User's Manual

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.
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