Filter
Top Products
THE
80286
INSTRUCTION SET
Following
is
a listing of the protected-mode checks and actions taken in the loading of a segment
register:
If
SS
is
loaded:
If
selector
is
null then #GP(O)
Selector
index must be within its descriptor table limits else
#GP
(selector)
Selector's RPL must equal CPL else
#GP
(selector)
AR
byte must indicate a writable data segment else
#GP
(selector)
DPL
in
the
AR
byte must equal CPL else
#GP
(selector)
Segment must be marked PRESENT else
#SS
(selector)
Load
SS
with selector
Load
SS
cache with descriptor
If
ES
or
DS
is loaded with non-null selector
Selector index must be within its descriptor table limits else
#GP
(selector)
AR
byte must indicate data
or
readable code segment else
#GP
(selector)
If data
or
non-conforming code, then both the RPL and the
CPL must be less than
or
equal to DPL in
AR
byte else
#GP
(selector)
Segment must
be
marked PRESENT else
#NP
(selector)
Load segment register with selector
Load segment register cache with descriptor
If
ES
or
DS
is
loaded with a null selector:
Load segment register with selector
Clear descriptor valid bit
PROTECTED MODE EXCEPTIONS
If
a segment register
is
being loaded, #GP, #SS, and #NP, as described in the listing above.
Otherwise,
#GP(O) if the destination
is
in
a non-writable segment.
#GP(O)
for an illegal memory operand
effective address
in
the CS, DS, or ES segments; #SS(O) for an illegal address in the
SS
segment.
REAL ADDRESS MODE EXCEPTIONS
Interrupt
13
for a word operand
at
offset OFFFFH.
8-74