MICROPROCESSOR TECHNOLOGY

Transcription

1 MICROPROCESSOR TECHNOLOGY Assis. Prof. Hossam El-Din Moustafa Lecture 6 Ch.3 Addressing Modes 1

2 Chapter Objectives Explain the operation of each data-addressing mode. Use data-addressing modes to form assembly language statements. Explain the operation of each program memoryaddressing mode. Use program memory-addressing modes to form assembly language statements. Select appropriate addressing modes 2

3 Data Addressing Modes 3

4 Data Addressing Modes The MOV instruction is a basis for the explanation of data-addressing modes. Example: MOV AX,BX Destination Source Opcode (operation Code): Tells the microprocessor which operation to perform. Operands: Source and destination are called operands 4

5 Data Addressing Modes Register addressing Immediate addressing Direct addressing Register indirect addressing Base-plus-index addressing Register relative addressing Base-relative-plus-index addressing Scaled index addressing 5

6 1. Register Addressing The most common form of data addressing. It uses 8, 16, 32 bit general purpose registers in addition to the six 16-bit segment registers. Registers must be of the same size. It does not affect the flag bits. A segment-to-segment register MOV is not allowed The Code segment register (CS) may not be the destination register. 6

7 1. Register Addressing (cont.) Example: MOV BX,CX Old contents of BX are overwritten. The contents of the destination register always change except when using CMP and TEST instructions. The above instruction does not affect the leftmost 16 bits of register EBX 7

8 1. Register Addressing (cont.) 8

9 2. Immediate Addressing The term immediate implies that the data immediately follow the hexadecimal opcode in memory. Immediate data are constant data, while the data transferred from a register are variable data. Hexadecimal data: MOV AX,44H & MOV AX,0F2H Decimal data: MOV CH, 100 ASCII data: MOV AL, A 9

10 2. Immediate Addressing (Cont.) ASCII data: MOV AL, AB (copies an ASCII BA) Binary data: MOV CL, B Example: 0100 B Offset Machine language MOV AX, 0 Opcode operands ;place 0000H into AX Comment form 10

11 2. Immediate Addressing (Cont.) B MOV EAX,13456H 11

12 3. Direct Data Addressing There are two types: A. Direct addressing: Applies to a MOV between a memory location and AL, AX, or EAX B. Displacement addressing: Applies to almost any instruction in the instruction set. 12

13 3. Direct Data Addressing (cont.) A. Direct Addressing: MOV AL,[1234H] DS=1000H Transfer a copy of the byte-sized contents of memory location 11234H into AL Intel make them 3-byte long (often appear) 13

14 3. Direct Data Addressing (cont.) 14

15 3. Direct Data Addressing (cont.) B. Displacement Addressing: Four or more bytes long. In P4, it reaches 7 bytes wide if we have 32 bit register and 32 bit displacement. MOV AL, DS: [1234H] MOV CL, DS:[1234H] Question 1: Compare between the above instructions Question 2: Compare with MOV AL, [1234H] 15

16 3. Direct Data Addressing (cont.) 16

17 Tdelay C gate * Vdd I DS 4. Register Indirect Addressing It transfers a byte or word between a register and a memory location addressed by an index or base register BP, BX, DI, or SI. It allows a program to refer to tabular data located in the memory system. MOV AX, [BX] Register BX contains 1000H Copy the word-sized data from the data segment offset address indexed by BX into AX. DS=0100H 17

18 4. Register Indirect Addressing (cont.) 18

19 4. Register Indirect Addressing (cont.) 19

20 5. Base-Plus-Index Addressing Similar to indirect addressing In 8086 to 80286, it uses one base register (BP or BX), and one index register (DI or SI) to indirectly access memory. The base register holds the beginning location of a memory array. The index register holds the relative position of an element in the array. In the and above, it allows the combination of any two 32-bit extended registers except ESP 20

21 5. Base-Plus-Index Addressing (cont.) MOV DX,[BX+DI) or MOV DX,[BX][DI] DS=0100H 21

22 5. Base-Plus-Index Addressing (cont.) 22

23 Thank You With all best wishes!! 23