Intel 80287, 80286 manual LLDT-Load Local Descriptor Table Register, Lldt ew

THE 80286 INSTRUCTION SET

LLDT-Load Local Descriptor Table Register

Opcode	Instruction	Clocks	Description
OF 00 /2	LLDT ew	17,mem=19	Load selector ew into Local Descriptor Table
			register

FLAGS MODIFIED

None

FLAGS UNDEFINED

None

OPERATION

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