Intel 80287, 80286 manual Inter

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THE 80286 INSTRUCTION SET

If ES or OS is loaded with non-null selector:

AR byte must indicate data or readable code segment else #GP (selector) If data or non-conforming code, then both the RPL and the

CPL must be less than or equal to OPL in AR byte else #GP (selector) Segment must be marked PRESENT else #NP (selector)

Load segment register with selector

Load segment register cache with descriptor If ES or OS is loaded with a null selector:

Load segment register with selector Clear valid bit in cache

PROTECTED MODE EXCEPTIONS

If a segment register is being loaded, #GP, #SS, and #NP, as described in the listing above.

Otherwise, #SS(O) if the current top of stack is not within the stack segment.

#GP(O) if the destination 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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