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# Instruction code

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### Instruction code

1. 1. Instruction Codes Type of Instruction Codes Overview Unit 3 - Instruction Codes Abhineet Anand Computer Science and Engg. Department University of Petroleum and Energy Studies, Dehradun November 26, 2012 Abhineet Anand Unit 3 - Instruction Codes
2. 2. Instruction Codes Type of Instruction Codes Overview Introduction Operation Code Operands Instruction Codes A Computer instruction is binary code that speciﬁes a sequence of micro operation for the Computer. The Computer reads each instruction from memory and places it in a control register. The control then interprets the binary code of the instruction and proceeds to execute it by issuing a sequence of micro operations. Abhineet Anand Unit 3 - Instruction Codes
3. 3. Instruction Codes Type of Instruction Codes Overview Introduction Operation Code Operands Instruction Codes An instruction code is a group of bits that instruct the computer to perform a speciﬁc task. It is usually divided into parts, each having its own particular interpretation. They are: Operation Code, and Operands. The most basic part of an instruction code is its operation part. Abhineet Anand Unit 3 - Instruction Codes
4. 4. Instruction Codes Type of Instruction Codes Overview Introduction Operation Code Operands Operation Code The Operation Code (OpCode) of an instruction is a group of bits that deﬁne each operation such add, subtract, multiply, shift, and complement. It must consist of at least n bits for a given 2n distinct operations. Suppose we are having 64 (26 ) operation then the length of OpCode will be 6. The control unit decode the OpCode and do the required operation. Abhineet Anand Unit 3 - Instruction Codes
5. 5. Instruction Codes Type of Instruction Codes Overview Introduction Operation Code Operands Operands The Operation must be performed on some data stored in processor register or in memory. Every Computer has its own particular instruction code format. The Simplest way to organize a computer is to have an instruction code format with two parts. The ﬁrst part speciﬁes the operation to be performed and the second speciﬁes an address. Abhineet Anand Unit 3 - Instruction Codes
6. 6. Instruction Codes Type of Instruction Codes Overview Type of Instruction Codes Memory - Reference Instruction Register - Reference Instruction Input - Output Instruction Instruction Codes The Basic Computer has three instruction code formats. The OpCode part of the instruction contains three bits and the meaning of the remaining 13 bits depends on the operation code encountered. The three instruction code formats are: Memory - Reference Instruction Register - reference Instruction Input - Output Operation Abhineet Anand Unit 3 - Instruction Codes
7. 7. Instruction Codes Type of Instruction Codes Overview Type of Instruction Codes Memory - Reference Instruction Register - Reference Instruction Input - Output Instruction Memory - Reference Instruction A Memory-Reference instruction uses 12 bits to specify an address and one bit to specify the addressing mode I. I is equal to 0 for direct address and to 1 for indirect address. Abhineet Anand Unit 3 - Instruction Codes
8. 8. Instruction Codes Type of Instruction Codes Overview Type of Instruction Codes Memory - Reference Instruction Register - Reference Instruction Input - Output Instruction Register - Reference Instruction The Register - Reference instruction are recognized by the operation code 111 with 0 in the leftmost bit (bit 15) of the instruction. It speciﬁes an operation on or a test of the AC register. An operand from memory is not needed, so the other 12 bits are used to specify the operation or test to be executed. Abhineet Anand Unit 3 - Instruction Codes
9. 9. Instruction Codes Type of Instruction Codes Overview Type of Instruction Codes Memory - Reference Instruction Register - Reference Instruction Input - Output Instruction Input - Output Instruction An Input- Output Instruction does not need a reference to memory and recognized by the operation code 111 with a 1 in the left most bit of the instruction. The remaining 12 bits are used to specify the type of input-output operation or test performed. Abhineet Anand Unit 3 - Instruction Codes
10. 10. Instruction Codes Type of Instruction Codes Overview How to know type of instruction. Table of Instruction. OverView The type of instruction is recognized from four bits in position 12 through 15 of the instruction. If the three opcode in position 12 to 14 are not equal to 111, the instruction is a memory-reference type. If these bit position is equal to 111 and 15th position is 0, the instruction is a register-reference type otherwise it is Input- output type. Abhineet Anand Unit 3 - Instruction Codes
11. 11. Instruction Codes Type of Instruction Codes Overview How to know type of instruction. Table of Instruction. Becuase of three bits use in the operation code, its seems that the computer is restricted to a maximum of eight distinct operations. However, by using other 12 bits, the total number of instruction can exceed eight. In fact, the total number of instruction chosen for the basic computer is equal to 25. Abhineet Anand Unit 3 - Instruction Codes
12. 12. Instruction Codes Type of Instruction Codes Overview How to know type of instruction. Table of Instruction. Table of Instruction. The symbol designation is a three-letter word and represents an abbreviation intended for programmers and users. Memory Reference Instructions Abhineet Anand Unit 3 - Instruction Codes
13. 13. Instruction Codes Type of Instruction Codes Overview How to know type of instruction. Table of Instruction. Table of Instruction Register Reference Instructions Abhineet Anand Unit 3 - Instruction Codes
14. 14. Instruction Codes Type of Instruction Codes Overview How to know type of instruction. Table of Instruction. THANK YOU Abhineet Anand Unit 3 - Instruction Codes