3-671
INSTRUCTION SET REFERENCE
STR—Store Task Register
Description
This instruction stores the segment selector from the task register (TR) in the destination
operand. The destination operand can be a general-purpose register or a memory location. The
segment selector stored with this instruction points to the task state segment (TSS) for the
currently running task.
When the destination operand is a 32-bit register, the 16-bit segment selector is copied into the
lower 16 bits of the register and the upper 16 bits of the register are cleared to 0s. When the desti-
nation operand is a memory location, the segment selector is written to memory as a 16-bit
quantity, regardless of operand size.
The STR instruction is useful only in operating-system software. It can only be executed in
protected mode.
Operation
DEST
<
TR(SegmentSelector);
Flags Affected
None.
Protected Mode Exceptions
#GP(0)
If the destination is a memory operand that is located in a nonwritable
segment or if the effective address is outside the CS, DS, ES, FS, or GS
segment limit.
If the DS, ES, FS, or GS register is used to access memory and it contains
a null segment selector.
#SS(0)
If a memory operand effective address is outside the SS segment limit.
#PF(fault-code)If a page fault occurs.
#AC(0)
If alignment checking is enabled and an unaligned memory reference is
made while the current privilege level is 3.
Opcode
Instruction
Description
0F 00 /1
STR r/m16
Stores segment selector from TR in r/m16
