The buses of microprocessor.

A bus is a collection of wires used to transmit signals in parallel. According to the purpose, the buses of a microcomputer can be divided into three types: address bus, data bus, and control bus.

1. Address Bus

The unidirectional address bus transmits the address signals emitted from CPU to memory and I/O port.
The address bus consists of 16, 20, 24 or 32 parallel signal lines.On these lines the CPU sends out the address of the memory location that is to be written to or read from. The no of memory location that the CPU can address is determined by the number of address lines. If the CPU has N address lines, then it can directly address 2N memory locations i.e. CPU with 16 address lines can address 216 or 65536 memory locations.

2. Data Bus

The signal on the bidirectional data bus is the data either from CPU to memory and I/O or from memory and I/O to CPU.The data bus consists of 8, 16 or 32 parallel signal lines. The data bus lines are bi-directional. This means that the CPU can read data in from memory or it can send data out to memory

3. Control Bus

The control bus is used to transmit the control signals such as read, write, and interrupt control signal. The control bus consists of 4 to 10 parallel signal lines.The CPU sends out signals on the control bus to enable the output of addressed memory devices or port devices.Typical control bus signals are Memory Read, Memory Write, I/O Read and I/O Write. 

Harvard architecture

 

Harvard Architecture based computer consist of separate memory spaces for the programs (or instruction) and data.

· Each memory space has its own address and data bus. Thus both instruction and data can fetch from memory concurrently.

· It provides significant processing speed improvement.

· There are two data and two address buses for the program and data memory spaces respectively.

· The program memory data bus and data memory data are multiplexed to form single data bus.

· Similarly, program memory Address and data memory address are multiplexed to form single address bus.

· Hence there are two blocks of RAM chips; one for program memory and another for data memory space.

· Data memory address unit generates data memory address. The data memory address bus carries the memory address of data where as program memory address bus carries the memory address of the instruction.

· Central arithmetic logic unit consists of the ALU, multiplier, Accumulator, etc.

· The program counter is used for next instruction to be fetched.

· Control unit control the sequence of operations to be executed.

· The data and control bus are bidirectional where as address bus is unidirectional.

Von-neuman architecture

A Von Neumann-based computer is a computer that:

· Uses a single processor.

· Uses one memory for both instructions and data. A von Neumann computer cannot distinguish between data and instructions in a memory location! It ‘knows’ only because of the location of a particular bit pattern in RAM.

· Executes programs by doing one instruction after the next in a serial manner using a fetch-decode-execute cycle.

1) The ALU, or Arithmetic Logic Unit
A Von Neumann CPU has an ALU. This is the part of the CPU that performs arithmetic and logic operations on data and acts as the revolving for the CPU, letting data enter and leave the CPU. We also know that CPUs have a ‘word size’. This is the number of bits that can be added, for example, in one go. The bigger a CPU’s word size, the more bits it can work on in one clock cycle and the more work you can get done.

2) The Control Unit
A Von Neumann CPU has a control unit. The control unit is in charge of ‘fetching’ each instruction that needs to be executed in a program by issuing control signals to the hardware. It then decodes the instruction and finally issues more control signals to the hardware to actually execute it.

3) Registers
A Von Neumann CPU has registers. These are very fast memory circuits. They hold information such as the address of the next instruction (Program Counter), the current instruction being executed (Current Instruction Register), the data being worked on and the results of arithmetic and logical operations (Accumulators), information about the last operation (Status Register) and whether an interrupt has happened (Interrupt Register). Registers are covered in a lot more detail later in this chapter.

4) The clock
Instructions are carried out to the beat of the clock! Some instructions take one beat and others more than one beat. Very roughly speaking, the faster the clock, the more clock beats you have per second so the more instructions per section you can do and the faster your computer will go.

5) Memory

• Memory, also called RAM (Random Access Memory),

– Consists of many memory cells (storage units) of a fixed size.
Each cell has an address associated with it: 0, 1, …

– All accesses to memory are to a specified address.
A cell is the minimum unit of access (fetch/store a complete cell).

– The time it takes to fetch/store a cell is the same for all cells.

• When the computer is running, both

– Program

– Data

are stored in the memory.

History of Microprocessor

4004:- The first commercially available Microprocessor was the Intel 4004 produced in 1971. It contained 2300 PMOS transistors.The 4004 was a 4 bit device intended to be used with some other devices in making a calculator.In 1972, Intel came out with the 8008, which was capable of working with 8 bit words.

8008 :- The 8008 however required 20 or more additional devices to form a functional CPU.

8080:- In 1974 Intel announced the 8080, which had a much larger instruction set than the 8008 and required only two additional devices to form a functional CPU.The 8080 used NMOS transistor, so it operated much faster than the 8008The 8080 is referred as a Second generation Microprocessor.It requires +5V,-5V and +12V supply.

8085:- In 1977, Intel Produced 8085, an upgrade of 8080 that required only a +5V supply.It was a 8 bit Microprocessor.

8088:- Intel Produced 8088, which was the first Microprocessor used in Personal computer by IBM. It has 16 bit registers and an 8 bit data bus and can address up to 1 million bytes of internal memory.

8086:- In 1978 Intel came out with the 8086 which is a full 16 bit Microprocessor.It has a 16 bit data bus and runs faster.It can address 220 or 1048576 memory locations.

80286:- Runs faster than the preceding processors, has additional capabilities and can address up to 16 million bytes.This processor can operate in real mode or in protected mode, which enables an operating system like windows to perform multitasking and to protect them from each other.

80386:-Has 32 bit registers and 32bit data bus.It can address up to 4 billion bytes of memory. The processor supports virtual mode, whereby it can swap portions of memory onto disk

80486:- Has 32 bit registers and 32 bit data bus.High speed cache memory connected to the processor bus enables the processor to store copies of the most recently used instructions and data.The processor can operate faster when using the cache directly without having to access the slower memory.

PENTIUM:-It has 32 bit registers, a 64 bit data bus and separate caches for data and for memory.The Pentium has a 5 Stage pipelined structure and the Pentium II has a 12 stage super pipelined structure.This feature enables them to run many operations in parallel.

Definition :- Mircoprocessor

 A microprocessor is an integrated circuit (IC) which incorporates core functions of a computer’s central processing unit (CPU). It is a programmable multipurpose silicon chip, clock driven, register based, accepts binary data as input and provides output after processing it as per the instructions stored in the memory. A processor is the brain of a computer which basically consists of Arithmetical and Logical Unit (ALU), Control Unit and Register Array. As the name indicates ALU performs all arithmetic and logical operations on the data received from input devices or memory. Register array consists of a series of registers like accumulator (A), B, C, D etc. which acts as temporary fast access memory locations for processing data. As the name indicates, control unit controls the flow of instructions and data throughout the system.