Technical Information
Microprocessor
The
803868X
is
a high-performancemicroprocessor
with
a
16-bit
external data path,
up to 16
megabytes
of
directly
addressable
physical memory
and
up to 64
terabytes
of
virtual memory
space.
The
operating
speed
of
the 803868X
chip
is
10MHz
in
Normal
mode
and
20MHz
in
Turbo
mode.
The
803868X operates
in
two
modes: protected
vir-
tual
address
mode
and
real
address
mode.
Protected
Virtual
Address
Mode
In
protected
mode,
softwarecan
perform
a task
switch
to
enter
virtual
8086 mode tasks.
Each
task behaves
with
8086 semantics, thus
allowing
8086 software
(an
application
program
or
an
entire
operation system)
to
execute.
The virtual
8086 tasks can be isolated and
protected
from
one another and the host 386SX
microprocessoroperation system
by
use
of
paging.
Protected
mode
will
use one
of
two different
address
spaces,
depending
on
whether
or not
paging
is
enabled.
Every
selector has a
logical
base address
of
up to 32 bits
in
length. This 32-bit logical
base address
is
added
to
the
effective
address
to form
a
final 32-bit
linear
address.
if
paging
is
disabled,
this final linear
address
reflects physical memory
and
is
truncated so
that
only
the
lower 24 bits of this
address are used
to
address the
16
megabyte
memory
address space.
If
paging
is
enabled
this final linear
address
reflects
a
32-bit
address.
This
is
translated
through
the
paging
unit to form
a 16-megabyte
physical
address.
32
j
)
)
Real
Address
Mode
Syst
in
real mode
the 3868X microprocessor operates
as
a
very fast 8086, but with
a
32-bit
extension
if
desired.
Real mode
is
required primarily to
set
up
the proces-
sor
for
protected
mode
operation.
The
segmentation
unit shifts
the selector
left
four bits
and adds the
result to
the
effective
address
to form
the
linear
address.
This linear
address
is_
limited to
1
megabyte.
In
addition, real
mode has
no
paging
capability.
em Timers
The
system has three programmable timer/counters
controlled by
the
Intel
8254-2 chip.
These are chan-
nels
0
through
2
defined
as
follows:
Channel
0
System
Timer
GATE
0
TlED ON
CLK
IN
0
1.190MHz
OSC
CLK
OUT
0
8259A lRO 0
Channel
1
Refresh
Request Generator
GATE
1
TlED ON
CLK
IN
1
1.190MHz
OSC
CLK
OUT
1
Request Refresh
Cycle
NOTE:
Channel
1
is
programmed
to
generate a
15
microsecond
signal.
Channel
2
Tone
Generation
for
Speaker
GATE 2
Controlled
by bit 0 of port hex
61
PP1 bit
CLK
IN
2
1.190MHz
OSC
CLK OUT 2
Used
to
drive speaker
33
Summary of Contents for Mini 80386SX
Page 1: ...o Mini 803863X 20MHz Mainboard User s Manual ...
Page 26: ......
