User's Manual

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