instruction set


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Complete instruction set (format) : 

Complete instruction set (format) By Hiren Sardhara

Slide 2: 

Introduction An instruction is normally made up of a combination of an operation code and some way of specifying an operand, most commonly by its location and address in memory though non memory reference instruction can exists.

Objectives of instruction : 

Objectives of instruction Understand the factors involved in instruction set architecture design. Gain familiarity with memory addressing modes. Understand the concepts of instruction-level pipelining and its affect upon execution performance.

Types of computer instructions : 

Types of computer instructions Four address instruction Three address instruction Two address instruction One address instruction Zero address instruction

Four address instruction:- : 

Four address instruction:- The instruction specifies the address of operands in memory, the address where results is stored and also the address where the next instruction to be carried out is stored Example:-ADD P,Q,R,S P and Q address of two operands R is address of memory where result is stored S is location of next instruction to be executed.

Three address instruction:- : 

Three address instruction:- The instruction specifies three address. In these fields, either a processor register or a memory operand can be specified. Example:- ADD R1,R2,R3 implies R1R2+R3 The general format is dest [src1] op [src2]

Two address instruction:- : 

Two address instruction:- They are most commonly used in commercial computers. The first operand listed in the instruction is assumed to be both a source and destination where the result of the operation is stored. Example:- ADD R1,R2 implies R1R1+R2

One address instruction:- : 

One address instruction:- The operations which are done between the AC register and a memory operand. For these kind of operations the one address instruction is used. By default , the accumulator will be used for all data manipulation Example:- ADD B implies AC[AC]+[B]

Zero address instruction:- : 

Zero address instruction:- There are instruction where the location of operands is denied implicitly. The operands are stored in a stack. Stack is a sequence of memory locations where data can be inserted and deleted from only one end called top of the stack. Stack is in generally last-in-first-out format. Example:- PUSH A pushes A onto the top of the stack.

Addressing : 

Addressing Addressing modes specify where an operand is located. They can specify a constant, a register, or a memory location. The actual location of an operand is its effective address. Certain addressing modes allow us to determine the address of an operand dynamically.

Slide 11: 

Addressing Immediate addressing is where the data is part of the instruction. Direct addressing is where the address of the data is given in the instruction. Register addressing is where the data is located in a register. Indirect addressing gives the address of the address of the data in the instruction. Register indirect addressing uses a register to store the address of the address of the data.

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