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| basic blocks of processor |
Processor
A
processor is the logic circuitry that responds to and processes the basic instructions
that drives a computer. The term processor has generally replaced the term
central processing unit (CPU). The
processor in a personal computer or embedded in small devices is often called a
microprocessor.
A central processing unit (CPU) is the electronic circuitry within a computer that
carries out the instructions of a computer program by
performing the basic arithmetic, logical, control and input/output (I/O)
operations specified by the instructions. The term has been used in the
computer industry at least since the early 1960s. Traditionally, the term CPU refers to
a processor, more specifically to its processing unit and control unit (CU),
distinguishing these core elements of a computer from external components such
as main memoryand I/O
circuitry. The block diagram of basic processor is as shown in the figure1.
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| basic processor |
Figure 1
Basic processor
Basic blocks of processor :
ALU
An arithmetic logic unit (ALU) is
a digital electronic circuit that
performs arithmetic and bitwise
logical operations on integer binary
numbers. This is in contrast to a floating-point unit(FPU), which operates
on floating point numbers. An ALU is a
fundamental building block of many types of computing circuits, including
the central processing unit (CPU) of
computers, FPUs, and graphics processing units (GPUs). A
single CPU, FPU or GPU may contain multiple ALUs.
The
inputs to an ALU are the data to be operated on, called operands, and a code indicating the
operation to be performed; the ALU's output is the result of the performed
operation. In many designs, the ALU also exchanges additional information with
a status register, which relates to the result of the
current or previous operations. The diagram of ALU is as shown in the
figure2.
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| alu |
Figure2 Arithmetic Logic Unit
Control
Unit
The control unit (CU)
is a component of a computer's central processing unit (CPU) that directs operation of the processor. It tells
the computer's memory, arithmetic/logic unit and input and output devices how to respond to a
program's instructions.
The Control
Unit (CU) is digital circuitry contained within the processor that coordinates
the sequence of data movements into, out of, and between a processor's many
sub-units. The result of these routed data movements through various digital
circuits (sub-units) within the processor produces the manipulated data
expected by a software instruction (loaded earlier, likely from memory). The
diagram of control unit is as show in the figure3.
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| control unit |
figure3 : control unit
Registers
A register is a quickly accessible location available to a
digital processor's central processing
unit (CPU).
Registers usually consist of a small amount of fast storage, although some registers have
specific hardware functions, and may be read-only or write-only. Registers are
typically addressed by mechanisms other than main memory, but may in some cases be memory mapped.
Almost
all computers, whether load-store
architecture or not, load data from a larger memory into registers
where it is used for arithmetic operations and is manipulated or tested by machine instructions. Manipulated data is then often
stored back to main memory, either by the same instruction or a subsequent one.
Modern processors use either static or dynamic RAM as main memory, with the
latter usually accessed via one or more cache levels. Processor registers are normally at the top of the memory hierarchy, and provide the fastest way to access data. The term
normally refers only to the group of registers that are directly encoded as
part of an instruction, as defined by the instruction set. The diagram of register unit is as shown in the figure4.
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| register unit |
Figure4. Register Unit
Program Counter
The Program Counter is a register which is also known as PC.
PC contains the memory address of the next instruction to be executed. In the
beginning PC contains the address of the memory location where the program
begins. Here, the program counter is a 32 bit register which needs a 32 bit
input and a clock. The output obtained is a 32 bit register. Instructions are usually fetched sequentially from memory,
but control transfer instructions
change the sequence by placing a new value in the PC. These include branches (sometimes called jumps), subroutine calls, and returns. A transfer that is conditional on the truth of some
assertion lets the computer follow a different sequence under different
conditions. The diagram of program counter is as shown in the figure5.
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| pc |
Figure5 Program Counter
Data Memory
The Data Memory Register is also known as Memory
Data Register. The Memory Data Register is the register of a computer's control unit that contains the data to
be stored in the computer storage (e.g. RAM), or the data after a fetch from the computer storage. It
acts like a buffer and holds anything that is copied from the memory ready for
the processor to use it.
The MDR is a two-way register. When data is fetched from
memory and placed into the MDR, it is written to go in one direction. When
there is a write instruction, the data to be written is placed into the MDR
from another CPU register, which then puts the data into memory.
The Data Memory Register is half of a minimal interface between a microprogram and computer storage, the other half is a memory address register .
The Memory Data Register
(MDR) contains the data value being fetched or stored. It is a common mistake
to say that the MDR should be W bits wide, where W is the cell size. However,
on most computers the cell size is only 8-bits, and most data values occupy
multiple cells. Thus, the size of the MDR is usually a multiple of 8 bits.
Typical values of MDR width are 32 and 64 bits, which would allow us to fetch,
in a single step, either an integer or a float value.
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