Disc Drive And Controller - HP Integral Personal Computer Service Manual

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An HP-HIL (Hewlett-Packard Human Interface link) keybotqd interface, IC US8 on the logic A PeA,
controls the keyboard. The keyboard plugs into either one of the two HP-HIL jades on the front panel
(lower left) of the computer.
The number of HP-HIL devices (for example, a keyboard and mouse) that can connected to the rom-
puter depends upon the
power
drawn by the individual devices. (The Integral PC keyboard draws 100
mA)
The totlll power drtnDn by all HP-HIL devices connected to the
two
jacks must not aceed
600 mAo
The HP-HIL controller can configure up to seven devices if they do not exceed the power rating.
5.11 Disc Drive and Controller
The Integral PC includes a double-sided 3Y2-inch miaofloppy disc drive. The disc control circuitry
includes a Western Digital 2797 floppy disc controller IC (Ut8 on the logic B PCA) and associated
logic
circuitry.
Figure 5-4 is a block diagram of the disc drive and controller.
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1----------------.
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1 I
~
______
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____
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I
SVSTEM
CONTAOL
I
I
I
I
I
I
DISC
CaNTADLLE
(Ull.,
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LOGIC 8 PeA •
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FI .... 5-4. Disc Drive Block D .......
DISC
DAIVE
- - . - . . CDNTAOL CIRCUITS
The disc drive routine resides in operating system ROM. It contains a software loop to control data
transfer.
The disc drive uses double-density recording in accordance with the Hewlett-Packard MFM (modified
frequency modulation) format.
Each disc drive assembly consists of a drive mechanism, a read/write head, a head· positioning mecha-
nism, the control interlocks, and a PCA containing the electronic components. The read and write
circuits, the head-position control circuit, and the read, write, and erase enable circuits are all located
on the disc drive peA.
The disc drive motor operates only du.-ing a disc access.