Intel 80C186XL, 80C188XL user manual Displacement

OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE

Displacement	High Address		Displacement
(Rate)	Age	Status	(Rate)
+	Rate		+
Base	Vac	Sick
			Base Register
Register	Dept	Div
	Employee
EA			EA
	Age	Status
	Rate
	Vac	Sick
	Dept	Div
	Employee
	Low Address
			A1019-0A

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.

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