User's Manual

THE 80286 INSTRUCTION SET
LLDT -Load Local Descriptor Table Register
Opcode Instruction
OF 00 /2
LLDT ew
FLAGS MODIFIED
None
FLAGS UNDEFINED
None
OPERATION
Clocks
17,mem=19
Description
Load selector ew into Local Descriptor Table
register
The word operand (memory or register) to LLDT should contain a selector pointing to the Global
Descriptor Table. The GDT entry should be a Local Descriptor Table Descriptor.
If so, then the Local
Descriptor Table Register
is loaded from the entry. The descriptor cache entries for DS, ES, SS, and
CS are not affected. The LDT field in the TSS is not changed.
The selector operand.is allowed
to be zero. In that case, the Local Descriptor Table Register is marked
invalid. All descriptor references (except by LAR, VERR, VERW or
LSL instructions) will cause a
#GP fault.
LLDT appears in operating systems software;
it does not appear in applications programs.
PROTECTED MODE EXCEPTIONS
#GP(O) if the current privilege level is not O. #GP (selector) if the selector operand does not point into
the Global Descriptor Table, or if the entry in the GDT
is not a Local Descriptor Table. #NP (selector)
if LDT descriptor
is not present. #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 6; LLDT is not recognized in Real Address Mode.
B-66