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Chapter 17 -- 80386 Instruction Set
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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
Description
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
None
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
Notes
The operand-size attribute has no effect on this instruction.
up:
Chapter 17 -- 80386 Instruction Set
prev: LSL Load Segment Limit
next: MOV Move Data