Intel 80C186XL, User Manual

Page: 61 / 405

OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE
2-32
Figure 2-16. Accessing a Structure with Based Addressing
With indexed addressing, the effective address is calculated by summing a displacement and the
contents of an index register (SI or DI, see Figure 2-17). Indexed addressing is often used to ac-
cess elements in an array (see Figure 2-18). The displacement locates the beginning of the array,
and the value of the index register selects one element. If the index register contains 0000H, the
processor selects the first element. Since all array elements are the same length, simple arithmetic
on the register can select any element.
Displacement
(Rate)
EA
Displacement
(Rate)
Base Register
EA
Age
Status
Rate
Sick
Vac
Dept Div
Employee
High Address
Low Address
+
Base
Register
+
Age
Status
Rate
Sick Vac
Dept Div
Employee
A1019-0A