Intel and compatable CPU's Programming Information
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LTR -- Load Task Register
Opcode Instruction Clocks Description 0F 00 /3 LTR r/m16 pm=23/27 Load EA word into task register
DescriptionLTR 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.
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 ExceptionsInterrupt 6; LTR is not recognized in Real Address Mode
Virtual 8086 Mode ExceptionsSame exceptions as in Real Address Mode
NotesThe operand-size attribute has no effect on this instruction.