Filter
Top Products
80386
3.3 RESERVED LOCATIONS
There are two fixed areas
in
memory which are re-
served
in
Real address mode: system initialization
area and the interrupt table area. Locations
OOOOOH
through 003FFH are reserved for interrupt vectors.
Each one of the 256
possible interrupts has a 4-byte
jump vector reserved for
it.
Locations FFFFFFFOH
through FFFFFFFFH are reserved for system
initiali-
zation.
3.4 INTIERRUPTS
Many of the exceptions shown in Table 2-5 and dis-
cussed
in
section 2.9 are not applicable to Real
Mode operation,
in
particular exceptions 10,
11,
14,
will not happen
in
Real Mode. Other exceptions
have
slightly different meanings
in
Real Mode; Table
3-1
identifies these exceptions.
3.5 SHUTDOWN AND HALT
The HL T instruction stops program execution and
prevents the processor from using the
local bus until
restarted. Either
NMI, INTR with interrupts enabled
(IF
= 1), or RESET will force the 80386 out of halt.
If
interrupted, the saved CS:IP will point to the next
instruction after the HL
T.
Shutdown will occur when a severe error is detected
that prevents further processing.
In
Real Mode,
shutdown can occur under two conditions:
An interrupt or
an
exception occur (Exceptions 8
or
13)
and the interrupt vector
is
larger than the
Interrupt Descriptor Table
(i.e.
There
is
not
an
in-
terrupt
handler for the interrupt).
A CALL,
INT or
PUSH
instruction attempts to wrap
around the stack segment when
SP
is
not even.
(e.g.
pushing a value
on
the stack when
SP
=
0001
resulting
in
a stack segment greater than
FFFFH)
An
NMI
input can bring the processor out of shut-
down if the
Interrupt Descriptor Table limit
is
large
enough to contain the NMI interrupt vector (at least
0017H)
and
the stack has enough room to contain
the vector and
flag information
(i.e.
SP
is
greater
than
0005H). Otherwise shutdown can only be exit-
ed
via the RESET input.
4.
PROTIECTIED
MODIE
ARCHITIECTURE
4.1
INTRODUCTION
The complete capabilities of the 80386 are unlocked
when the processor operates
in
Protected Virtual
Address Mode (Protected Mode). Protected Mode
vastly increases the linear address space to four gig-
abytes
(2
32
bytes) and allows the running of virtual
memory programs of almost unlimited size (64 tera-
bytes or 2
46
bytes).
In
addition Protected Mode al-
lows
the 80386 to
run
all of the existing 8086 and
80286 software, while providing a sophisticated
memory management and a hardware-assisted pro-
tection mechanism.
Protected Mode allows the use
of
additional instructions especially optimized for
supporting
multitasking operating systems. The base
architecture of the
80386 remains the same, the reg-
isters, instructions, and addressing modes described
in
the previous sections are retained. The main dif-
ference between
Protected Mode, and Real Mode
from a programmer's view
is
the increased address
space, and a different addressing mechanism.
Table
3·1
Function
Interrupt
Related
Return
Number
Instructions Address Location
Interrupt table limit too small 8 INT Vector
is
not Before
within
table limit
Instruction
CS,
OS,
ES,
FF,
GS
13
Word memory reference
Before
Segment overrun exception
beyond offset
= FFFFH.
Instruction
An
attempt to execute
past the end of
CS
segment.
SS
Segment overrun exception
12
Stack Reference
Before
beyond offset
= FFFFH Instruction
33