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THE
80286
INSTRUCTION
SET
CMPS/CMPSB/CMPSW-Compare
string
operands
Opcode
A6
A6
A7
Instruction
.CMPS
mb,mb
CMPS8
CMPSW
FLAGS
MODIFIED
Clocks
8
8
8
Overflow, sign, zero, auxiliary carry, parity, carry
FLAGS
UNDEFINED
None
OPERATION
Description
Compare bytes ES:[DI] from [SI]
Compare bytes ES:[DI] from DS:[SI]
Compare
words
ES:[DI] from DS:[SI]
CMPS compares the byte or word pointed
to
by
SI with the byte or word pointed
to
by
OI
by
perform-
ing the subtraction
[SI] - [OI]. The result
is
not placed anywhere; only the flags reflect the result of
the subtraction. The types of the operands
to
CMPS determine whether bytes or words are compared.
The segment address ability of the first
(SI) operand determines whether a segment override byte
will
be produced or whether the default segment register DS
is
used. The second (DI) operand must be
addressible from the
ES register;
no
segment override
is
possible.
After the comparison
is
made, both SI and DI are automatically advanced.
If
the direction flag
is
0
(CLD
was
executed), the registers increment; if the direction flag
is
1 (STD
was
executed), the regis-
ters decrement. The registers increment or decrement
by
1 if a byte
was
moved;
by
2 if a word
was
moved.
CMPS can be preceded
by
the REPE or REPNE prefix for block comparison of CX bytes or words.
Refer to the REP instruction
for
details of this operation.
PROTECTED
MODE
EXCEPTIONS
#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
T ntf"rrl1,.,t 11
fnr
~
wnrn
()np.r~
nn
"t
()ff~p.t
OFFFFH.
---------r-
--
---
--
-----1.
8-34