SIMPLE LOGIC OF MICROPROCESSOR

A microprocessor performs a collection of machine instructions that the processor what to say. Based on the instructions, a microprocessor does three basic things:

* Using the ALU (Arithmetic / Logic Unit), a microprocessor can perform mathematical operations like addition, subtraction, multiplication and division. Modern microprocessors contain complete floating point processors that can perform extremely sophisticated operations on large floating point numbers.
* A microprocessor can move data from one memory location to another.
* A microprocessor can make decisions and jump to a new set of instructions based on those decisions.

It can be very sophisticated things that a microprocessor does, but those are its three basic activities. The following diagram shows an extremely simple microprocessor that can do three things:
This is about as simple as a microprocessor gets. This microprocessor has:

* An address bus (which can be 8, 16 or 32 bits wide) that sends an address in memory
* A data bus (which can be 8, 16 or 32 bits wide) that the data in memory can send or receive data from memory
* A RD (read) and WR (write) line to memory, whether he wants to establish whether the recipient site to get say
* A clock line that lets a clock pulse sequence the processor
* A reset line that the program.

HOW A MICROPROCESSOR WORKS

The microprocessor is the heart of a normal computer, whether it is a desktop machine, a server or a laptop. The microprocessor you are using may be a Pentium, a K6, a PowerPC, a Sparc or any of the many different brands and types of microprocessors, but they all do roughly the same in the same way.

A microprocessor - also known as a CPU or central processing unit - is a complete calculation engine that is manufactured on a single chip. The first microprocessor was the Intel 4004, introduced in 1971. The 4004 was not very powerful - all it could do was add and subtract, and it could only do that 4 bits at a time. But it was amazing that everything on one chip. Prior to 4004, engineers built computers either from collections of chips or from discrete components (transistors one at a time). The 4004 powered one of the first portable electronic calculators.

INTELS 8 BIT PROCESSORS

8008:-

• Introduced April 1, 1972
• Clock rate 200 kHz (8008–1: 800 kHz)
• 0.05 MIPS
• Bus Width 8 bits (multiplexed address/data due to limited pins)
• Enhancement loadPMOS logic
• Number of Transistors 3,500 at 10 µm
• Addressable memory 16 KB
• Typical in early 8 bit microcomputers, dumb terminals, general calculators, bottling machines
• Developed in tandem with 4004.

8080:-

• Introduced April 1, 1974
• Clock rate 2 MHz
• 0.64 MIPS
• Bus Width 8 bits data, 16 bits address
• Enhancement load NMOS logic
• Number of Transistors 6,000
• Assembly language downwards compatible with 8008.
• Addressable memory 64 KB
• Up to 10X the performance of the 8008.

8085:-

• Introduced March 1976
• Clock rate 2 MHz^]
• 0.37 MIPS
• Bus Width 8 bits data, 16 bits address
• Depletion loadNMOS logic.
• Number of Transistors 6,500 at 3um