Intel 80C186EA, User Manual

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INSTRUCTION SET DESCRIPTIONS
C-10
CMP Compare:
CMP dest, src
Subtracts the source from the desti-
nation, which may be bytes or words,
but does not return the result. The
operands are unchanged, but the flags
are updated and can be tested by a
subsequent conditional jump
instruction. The comparison reflected
in the flags is that of the destination to
the source. If a CMP instruction is
followed by a JG (jump if greater)
instruction, for example, the jump is
taken if the destination operand is
greater than the source operand.
Instruction Operands:
CMP reg, reg
CMP reg, mem
CMP mem, reg
CMP reg, immed
CMP mem, immed
CMP accum, immed
(dest) – (src) AF
ü
CF
ü
DF –
IF –
OF
ü
PF
ü
SF
ü
TF –
ZF
ü
CMPS Compare String:
CMPS dest-string, src-string
Subtracts the destination byte or word
from the source byte or word. The
destination byte or word is addressed
by the destination index (DI) register
and the source byte or word is
addresses by the source index (SI)
register. CMPS updates the flags to
reflect the relationship of the
destination element to the source
element but does not alter either
operand and updates SI and DI to
point to the next string element.
Instruction Operands:
CMP dest-string, src-string
CMP (repeat) dest-string, src-string
(dest-string) – (src-string)
if
(DF) = 0
then
(SI)
←
(SI) + DELTA
(DI)
←
(DI) + DELTA
else
(SI)
←
(SI) – DELTA
(DI)
←
(DI) – DELTA
AF
ü
CF
ü
DF –
IF –
OF
ü
PF
ü
SF
ü
TF –
ZF
ü
Table C-4. Instruction Set (Continued)
Name Description Operation
Flags
Affected
NOTE: The three symbols used in the Flags Affected column are defined as follows:
– the contents of the flag remain unchanged after the instruction is executed
? the contents of the flag is undefined after the instruction is executed
ü
the flag is updated after the instruction is executed