Accessing A Structure With Based Addressing - Intel 80C186XL User Manual

OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE
Displacement
(Rate)
+
Base
Register
EA
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.
2-32
High Address
Age Status
Rate
Vac Sick
Dept Div
Employee
Age Status
Rate
Vac Sick
Dept Div
Employee
Low Address
Displacement
(Rate)
+
Base Register
EA
A1019-0A