Intel 80286, 80287 manual SUB-Integer Subtraction

THE 80286 INSTRUCTION SET

SUB-Integer Subtraction

Opcode			Instruction		Clocks	Description
28	Ir		SUB	eb,rb	2,mem=7	Subtract byte register from EA byte
29	Ir		SUB	eW,rw	2,mem=7	Subtract word register from EA word
2A	Ir		SUB	rb,eb	2,mem=7	Subtract EA byte from byte register
2B	Ir		SUB	rW,ew	2,mem=7	Subtract EA word from word register
2C	db		SUB	AL,db	3	Subtract immediate byte from AL
20	dw		SUB	AX,dw	3	Subtract immediate word from AX
80	15	db	SUB	eb,db	3,mem=7	Subtract immediate byte from EA byte
81	15	dw	SUB	eW,dw	3,mem=7	Subtract immediate word from EA word
83	15	db	SUB	eW,db	3,mem=7	Subtract immediate byte from EA word

FLAGS MODIFIED

Overflow, sign, zero, auxiliary carry, parity, carry

FLAGS UNDEFINED

None

OPERATION

The second operand is subtracted from the first operand, and the first operand is replaced with the result.

When a byte-immediate value is subtracted from a word operand, the immediate value is first sign-extended.

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.

B-109