Base-plus-index addressing is similar to indirect addressing because it indirectly addresses memory data. In the 8086 through the 80286, this type of addressing uses one base register (BP or BX) and one index register (DI or SI) to indirectly address memory. The base register often holds the beginning location of a memory array, whereas the index register holds the relative position of an element in the array. Remember that whenever BP addresses memory data, both the stack segment register and BP generate the effective address.
In the 80386 and above, this type of addressing allows the combination of any two 32-bit extended registers except ESP. For example, the MOV DL,[ ] instruction is an example using EAX (as the base) plus EBX (as the index). If the EBP register is used, the data are located in the stack segment instead of in the data segment.
Locating Data with Base-Plus-Index Addressing. Figure 3–8 shows how data are addressed by the MOV DX,[ ] instruction when the microprocessor operates in the real mode. In this example, , which translate into memory address 02010H. This instruction transfers a copy of the word from location 02010H into the DX register. Lists some instructions used for base-plus-index addressing. Note that the Intel assembler requires that this addressing mode appear as [BX][DI] instead of [ ]. The MOV DX,[ ] instruction is MOV DX,[BX][DI] for a program written for the Intel ASM assembler. This…
