User's Manual

THE 80286 INSTRUCTION SET
DEC-Decrement by 1
Opcode
FE /1
FF /1
48+ rw
FLAGS MODIFIED
I!'structlon
DEC eb
DEC ew
DEC rw
Clocks
2,mem=7
2,mem=7
2
Overflow, sign, zero, auxiliary carry, parity
FLAGS UNDEFINED
None
OPERATION
Description
Decrement EA byte by 1
Decrement
EA word by 1
Decrement word register by 1
1 is subtracted from the operand. Note that the carry flag is not changed by this instruction. If you
want the carry flag set, use the SUB instruction with a second operand of 1.
PROTECTED MODE EXCEPTIONS
#GP(O) if the operand 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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