-
8086 memory addressing modes provide flexible access to memory,
allowing you to easily access variables, arrays, records, pointers,
and other complex data types.
-12
addressing modes classified in 5 groups
i
) Addressing modes for register and immediate data
1.
Register addressing
-the
instruction will specify the name of the register which holds the
data to be
operated by the instruction
-ex:
MOV CL, DH : content of 8-bit DH register is moved to another
8-bit register CL
2.
Immediate addressing
-an
8-bit or 16-bit data is specified as a part of the instruction
-ex:
MOV DL, 08H : The 8-bit data (08H) given in the instruction is
moved to DL register
ii)
Addressing modes for memory data
3.
Direct addressing
-an
unsigned 16-bit displacement or signed 8-bit displacement will be
specified in the instruction
-ex:
MOV DX, [08H]
EA=0008H
(sign extended 8-bit displacement)
BA=
(DS)*16; MA=BA+EA
(DX)<=
(MA) OR DL<= (MA)
DH<=
(MA+1)
4.
Register indirect addressing
-the
name of the register which holds the effective address will be
specified in the instruction
-ex:
MOV CX, [BX]
5.
Based addressing
-BX
or BP register is used to hold a base value for effective address and
a signed 8-bit or unsigned 16-bit displacement will be specified in
the instruction
-ex:
MOV AX, [BX+08H]
6.
Indexed addressing
-SI
or DI reg. is used to hold an index value for memory data and a
signed 8-bit displacement or unsigned 16-bit displacement will be
specified in the instruction
-ex:
MOV CX,[SI+0A2H]
7.
Based index addressing
-the
EA is given by the sum of base value and 8-bit or 16-bit displacement
specified in the instruction
-ex:
MOV DX,[BX+SI+0AH]
8.
String addressing
-for
string instructions
-EA
of source data is stored in SI reg. and the EA of destination data is
stored in DI reg.
iii)
Addressing modes for I/O ports
9.
Direct I/O port addressing
-used
to access data from standard I/O mapped devices or ports.
-ex:
IN AL, [09H]: the content of port with address 09H is moved to AL
10.
Indirect I/O port addressing
-is
used to access data from standard I/O mapped devices or ports and the
instruction will specify the name of the register which holds the
port address.
-ex:
OUT [DX], AX : the content of AX is moved to port whose address is
specified by DX
iv)
Relative addressing modes
11.
Relative addressing
-EA
of the pgm instruction is specified relative to IP by an 8-bit
displacement
-ex:
JZ 0AH
v)
Implied addressing modes
12.
Implied addressing
-in
this the instruction itself will specify the data to be operated by
the instruction
-ex:
CLC: clear carry
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