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2.4.3.3

MEMORY MODE

80286

BASE ARCHITECTURE

MODULE A

MODULE B

PROCESS

STACK

PROCESS

DATA

BLOCK 1

r---...,

I I

~

ODE

DATA

CODE

DATA

I

I

I I

I I

I I

[l

PRog~~~D

BLOCK 2

I I

L

___

.J

MEMORY

CPU

L

I-

CODE

DATA

STACK

-

I-

EXTRA

SEGMENT

REGISTERS

Figure 2-12. Use of Memory Segmentation

Two modes are

!.!sed

for

simple

scalar operands located

in

memory:

G301uo

Direct Address Mode. The offset of the operand

is

contained

in

the instruction

as

the displacement

element. The offset

is

a 16-bit quantity.

Register Indirect Mode. The offset of the operand

is

in one of the registers SI, DI, or

BX.

(BP

is

excluded; if BP

is

used

as

a stack frame base, it requires an index

or

displacement component to

reference either parameters passed

on

the stack or temporary variables allocated

on

the stack. The

instruction level bit encoding for the BP only address mode

is

used to specify Direct Address

mode. See Chapter

12

for more details.)

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