User's Manual

THE 80286 INSTRUCTION SET
The rotate is repeated the number of times indicated by the second operand, which is either an immedi-
ate number
or the contents of the CL register. To reduce the maximum execution time, the 80286 does
not allow rotation counts greater than 31.
If a rotation count greater than 31 is attempted, only the
bottom
five bits of the rotation are used. The 8086 does not mask rotate counts.
The overflow flag is set only for the single-rotate (second operand = 1) forms of the instructions. The
OF bit is set to be accurate if a shift of length 1 is done. Since it is undefined for all other values,
including a zero shift, it can always
be set for the count-of-1 case regardless of the actual count. For
left shifts/rotates, the
CF bit after the shift is XORed with the high-order result bit. For right shifts/
rotates, the high-order
two bits of the result are XORed to get OF. Neither flag bit is modified when
the count value
is zero.
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 13 for a word operand at offset OFFFFH.
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