Functional Description; Hp 7925 Disc Drive, Simplified Block Diagram - HP 7925D Service Manual

7925
Theory of Operation
operation and appends it to the other information written
in the sector. The check information itself depends on the
value of every bit from the first bit in the sync word to the
last bit in the data field. During a read operation, this
check information is regenerated and compared in such a
way that the presence of errors is detected, and by using
the error correction hardware in the controller, the
error(s) may be corrected.
The HP 13356A Formatted Disc Pack is formatted in this
fashion and it must be used as the removable storage
media for this disc drive.
1-7. FUNCTIONAL DESCRIPTION
The disc drive is organized into eight functional systems.
(See figure 1-6.) These are the input/output
(I/O)
control
system, spindle rotation system, head positioning system,
sector sensing system, read/write system, fault detection
system, air circulation and filtration system, and power
distribution system.
Each of these functional systems is discussed in detail in
the following paragraphs. In addition, a functional block
diagram is provided for each system in Section IV,
Troubleshooting. An alphabetic listing of each signal
mnemonic, a source and destination signal list, and a
mainframe wiring diagram are also provided in Section
IV, Troubleshooting.
The I/O control system provides the communication link
between the controller and the disc drive via its tag and
control buses. The spindle rotation system provides power
to the spindle motor and maintains spindle speed at 2700
revolutions per minute. It also operates the pack loading
assembly door lock mechanism. The head positioning sys-
tem controls the loading and unloading of heads under
both normal and abnormal (fault) circumstances. The sec-
tor sensing system continually monitors the physical sec-
tor presently passing beneath the heads. The controller is
notified when the present sector equals the addressed sec-
tor. This information is also used to enable the read/write
system for a data transfer operation. The read/write sys-
tem provides the means to read information from a data
surface or write information onto a data surface. The fault
detection system continually monitors various conditions
within the disc drive, and lights fault indicators, retracts
the heads, and brakes spindle rotation when a fault is
detected. The air circulation and filtration system pro-
vides cooling air to the heat generating components of the
disc drive and cool filtered air to the pack chamber. The
power distribution system supplies all operating voltages
to the seven other disc drive systems.
r---------------------------------------------------,
HP 7925 DISC DRIVE
DISC
PACK
ENCODER
DISC
ACTUATOR
ASSEMBLY
SPINDLE
ROTATION
SYSTEM
LIGHT
FAULT
INDICATORS
RETRACT
HEADS
HEAD
POSITIONING
SYSTEM
BRAKE
f - - - - S P I N D L E - - - . '
SERVO ...-----+-----
CODE - - - - - - - '
SECTOR
SENSING
SYSTEM
FAULT
DETECTION
SYSTEM
TO ALL
OTHER
SYSTEMS
I/O
CONTROL
SYSTEM
POWER
DISTRIBUTION
SYSTEM
AC
~N:~~ ~
II'
POWLER r-
A
-
I
-
R
-CI-RSC-Y~-~A-~~-I:-N~
& FILTRATION
I
SYSTEM • • •
I
I
I L
--l
4
_-,;,L..<_ - , - - _
~~~--.
- - - - - STROBE-----..
11
_-,;<-'........
--:--_CO~~~O
L
----+L..-_-....._ _
....J
i
SECTOR CLOCK
&
INDEX
I
READ/WRITE
I
- -......
-------4----~I~~~-----~
. ..._ _
S_YS_T_EM_---'I+~
- - - - D A T A
- - - + ,
FROM
PR~~~~~ -:--_+_~
SOURCE
TO/FROM
CONTROLLER
7311-37
Figure 1-6. HP 7925 Disc Drive, Simplified Block Diagram
1-5