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Ia
r I
!larI1:
rep
i
80286
SYSTEM INITIALIZATION
Form an
adlij!lmenl
faclor
from
Ihe
r~al
CS
bale
of
FFOOOOH
10
Ihe
!egmenl
bale
address
assumed
by
ASM286
•.
Any
data
reference
made
Inlo
CS
mij!1
add
an
Indexing
lerm
IBPI
10
compen!ale
for
Ihe
difference
belween
Ihe
off!el
genera
led
by
ASM286
and
Ihe
off!el
reqijlred
from
Ihe
bale
of
FFOOOOH.
proc
c a
II
!larl1
pop
bp
!ijb
bp,offul
!larl1
II
d t
I n I I I a
I_g
d I I
bpi
The
valije
of
IP
al
rijn
lime
will
nol
be
Ihe
lame
a!
Ihe
one
ij!ed
by
ASM286!
Get
Irije
off!el
of
!lart1
Sijblracl
ASM286
offset
of
!lart1
leaving
adlij!lment
faclor
In
BP
Setijp
nijll
IDT
10
force
shij1down
on
any
protecllon
error
or
Inlerrijpt
Copy
the
EPROM-ba!ed
lemporary
GDT
Inlo
RAM.
lea
mov
maY!
!I,lnlllal_gdllbpl
;
Selijp
polnler
10
lemporary
GDT
templale
In
EPROM
c x , ( e n d_g d I - I n
III
a
I_g
d I ) I 2 5 e I
len
g I h
es:word
plr
Idll,cs:lslli
Pijl
Inlo
reserved
RAM
area
Look
for
80287
processor
exten!lon.
A!sijme
all
one!
will.
be
read
If
an
80287
15
nol
pre!enl.
f n I n I I
Inillalize
80287
If
preunt
mov
bx,EM
A!!ume
no
80287
htsw
ax
Look
al
!lah!
of
80287
or
a
I,
a I
Ho
error.
!hould
be
pre!enl
In
z
!el_mode
Jump
If
no
80287
hetpm
Put
80287
In
t 0
protecled
mode
mov
bx,MP
Swllch
to
prolecled
mode
and
!elup
a
stack,
GDT,
and
LDT.
!el_mode:
!m!w
or
ax
..
,PE
ax,bx
ax
Get
current
MSW
Sel
PE
bit
or
Im!w
Imp
i
.2
A-4
Sel
HPX
!lalu!
flag!
Enter
prolected
mode!
Clear
qijeij~
of
In,lr"ctlon~
decoded
while
In
Real
Addre!s
Mode
CPL
15
now
0,
CS
!IIII
polnl!
at
FFFE10
In
phy!lcal
memory