INSTRUCTION SETS

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INSTRUCTION SETS:

INSTRUCTION SETS A Presentation by- Ajay Mishael 12JJSB6111

WHAT IS INSTRUCTION SET?:

WHAT IS INSTRUCTION SET? Instruction Set is a part of the computer that pertains to programming, which is basically machine language. An instruction code is a group of bits that instruct the computer to perform a specific operation. There many parts in an instruction set like addressing modes, instructions native data types, registers, memory architecture, interrupt and exception handling etc. It is usually divided into two parts: Opcode and operand. The opcode is a group of bits that define operations and operand specifies the address of the operand and the address where the result has to be stored.

16 BIT INSTRUCTION SET FORMAT:

16 BIT INSTRUCTION SET FORMAT Sometimes the last bit is used for I. I determines whether the address provided is a direct address or an indirect address. If I= 0 then Direct address, If I=1 then Indirect address.

DIRECT AND INDIRECT ADDRESS:

DIRECT AND INDIRECT ADDRESS If the bits in the second part designate an address of a memory word in which the address of the operand is found, it is called Indirect address. If the second part of the instruction, specifies the address of an operand, It is said to have a Direct address.

TYPES OF INSTRUCTION FORMATS:

TYPES OF INSTRUCTION FORMATS In the instruction formats where the number of operand references may be fixed, descriptions of formats include zero address, one-address, three-address, and four-address. FOUR ADDRESS FORMAT: The instruction specifies the addresses of operands in memory, the address where result is stored and also the address where the next instruction is to be carried out is stored. Example: ADD P,Q,R,S

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THREE ADDRESS : The instruction specifies three addresses. In these fields, either a processor register or a memory operand can be specified. Example: ADD R1,R2,R3 It implies that R1=R2+R3 The general format is: opcode dest,src1,src2. TWO ADDRESS : They are most commonly used in commercial computers. Each address field can specify either a processor register or a memory word. Example : ADD,R1,R2 Implies that R1 = R1+R2 The general format is : opcode dest,src

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ONE ADDRESS: The availability of an accumulator register in a processor allows intermediate results to be kept in it and subsequently used without unnecessary storing and retrieving from memory. Then only one address is sufficient. All operations are done between the AC register and a memory operand. Example : ADD B Implies that AC = AC + B The general format is : opcode src

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ZERO ADDRESS : There are instructions where the location of operands is defined implicitly. The operands are stored in a stack. The name “ zero address “ is given to this type of computer because of the absence of an address field in the computational instructions. Example : PUSH A pushes A on top of the stack. POP Y deletes an elements from the top of stack.

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COMPUTER INSTRUCTIONS CATEGORIES Data Transfer Instruction: Instruction Name Mnemonics Load LD Store ST Move MOV Input IN Output OUT Push PUSH Name Mnemonics Increment INC Decrement DEC Add ADD Multiply MUL Divide DIV Add with carry ADDC Data Manipulation Instructions

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Name Mnemonics Branch BR Jump JMP Skip SKP Call CALL Return RET Test TST PROGRAM CONTROL INSTRUCTIONS

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Computers provide an extensive set of instructions to give the user the flexibility to carry out various computational tasks. The instruction set of different computers differ from each other mostly in the way the operands are determined from the address and mode fields. CONCLUSION

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