Addressing modes in computer architecture

ADDRESSING AND ADDRESSING MODES To perform any operation, the corresponding instruction is to be given to the microprocessor. In each instruction, programmer has to specify 3 things: · Operation to be performed. · Address of source of data. · Address of destination of result. Definition: · The different ways in which the location of an operand is specified in an instruction are referred to as addressing modes. · The method by which the address of source of data or the address of destination of result is given in the instruction is called Addressing Modes · Computers use addressing mode techniques for the purpose of accommodating one or both of the following provisions: · To give programming versatility to the user by providing such facilities as pointers to memory, counters for loop control, indexing of data, and program relocation. · To reduce the number of bits in the addressing field of the instruction. IMPLEMENTATION OF VARIABLES AND CONSTANTS Variables and constants are the simplest data types and are found in almost every computer program. A variable is represented by allocating a register or a memory location to hold its value. Thus, the value can be changed as needed using appropriate instructions. 1. Register addressing mode - The operand is the contents of a processor register; the name (address) of the register is given in the instruction. Example: MOVE R1,R2 This instruction copies the contents of register R2 to R1. 2. Absolute addressing mode - The operand is ...

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2. Indirect Addressing Mode: In Indirect addressing mode, the address field in the instruction contains the memory location or register where the effective address of the operand is present. It requires two memory access. It is further classified into two categories: Register Indirect, and Memory Indirect. Example: LOAD R1, @500 The above instruction is used to load the content of the memory location stored at memory location 500 to register R1. In other words, we can say, effective address is stored at memory location 500. Difference between Direct and Indirect Addressing Modes: Parameters Direct Addressing Mode Indirect Addressing Mode Address Field Address field contains the effective address of operand. Address field contains reference of effective address. Memory References Requires only one memory reference Requires two memory references Processing Speed This addressing mode has fast addressing compared to indirect addressing mode It is slower than direct addressing mode. Classification No further classification Further classified into two categories- Memory Indirect and Register Indirect Addressing Mode. Calculation No further calculation is required to perform the operation. Requires further calculation to find the effective address. Address Space It occupies a smaller amount of space than the indirect mode. It occupies a large amount of space than the direct mode. Overhead No additional overhead is involved while searching for operand. Additional overhead is invol...

Purpose of Addressing Modes in Computer Architecture Tutorial with Examples Addressing Modes Addressing modes are the ways how architectures specify the address of an operand of an instruction. There are various addressing modes Implied Mode In this mode the operands are specified implicitly in the definition of an instruction. Immediate Mode In this mode the operand is specified in the instruction itself or we can say that, an immediate mode instruction has an operand rather than an address. Register Mode In this mode, the operands are in registers. Direct Address Mode It this mode, the address of the memory location that holds the operand is included in the instruction. The effective address is the address part of the instruction. Indirect Address Mode In this mode the address field of the instruction gives the address where the effective address is stored in memory. Relative Address Mode In this mode the content of program counter is added to the address part of the instruction to calculate the effective address. Indexed Address Mode In this mode, the effective address will be calculated as the addition of the content of index register and the address part of the instruction. Data Transfer Instructions Data Transfer Instructions cause transfer of data from one location to another without changing the information content. The common transfers may be between memory and processor registers, between processor registers and input/output. Typical Data Transfer Instructions Na...

Indirect addressing involves specifying a memory address that contains the actual address of the operand. This can be useful when the actual address of the operand is not known at the time the instruction is executed. In indirect addressing, the address of the operand is obtained by accessing the memory location specified by the indirect address. For example, in the instruction “MOV AX, [BX]”, the memory location specified by the contents of the BX register is accessed to obtain the actual address of the operand. Implied addressing, on the other hand, involves not explicitly specifying an address for the operand, but instead relying on the instruction’s operation code (opcode) to implicitly determine the location of the operand. This is typically used when the operand is a register or a fixed memory location that is known in advance. For example, in the instruction “INC AX”, the operand is the AX register, which is implicitly specified by the opcode of the instruction. Both indirect and implied addressing modes are used extensively in assembly language programming, and understanding their differences and appropriate use cases is important for efficient and effective programming. 1. Indirect Addressing Mode:This is the mode of addressing where the instruction contains the address of the location where the target address is stored. So in this way, it is Indirectly storing the address of the target location in another memory location. So it is called Indirect Addressing mode....

Introduction: In computer organization, instruction formats refer to the way instructions are encoded and represented in machine language. There are several types of instruction formats, including zero, one, two, and three-address instructions. Here is a brief overview of each: Zero-address instructions: These instructions do not specify any operands or addresses. Instead, they operate on data stored in registers or memory locations implicitly defined by the instruction. For example, a zero-address instruction might simply add the contents of two registers together without specifying the register names. One-address instructions: These instructions specify one operand or address, which typically refers to a memory location or register. The instruction operates on the contents of that operand, and the result may be stored in the same or a different location. For example, a one-address instruction might load the contents of a memory location into a register. Two-address instructions: These instructions specify two operands or addresses, which may be memory locations or registers. The instruction operates on the contents of both operands, and the result may be stored in the same or a different location. For example, a two-address instruction might add the contents of two registers together and store the result in one of the registers. Three-address instructions: These instructions specify three operands or addresses, which may be memory locations or registers. The instruction ...