6300
4.7 LOGIC FUNCTIONS AND CONTROL
There
are
five major areas in the 03000 Series Disk Drives which require logic for control
of
functions and timing, these are: Disk Drive Function Control, Read/Write Electronics,
Spindle Speed Control Electronics, Position Control Electronics, and Sector Electronics.
They
are
functionally shown in Figure 1-4. Since the majority of logic in the 03000 is
packaged
on
the Logic PCBA, the following is primarily a functional description of the
Logic PCBA.
Only those areas on other circuit boards having logic functions of interest
are
included.
NOTE
In
order to
fully
understand the
logic
functions described,
the reader
should
acquaint
himself
with the discussion
of
the specific integrated circuits contained if) Section
V.
He
should
a/so become
familiar
with the schematics
contained in
Section
VII.
4.7.1
LOGIC ARRANGEMENT
The Logic PCBA is depicted
on
sheets 2 through 5 of Schematic No.1
02830.
These sheets
have
been
divided
on
the basis of function and, therefore, a specific sheet is a complete
(or nearly complete) schematic representation
of
a specific function. The following
discussion
Identifies these functions
by
schematic sheet number.
4.7.1.1 Logic Schematic,
Sheet Two
Sheet two of the Logic schematic contains the
StartlStop
Control which is used in the
control
and
timing process
of
executing the start cycle
of
the disk drive and for executing
the stop cycle of the disk drive. Also shown on this sheet is the main clock generation
circuitry which consists
of
the crystal OSCillator, clock countdown and clock gating
circuitry. This arrangement provides the reference for all timing functions
on
the LogiC
PCBA.
A subdivision of the
StartlStop
Control is also included. This circuitry is used for the
detection of
run/stop
commands, emergency and fault mode control, interlocking control,
start cycle sequencing, stop cycle sequencing, and condition indication.
4.7.1.2 Logic Schematic,
Sheet Three
Sheet three of the Logic schematic contains a number of minor functions; these
are
the
select enable controls, the
read
outputs, the status outputs, the termination voltage power
supply,
and
the spindle speed control digital logic.
A subdivision of the select function is the head and disk select control, track offset enable
control, write/erase enable control, unit select decoding, busy signal encoding, write
protection control, and the status and indication circuitry.
4.7.1.3 Logic Schematic,
Sheet Four
The
functions shown
on
sheet four of the Logic schematic deal entirely with position
control; these are the demand address register, the valid address decoder, the current
address counter, the
count
control, subtractor and complementor, carry control, the load
address
and
illegal address control, busy logic, mode control, operation control,
and
error
check logic.
4-16
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