Intel 80286, 80287 manual CMP-Compare Two Operands, Cmp

THE 80286 INSTRUCTION SET

CMP-Compare Two Operands

Opcode			Instruction		Clocks	Description
3C	db		CMP AL,db		3	Compare immediate byte from AL
3D	dw		CMP AX,dw		3	Compare immediate word from AX
80	17	db	CMP	eb,db	3,mem=6	Compare immediate byte from EA byte
38	Ir		CMP	eb,rb	2,mem=7	Compare byte register from EA byte
83	17	db	CMP eW,db		3,mem=6	Compare immediate byte from EA word
81	17	dw	CMP eW,dw		3,mem=6	Compare immediate word from EA word
39	Ir		CMP eW,rw		2,mem=7	Compare word register from EA word
3A	Ir		CMP rb,eb		2,mem=6	Compare EA byte from byte register
38	Ir		CMP rW,ew		2,mem=6	Compare EA word from word regisler

FLAGS MODIFIED

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

FLAGS UNDEFINED

None

OPERATION

CMP subtracts the second operand from the first operand, but it does not place the result anywhere. Only the flags are changed by this instruction. CMP is usually followed by a conditional jump instruc- tion. See the "]cond" instructions in this chapter for the list of signed and unsigned flag tests provided

by the 80286. '.

If a word operand is compared to an immediate byte value, the byte value is first sign-extended.

PROTECTED MODE EXCEPTIONS

#GP(O) for an illegal memory operand effective address in the CS, DS, or ES segments; #8S(0) 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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