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' you can do the second part in c Background Basic Computer Model - Von Neumann Model Von Neumann computer systems contain three main
you can do the second part in c Background Basic Computer Model Von Neumann Model Von
Neumann computer systems contain three main building blocks: the central processing unit CPU
memory, and inputoutput devices IO These three components are connected together using the
system bus. The most prominent items within the CPU are the registers: they can be manipulated directly
by a computer program, See figure one: Function of the Von Neumann Component: Memory: Storage of
information dataprogram Processing Unit: ComputationProcessing of Information Input: Means of
getting information into the computer. eg keyboard, mouse Output: Means of getting information out
of the computer. eg printer, monitor Control Unit: Makes sure that all the other parts perform their tasks
correctly and at the correct time. General Registers: The number of registers in a processor unit may vary
from one processor to another. Below are the general registers used by most processor: One of the CPU
registers is called as an accumulator or A register. It is the main operand register of the ALU. it is used
to store the result generated by ALU. The data register MDR acts as a buffer between the CPU and main
memory. It is used as an input operand register with the accumulator. The instruction register IR holds
the opcode of the current instruction. The address register MAR holds the address of the memory in
which the operand resides. The program counter holds the address of the next instruction to be
fetched for execution. Additional addressable registers can be provided for storing operands and
address. This can be viewed as replacing the single accumulator by a set of registers. If the registers are
used for many purpose, the resulting computer is said to have general register organization. In the case
of processor registers, a registers is selected by the multiplexers that form the buses. Communication
Between Memory processing Unit Communication between memory and processing unit consists of two
registers: Memory Address Register MAR Memory Data Register MDR To read, The address of the
location is put in MAR. The memory is enabled for a read. The value is put in MDR by the memory. To
write, The address of the location is put in MAR. The data is put in MDR The Write Enable signal is
asserted. The value in MDR is written to the location specified. Generic CPU Instruction Cvcle The generic
instruction cycle for an unspecified CPU consists of the following stages: Fetch instruction: Read
instruction code from address in PC and place in IR IRlarrMemory Decode instruction: Hardware
determines what the opcodefunction is and determines which registers or memory addresses contain
the operands. Fetch operands from memory if necessary: If any operands are memory addresses, initiate
memory read cycles to read them into CPU registers. If an operand is in memory, not a register, then the
memory address of the operand is known as the effective address, or EA for short. The fetching of an
operand can therefore be denoted as Register larr Memory EA On today's computers, CPUs are much
faster than memory, so operand fetching usually takes multiple CPU clock cycles to complete. Execute:
Perform the function of the instruction. If arithmetic or logic instruction, utilize the ALU circuits to carry
out the operation on data in registers. This is the only stage of the instruction cycle that is useful from the
perspective of the end user. Everything else is overhead required to make the execute stage happen.
One of the major goals of CPU design is to eliminate overhead, and spend a higher percentage of the
time in the execute stage. Details on how this is achieved is a topic for a hardware focused course in
computer architecture. Store result in memory if necessary: If destination is a memory address, initiate a
memory write cycle to transfer the result from the CPU to memory. Depending on the situation, the CPU
may or may not have to wait until this Below is an example of a full instruction cycle which uses memory
addresses for all three operands. mull product Fetch the instruction code from MemoryPC Decode
the instruction. This reveals that it's a multiply instruction, and that the operands are memory locations
and product. Fetch and from memory. Multiply and storing the result in a CPU register. Save
the result from the CPU to memory location product. Addressing Modes The term addressing modes
refers to the way in which the operand of an instruction is specified. Information contained in the
instruction code is the value of the operand or the address of the resultoperand Following are the main
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