4 is a functional block
diagram
of
the 03000 Disk Drive and should be referred
to
in conjunction with the
following paragraphs.
The
major block identified as Disk Drive Function Control in Figure 1-4 can
be
sub-divided
into two parts: a major block consisting
of
the Start/Stop Control, and a minor block
containing minor control functions, e.g., head select control, unit select decoding. The
following paragraphs contain a functional discussion of these blocks.
4.7.2.1
Start/Stop Control
Essentially, the Start/Stop Control is a digital sequential machine mechanized with
integrated circuit logic. The purpose
of
this logic is to take external commands, combine
them
with internal conditions plus suitable timing, and generate output signals for control
and indication purposes. Figure
4-8 Is a block diagram
of
the digital sequential machine
used to mechanize the start / stop control.
The three essential blocks, shown in Figure 4-8, are
State Storage, Combinational Logic,
and
Delay Generator.
The
purpose of the State Storage block is to store the machine
states, This is mechanized with flip-flops
and
a counter.
The
present states are combined
in the Combinational
LogiC
with external commands which allows the generation
of
output
signals for indication and control
by
the output signal combinational logic. All of the
combinational logic is mechanized with gates.
It should
be
noted that external commands
can
modify directly the stored states. This is in addition to the capability
of
external
commands in combination with the present states
to
provide output signals and
modification
of
the stored states.
Included
in
the block diagram is a Delay Generator which is mechanized with counters and
a flip-flop. The generator provides specific delays under control of certain of the
Combinational Logic output signals.
The
Time Reference to the Delay Generator is
obtained from a crystal oscillator and clock countdown circuits.
Figure 4-9*
is
a functional block diagram of the Start/Stop Control. Ail
of
the logic
depicted in this figure is contained
on
sheet two of the Logic PCBA schematic. The time
reference for this arrangement is provided by a
Crystal Oscillator whose output signal is
frequency divided by the
Clock Countdown circuitry. This circuitry consists of a series
chain of counters that generate clock signals that are used
by
the Start/Stop Control logiC.
These clock frequencies are also used in other portions
of
the disk drive logic.
Within the
Start/Stop Control, gating
of
the clock signals is accomplished by allowing
clock pulses to
be
fed
to the flip-flops only at specific times, thereby permitting these
flip-flops
to
change state only when a clock pulse is present.
The
delay generation portion
*Foldout drawing,
see
end
of
this section.
4-17
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