CH5 - Basic Computer Organization & Design BASIC...

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1 Basic Computer Organization & Design BASIC COMPUTER ORGANIZATION AND DESIGN • Instruction Codes • Computer Registers • Computer Instructions • Timing and Control • Instruction Cycle • Memory Reference Instructions • Input-Output and Interrupt • Complete Computer Description • Design of Basic Computer • Design of Accumulator Logic
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2 Basic Computer Organization & Design INSTRUCTION CODES Program: A set of instructions that specify the operations , operands , and the sequence by which processing has to occur Instruction Code: A group of bits that tells the computer to perform a specific operation Instruction codes Instruction Code Format: - Operation code: • A group of bits that define the operation (add, subtract, shift) • The operation (or macrooperation) specifies a set of microoperations - Operand (or address of operand) • Data stored in registers or in the memory, on which the operation is to be performed Opcode Operand (or Address)
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3 Basic Computer Organization & Design STORED PROGRAM ORGANIZATION Instruction codes Opcode Address Instruction Format Binary Operand Operands (data) Processor register (Accumulator or AC) Memory 4096 x 16 15 12 11 0 15 0 Instructions (program) 15 0 4 bits 12 bits 2 4 = 16 operations 2 12 = 4096 words
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4 Basic Computer Organization & Design ADDRESSING MODES Instruction codes Opcode Operand (or Address) Instruction Format Direct Address Mode Second part of instruction specifies the address of an operand Indirect Address Mode Second part of instruction specifies an address of a memory word in which the address of the operand is found Immediate Mode Second part of instruction specifies an operand
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5 Basic Computer Organization & Design INDIRECT ADDRESS Effective Address(EFA, EA) The address of the operand in a computation-type instruction, or the target address in a branch-type instruction Instruction codes 0 ADD 457 22 Operand 457 + AC Direct Address 1 ADD 300 35 1350 300 Operand 1350 + Indirect address Effective Address Opcode Address Instruction Format 15 14 12 0 I 11 I = 0 Direct address I = 1 Indirect address
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6 Basic Computer Organization & Design COMPUTER REGISTERS Registers Registers in the Basic Computer (BC) 11 0 PC 15 0 IR 15 0 TR 7 0 OUTR 15 0 DR 15 0 AC 0 AR INPR 0 7 Memory 4096 x 16 List of BC Registers Symbol # of bits Name Function DR 16 Data Register Holds memory operand AR 12 Address Register Holds address for memory AC 16 Accumulator Processor register IR 16 Instruction Register Holds instruction code PC 12 Program Counter Holds address of instruction TR 16 Temporary Register Holds temporary data INPR 8 Input Register Holds input character OUTR 8 Output Register Holds output character
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7 Basic Computer Organization & Design COMMON BUS SYSTEM Registers S2 S1 S0 Bus Memory unit 4096 x 16 LD INR CLR Address Read Write AR LD INR CLR PC LD INR CLR DR LD INR CLR AC Adder and logic E INPR IR LD LD INR CLR TR OUTR LD Clock 16-bit common bus 7 1 2 3 4 5 6 S2 S1 S0 selected register 0 0 0 none 0 0 1 AR 0 1 0 PC 0 1 1 DR 1 0 0 AC 1 0 1 IR 1 1 0 TR 1 1 1 Memory Bus Selection AC extended bit flip-flop for carry-out and circulation
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CH5 - Basic Computer Organization & Design BASIC...

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