Direct Addressing; Register Indirect Addressing; Based Addressing - Intel iAPX 86/88 User Manual

8086/8088 CPU
ENCODED
INTHE
INSTRUCTION
EXPLICIT {
INTHE
INSTRUCTION
ASSUMED
UNLESS
OVERRIDDEN
BY PREFIX
SINGLE INDEX
OR
DOUBLE INDEX
OR
EU
l
BIU
Figure 1-17 Memory Address Computation
r----,.----r---~-
-..,
I
OPCODE
I
MOD RIM
1
DISPLA CEM!N:
.-J
EA
Figure 1-18 Direct Addressing
II
OPCODE
I
MOD RIM
I
BX
I--g~-
I
OR
EA
SI
1--%7-
Figure 1-19 Register Indirect Addressing
I
1-19
e. Indexed Addressing
The effective address is calculated from the sum of a dis-
placement plus the content of an index register (SI or DI)
in index addressing (see Figure 1-22). Indexed address is
often used to access elements in an array (see Figure
1-23). The displacement locates the beginning of the ar-
ray, and the value of the index register selects one element
E~+i
I
EA
Figure 1-20 Based Addressing
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