User's Manual
THE
80286
INSTRUCTION SET
IMUL-Signed
Multiply
Opcode
Instruction Clocks
F6
15
IMUL eb
13,mem=~6
F7
15
IMUL ew 21,mem=24
68
Ir
db
IMUL rw,db 21,mem=24
69
Ir
dw
IMUL rw,ew,dw 21,mem=24
68
Ir
db
IMUL rw,ew,db 21,mem=24
FLAGS
MODIFIED
Overflow, carry
FLAGS
UNDEFINED
Sign, zero, auxiliary carry, parity
OPERATION
Description
Signed multiply
(AX
= AL X
EA
byte)
Signed multiply
(DXAX
=
AX
X
EA
word)
Signed multiply
imm.
byte into word reg.
Signed multiply (rw =
EA
word X
imm.
word)
Signed multiply (rw =
EA
word X
imm.
byte)
IMUL
performs signed multiplication.
If
IMUL
has a single byte source operand, then the source
is
multiplied by AL and the 16-bit signed result
is
left
in
AX. Carry and overflow are set to 0 if AH
is
a
sign extension of AL; they are set to 1 otherwise.
If
IMUL
has a single word source operand, then
the
source operand
is
multiplied. by AX and the
32-bit signed result
is
left
in
DX:AX. DX contains the high-order
16
bits of the product. Carry and
overflow are set to
0 if DX
is
a sign extension of AX; they are set to 1 otherwise.
If
IMUL
has three operands, then the second operand (an effective address word)
is
multiplied by the
third operand (an immediate word), and the
16
bits of the result are placed
in
the first operand (a
word register). Carry and overflow are set to
0 if the result fits in a signed word (between - 32768 and
+32767, inclusive); they are set to 1 otherwise.
NOTE
The
low
16
bits of the product of a 16-bit signed multiply are the same
as
those
of
an unsigned
mUltiply. The three operand
IMUL
instruction can be used for unsigned operands as
well.
PROTECTED MODE EXCEPTIONS
#GP(O) for an illegal memory operand effective address
in
the CS, DS,
or
ES segments;
#SS(O)
for an
~11~
__
1
__
.l..J
__
~~!_
"-1..
.....
C'C'
....
"""'"
........
""
.....
+
11111;:;5a1
a.UUl
\.<,:),:)
~11
LU
......
UIJ
.,
.....
OJ.J.J.
.....
u.
...
REAL ADDRESS MODE EXCEPTIONS
Interrupt
13
for a word operand at offset OFFFFH.
8-44