instruction codes
- 1. S.AZHAGARAMMAL M.SC (INFO TECH) NADAR SARASWATHI COLLEGE OF ARTS AND SCIENCE THENI. INSTRUCTION CODES:
- 2. INSTRUCTION CODES: It is usually divided into parts, each having its own particular interpretation. Computer instruction are the basic components of a machine language program. They are also known as macro operations.
- 3. Each instruction initates a sequence of micro operation that often operands from register or memory, possibly perfrom arithmetic. Logic or shift operation and store results in register or memory. Instruction are encoded as binary instruction codes.
- 4. Each instruction code contains of a operation code or people which designates the overall purpose of instruction. (e.g) add, substract, move , input, etc)
- 5. In addition to the opcode many instruction also contains are more operands which indicate where in register of memory the data. (e.g) add instruction requires two operands 15 12 11 0 Opcode address
- 6. OPERATION CODE: The operation code of an instruction is a group of bits that define such operation as, add subtract, multiples. Shift and complement. The number of operation available in the operation code of an instruction depends on the number of operation available in the computer.
- 7. The total number of operation available in the computer of at least n bits for a given 2n (orless) distinct operation. As an illustration consider a computer with 64 distinct operation one of them being an ADD operation. For this reason an operation code is sometimes called a micro operation because it specifies a set of micro operations.
- 8. Operations are most often encode as unsigned binary numbers in order to minimize the number of bits used to store them. (ex) 4-bit opcode encoded as a binary number up to 16 different operations.
- 9. The register and then generating the control signals necessary to drive all other hardware in the CPU to perform the sequence of micro operations that comprise the instruction. Memory words can be specified in instruction codes by their address. Processor register can be specified by assiging to the instruction another code of k bits that specifies one of 2k registers.
- 11. ADDRESS BUS Address bus Data bus Mahine instructions ------------------------ External memory(RAM)
- 12. STORED PROGRAM ORGANIZATION: In the won newmann architecture, machine instructions and data are stored in the same RAM during program execution. The first part specifies the operations to as performed and the second specifies an address.
- 13. If we store each instruction code in one 16 bits memory would we have available 4bits for the operation code to specify are all of 16 possible operation and 12bits to specify the address of an operands. The control ready a 16-bits instruction from the program portion of memory. It uses the 12-bits address part of the program portion of memory.
- 14. STORED PROGRAM ORGANIZATION: 15 12 11 0 Opcode address Binary operand Instruction (program) Operands (data) Process register (accumlator of AC)
- 15. ACCUMLATOR (AC) Computers that have a single processor resgister usually assign to it name accmulator and label it ac. The operation is performed with be memory operand and the content of ac. Operations such as ac and increment ac operate stored in the ac register.
- 16. INDIRECT ADDRESS: Immediate instruction When the second part of an instruction code specifies an operand the instruction is said to have an immediate operand. When the second part specifies the address of an operand the instruction is said to have direct addresss.
- 17. This a third is in on contrast to a third possinility caused an address. The mode bit is o for a direct address and 1 for indirect address. A direct address instruction it is places in address 22 in memory.
- 18. EFFECTIVE ADDRESS: The i bit is o so the instruction recongnized a direct address instruction. We define the effective address to be the address of the operand in a computation-type instruction or the target address in the branch type instruction. Thus the effective address in the computer instruction.
- 19. memory 15 14 10 1 (a) instruction format (b)direct address 1 opcode Address ADD 457 + Ac
- 20. memory 35 300 (c) Indirect address 1350 1 ADD 300 1350 operand
- 21. The pointer could placed in a processor register of memory as done in commercial computers.
- 22. THANK YOU