Information Representation: Machine InstructionsReview: Computer OrganizationRegisters – Program CounterRegisters – Memory Address RegisterRegisters – Instruction RegisterIR StructureRegisters – Memory Buffer RegisterRegisters - AccumulatorArithmetic Logic UnitMemoryFetch/Execute CycleFetch cycleExecute CycleTypes of OpcodesLOAD ACC, memoryADD ACC, memoryxComputer AppletxComputer InstructionsSample OpcodesSemantic GapReal-life Example: Pentium 4.Pentium 4 ADDPentium 4 Add (cont)AcknowledgementsDale RobertsDepartment of Computer and Information Science,School of Science, IUPUICSCI 230Dale Roberts, LecturerDale Roberts, [email protected]@cs.iupui.eduInformation Representation: Machine InstructionsDale RobertsReview: Computer OrganizationReview: Computer OrganizationA Typical Von-Neumann ArchitectureA Typical Von-Neumann ArchitectureExample:Example:InputInput unit unitOutputOutput unit unit MemoryMemory unit unit Arithmetic and logicArithmetic and logic unit (ALU) unit (ALU) Central processingCentral processing unit (CPU) unit (CPU) Secondary storageSecondary storage unit unit Control Circuit(ex: PC: Program Counter)ALUMemory I/OCPUDale RobertsRegisters – Program CounterRegisters – Program CounterProgram Counter (PC)Program Counter (PC)Contains the memory address of Contains the memory address of the next instruction to be the next instruction to be executed. The contents of the executed. The contents of the program counter are copied to program counter are copied to the the memory address registermemory address register before an instruction is before an instruction is fetched from memory. At the fetched from memory. At the completion of the fetched completion of the fetched instruction, the instruction, the control unitcontrol unit updates the program counter updates the program counter to point to the next instruction to point to the next instruction which is to be fetched.which is to be fetched.Dale RobertsRegisters – Memory Address RegisterRegisters – Memory Address RegisterMemory Address Register Memory Address Register (MAR)(MAR)A register located on the A register located on the central processing unitcentral processing unit which is in turn which is in turn connected to the address connected to the address lines of the system. This lines of the system. This register specifies the register specifies the address in memory where address in memory where information can be found information can be found and can be also used to and can be also used to point to a memory point to a memory location where location where information is to be information is to be stored.stored.Dale RobertsRegisters – Instruction RegisterRegisters – Instruction RegisterInstruction Register (IR)Instruction Register (IR)A register located on the A register located on the central processing unitcentral processing unit which holds the contents which holds the contents of the last instruction of the last instruction fetched. This instruction fetched. This instruction is now ready to be is now ready to be executed and is accessed executed and is accessed by the by the control unitcontrol unit..Dale RobertsIR StructureIR StructureThe Instruction Register typically has a The Instruction Register typically has a structure that includes operation code and an structure that includes operation code and an optional operand.optional operand.Everyone calles the operation code an Everyone calles the operation code an “Opcode”“Opcode”It is up to the manufacturer to determine how It is up to the manufacturer to determine how many bits comprise an instruction, and which many bits comprise an instruction, and which bits store the opcode and operand.bits store the opcode and operand.Dale RobertsRegisters – Memory Buffer RegisterRegisters – Memory Buffer RegisterMemory Buffer Register (MBR)Memory Buffer Register (MBR)A register located on the A register located on the central processing unitcentral processing unit which which is in turn connected to the data is in turn connected to the data lines of the system. The main lines of the system. The main purpose of this register is to purpose of this register is to act as an interface between the act as an interface between the central processing unitcentral processing unit and and memory. When the appropriate memory. When the appropriate signal is received by the signal is received by the control unitcontrol unit, the memory , the memory location stored in the memory location stored in the memory address register is used to address register is used to copy data from or to the copy data from or to the memory buffer register.memory buffer register.Dale RobertsRegisters - AccumulatorRegisters - AccumulatorAccumulator (ACC)Accumulator (ACC)A register located on the central processing unit. A register located on the central processing unit. The contents can be used by the arithmetic-The contents can be used by the arithmetic-logic unit for arithmetic and logic operations, logic unit for arithmetic and logic operations, and by the memory buffer register. Usually, all and by the memory buffer register. Usually, all results generated by the arithmetic-logic unit results generated by the arithmetic-logic unit end up in the accumulator.end up in the accumulator.Dale RobertsArithmetic Logic UnitArithmetic Logic UnitArithmetic-Logic Unit (ALU)Arithmetic-Logic Unit (ALU)Performs arithmetic operations such as addition Performs arithmetic operations such as addition and subtraction as well as logical operations and subtraction as well as logical operations such as AND, OR and NOT. Most operations such as AND, OR and NOT. Most operations require two operands. One of these operands require two operands. One of these operands usually comes from memory via the usually comes from memory via the memory buffer registermemory buffer register, while the other is the , while the other is the previously loaded value stored in the previously loaded value stored in the accumulatoraccumulator. The results of an arithmetic-logic . The results of an arithmetic-logic unit operation is usually transfered to the unit operation is usually transfered to the accumulatoraccumulator..Dale RobertsMemoryMemoryMemory is made up of a series of zero's (0) and Memory is made up of a series of zero's (0) and one's (1) called bits or binary. These individual one's (1) called bits or binary. These individual bits are grouped together in lots of