80386 Programmer's Reference Manual -- Opcode LTR

LTR -- Load Task Register

OpcodeInstructionClocks DescriptionExample
0F 00 /3ltrw r/m16pm=23/27 Load EA word into task registerltrw %cx
ltrw (%ebx,1)
ltrw (%ebx,2)
ltrw (%ebx,%ebp,1)


LTR loads the task register from the source register or memory location specified by the operand. The loaded task state segment is marked busy. A task switch does not occur.

LTR is used only in operating system software; it is not used in application programs.

Flags Affected


Protected Mode Exceptions

#GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #GP(0) if the current privilege level is not 0; #GP(selector) if the object named by the source selector is not a TSS or is already busy; #NP(selector) if the TSS is marked "not present"; #PF(fault-code) for a page fault

Real Address Mode Exceptions

Interrupt 6; LTR is not recognized in Real Address Mode

Virtual 8086 Mode Exceptions

Same exceptions as in Real Address Mode


The operand-size attribute has no effect on this instruction.

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