Intel 80C186XL, User Manual

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C-17
INSTRUCTION SET DESCRIPTIONS
IMUL Integer Multiply:
IMUL src
Performs a signed multiplication of the
source operand and the accumulator.
If the source is a byte, then it is
multiplied by register AL, and the
double-length result is returned in AH
and AL. If the source is a word, then it
is multiplied by register AX, and the
double-length result is returned in
registers DX and AX. If the upper half
of the result (AH for byte source, DX
for word source) is not the sign
extension of the lower half of the
result, CF and OF are set; otherwise
they are cleared. When CF and OF are
set, they indicate that AH or DX
contains significant digits of the result.
Instruction Operands:
IMUL reg
IMUL mem
IMUL immed
When Source Operand is a Byte:
(AX)
←
(byte-src) × (AL)
if
(AH) = sign-extension of (AL)
then
(CF)
←
0
else
(CF)
←
1
(OF)
←
(CF)
When Source Operand is a Word:
(DX:AX)
←
(word-src) × (AX)
if
(DX) = sign-extension of (AX)
then
(CF)
←
0
else
(CF)
←
1
(OF)
←
(CF)
AF ?
CF
ü
DF –
IF –
OF
ü
PF ?
SF ?
TF –
ZF ?
IN Input Byte or Word:
IN accum, port
Transfers a byte or a word from an
input port to the AL register or the AX
register, respectively. The port number
may be specified either with an
immediate byte constant, allowing
access to ports numbered 0 through
255, or with a number previously
placed in the DX register, allowing
variable access (by changing the value
in DX) to ports numbered from 0
through 65,535.
Instruction Operands:
IN AL, immed8
IN AX, DX
When Source Operand is a Byte:
(AL)
←
(port)
When Source Operand is a Word:
(AX)
←
(port)
AF –
CF –
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
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