User's Manual

THE 80286 INSTRUCTION SET
CMP-Compare Two Operands
Opcode
Instruction Clocks
3C db
CMP AL,db
3
3D dw
CMP AX,dw
3
80
17
db
CMP eb,db
3,mem=6
38
Ir
CMP eb,rb 2,mem=7
83
17
db
CMP eW,db
3,mem=6
81
17
dw
CMP eW,dw 3,mem=6
39
Ir
CMP eW,rw 2,mem=7
3A
Ir
CMP rb,eb 2,mem=6
38
Ir
CMP rW,ew 2,mem=6
FLAGS MODIFIED
Overflow, sign, zero, auxiliary carry, parity, carry
FLAGS UNDEFINED
None
OPERATION
Description
Compare immediate byte from AL
Compare immediate word from
AX
Compare immediate byte from EA byte
Compare byte register from
EA byte
Compare immediate byte from EA word
Compare immediate word from
EA word
Compare word register from
EA word
Compare
EA byte from byte register
Compare
EA word from word regisler
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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