5 1/4-Inch Diskette Drive Adapter
The System Unit has space and power for one
or
two
5-1/4"
Diskette
Drives. The drives are soft sectored, single sided, with
40 tracks. They
are Modified Frequency Modulation
(MFM)
coded in
512
byte
~
sectors, giving a formatted capacity
of
163,840 bytes per drive. They
have a track to track access time
of
8 ms and a motor start time
of
500 ms.
The
5-1/4"
Diskette Drive Adapter fits in one
of
the System Board's
five System Expansion Slots.
It
attaches to the two drives via an
internal daisy chained flat cable which connects to one end
of
the drive
adapter. The adapter has a second connector on the other end which
extends through the rear panel
of
the System Unit. This connector
contains the signals for two additional external drives, thus the
5-1/4"
Diskette Drive Adapter is capable
of
attaching four
5-1/4"
drives, two
internal, and two external.
The adapter is designed for double density
MFM
coded drives and uses
write precompensation with an analog phase locked loop for clock and
data recovery. The adapter
is
a general purpose device using the
NEe
IlPD765 compatible controller. Thus the drive parameters are
programmable.
In
addition, the attachment supports the drive's write
~
protect feature.
The adapter
is
buffered
on
the
I/O
bus and uses the System Board direct
memory access
(DMA)
for record
data
transfers.
An
interrupt level is
also used to indicate operation complete and status condition requiring
processor attention.
In
general, the
5-1/4"
Diskette Drive Adapter presents a high-level
command interface to software
I/O
drivers. A block diagram
of
the
5-1/4"
Diskette Drive Adapter is on the following page.
2-89
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