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THE
80286
INSTRUCTION SET
LGDT
ILIDT
-Load
Global/Interrupt
Descriptor Table Register
Opcode
OF
01
/2
OF
01
/3
FLAGS MODIFIED
None
Instruction
LGDT m
LlDT m
FLAGS UNDEFINED
None
OPERATION
Clocks
11
12
Description
Load m into Global Descriptor Table reg
Load
m into Interrupt Descriptor Table reg
The Global or the Interrupt Descriptor Table Register
is
loaded from the
six
bytes of memory pointed
to by the effective address operand (see figure 10.3). The LIMIT field of the descriptor table register
loads from the first word; the next three bytes
go
to the BASE field of the register; the last byte
is
ignored.
LGDT and LIDT appear
in
operating systems software; they are not used
in
application programs.
These are the only instructions that directly load a physical memory address
in
80286 protected mode.
PROTECTED MODE EXCEPTIONS
#GP(O)
if the current privilege level
is
not
O.
#UD if source operand
is
a register.
#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
These instructions are valid
in
Real Address mode
to
allow the power-up initialization
for
Protected
mode.
Interrupt
13
for a word operand at offset OFFFFH. #UD if source operand
is
a register.
8-65