Block Diagram
Refer
to
figure 3-3.
The
drive electronics/controller
PCA
controls
the
operation
of
the
drive,
including head positioning,
data
transfer, spindle speed, and power distribution.
SCSI Interface
The
SCSI interface is
the
direct electrical interface between
the
SCSI channel
and
the
drive
electronics.
It
handles all SCSI timing and protocol, and
transfer
of commands,
status
and
configuration information.
The
SCSI interface handles SCSI protocol without intervention from
the
microprocessor,
and is capable of automatically controlling
the
proper sequence of bus phases involved in
each transaction. Full arbitration and disconnectJreselection are implemented by
the
SCSI
interface.
RAM Buffer
The
RAM buffer contains 256-kilobytes of
static
RAM. All
data
transferred between
the
host
and
the
disk must pass through
the
RAM buffer.
Disk Controller
The
disk controller coordinates
the
flow
of
data
by interleaving RAM accesses between
the
SCSI interface and
the
disk controller.
It
contains a DMA section which controls
the
transfer
of
data
between
the
SCSI interface,
the
buffer RAM
and
the
disk controller.
The
DMA
accesses
the
256-kilobyte
static
RAM buffer
to
match
the
transfer speeds of
the
SCSI interface
and
the
disk controller.
The
disk controller also performs error checking on
data
being transferred from
the
disk
to
the
RAM buffer and generates ECC on
data
transferred from
the
RAM buffer
to
the
disk.
The
data
controller also does header verification during
read/write
operations.
Data Encoder/Decoder
The
primary
function of
the
Data
Encoder/Decoder is
to
convert between
the
NRZ (Non
Return
to
Zero)
datal
clock present on
the
SCSI channel and RLL (Run Length Limited,
1,7)
data
transferred
to
and from
the
disk surface. This includes sector length
and
content
information provided by
the
host during format operations as well as
data
transfers during
normal Read and Write operations.
Microcontroller
The
microcontroller used on
the
drive electronics/controller
PCA
is a single-chip device.
The
micro controller is responsible for decoding incoming SCSI commands, controlling
the
servo
processor
and
the
read/write
circuitry, and managing
the
head alignment function.
3·8
Product
Features
DRAFT
1/18/93
09:58
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