User's Manual

THE 80286 INSTRUCTION SET
ARPL - Adjust RPL Field of Selector
Opcode
Instruction
63 Ir
ARPL ew,rw
FLAGS MODIFIED
Zero
FLAGS UNDEFINED
None
OPERATION
Clocks.
10,mem=11
Description
Adjust RPL of EA word not less than RPL of
rw
The ARPL instruction has two operands. The first operand is a 16-bit memory variable or word register
that contains the value of a
selector. The second operand is a word register. If the RPL field (bottom
two bits) of the first operand
is less than the RPL field of the second operand, then the zero flag is set
to 1 and the RPL field of the first operand is increased to match the second RPL. Otherwise, the zero
flag
is set to 0 and no change is made to the first operand.
ARPL appears in operating systems software, not in applications programs. It is used to guarantee that
a selector parameter to a subroutine does not request more privilege than the caller
was entitled to.
The second operand used by ARPL would normally be a register that contains the CS selector value
of the caller.
PROTECTED MODE EXCEPTIONS
#GP(O) if the result is in a non-writable segment. #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. ARPL is not recognized in Real Address mode.
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