Specifications
4.6.7
Floppy
Disk
Controll
..
A 37C65B floppy disk subsystem controller provides the equivalent
of
an
entire
PC
compati-
ble floppy disk controller plug-in card, within a single LSI device.
This
"superchip" integrates:
• Formatter/controller
• Digital
data
separation
• Digital write precompensation
•
Data
rate selection
• Clock generation
• Drive interface drivers and receivers
• Drive motor control
•
PC
(and
AT)
compatible coptrol registers
The 37C65B
and
associated intemallogic are completely compatible with the industry stand-
ard NEC765 floppy controller, and associated external devices, as implemented
in
a standard
PC.
The
37C65B floppy controller offers data rates
of
125,
250, 300,
and
SOOK
bits/second.
However, the board's ROM-BIOS does not support the 300K bits/second option,
and
a
crys-
tal must be added
in
a specified position
on
the
board
to allow use
of
that data rate.
The 37C65B's internal
data
separator contains a highly reliable all-digital 2nd order, "type
2"
phase locked loop.
Its
internal
high
current
drive
outputs
can
sink
up
to
48 mA
current
on
the floppy disk drive interface. Write precompensation is also generated within the 37C65B,
with a choice
of
two values,
125
oS
and 187
oS,
set via a jumper
on
the board.
The
board's
ROM-BIOS
reads
four bits
of
floppy subsystem configuration
data
through
a
read-only input port, located
at
I/O
address 338h. These bits are used
to
determine the type
of
floppy drives installed as drives A and B (four choices for each drive).
The
remaining four
bits
of
this 8-bit input are used for other purposes (serial handshake input
and
SCSI
10).
The
four floppy type bits reflect the state
of
four jumpers
on
the board, W'1fj-W29. They appear
in
bits
4-6
of
the
input
I/O
port. When a jumper is on, the corresponding bit will
be
read
as a
0;
when
a
jumper
is off,
the
bit
will
be
read
as a logic 1.
If
no
floppy subsystem is
used
(onboard
or
off),
the
four floppy type bits, as programmed
by
their respective jumpers, are
available for other purposes.
4.6.8
SCSI
Bus
Interface
A Small
Computer
System Interface replaces
the
hard
disk controller
normally
found
in
a
standard "XT" computer. The SCSI bus interface is completely controlled by a
53C8O
SCSI
protocol controller device. The
53C8O
provides
an
interface which meets
the
ANSI X3.131
specification for SCSI, includIDg Initiator role, Target role, Arbitration,
and
the
Disconnect-
Reselect function. The
Ampro
SCSIIBIOS automatically maps ROM-BIOS
hard
disk relat-
ed
functions
to
this interface, usmg the SCSI direct access device "Common Command Set"
for compatibility with a wide variety
of
SCSI disk drives.
The
53C80 SCSI
controller
contains eight
internal
read/write
ports
(beginnipg
at
330h),
allows full programmable control
of
17 bidirectional bus signals,
and
provides
both
buffered
(low
leakage)
bus. inputs
and
high
current
(48 mA)
bus
output
drive capacity.
Chapter
5
provides a list
of
the internal registers and their
I/O
port addresses as implemented
on
the
Little
Board/PC.
Please refer 'to the 53C80 technical manual referenced earlier
in
this chap-
ter
for complete technical and functional information
on
the 53C80. .
4-13