8085 Microprocessor

INTRODUCTION

The most important technological invention of modern times is the “microprocessor”. A microprocessor is a multiple purpose programmable clock driven, register based electronic device that reads binary instructions from memory, accepts binary data as input and processing this data according to the instructions written in the memory. The microprocessor is capable of performing computing functions and making decisions to change the sequence of program execution. The microprocessor can be embedded in a larger system, and can function as the CPU of a computer called a microcomputer.

The Figure shows the basic block diagram of a microcomputer which processes binary data and traditionally represented by four blocks i.e. CPU, memory, input device and output device.

Here, input device is a device that transfers information from outside world to the computer for example: 

Key board, mouse, webcam, microphone, scanner, electronic white boards, etc. The output device transfers information from computer to the outside world like monitor, printers (all types), speakers, headphones, projector, plotter, Braille embosser, LCD projection panel, computer output microfilm (COM) etc. Memory is an electronic medium that stores binary information.
Central Processing Unit (CPU) is the heart of computer systems. The microprocessors in any microcomputer act as a CPU. The CPU can be made up with ALU + CU + Registers, where ALU is the group of circuits that perform arithmetic and logical operations. Control Unit (CU) is a group of circuits that provide timings and signals to all the operations in the computer and controls the data flow.
Microcontroller is a programmable device that includes microprocessor, memory and I/O signal lines on a single chip, fabricated using VLSI technology. Microcontrollers are also known as single chip microcomputers. They are mostly used to perform dedicated functions such as automatic control of equipment, machines and process in industries and consumer appliances.

HISTORY OF MICROPROCESSORS

A brief review of certain microprocessors were given in the Table. Intel introduced its first 4-bit PMOS microprocessor 4004 in the year 1971. It has 16 pins, 640-bytes of memory addressing capability and 10 address lines. After this enhanced version of 4004, a 4-bit, Intel 4040 was developed. In 1972, Intel introduced its first 8-bit processor Intel 8008, which also uses PMOS technology. The PMOS technology processors were slow and not compatible with TTL logic. These microprocessors could not survive as general purpose microprocessor due to design limitations. In 1974, Intel introduced its more powerful and faster 8 bit NMOS microprocessor Intel 8080. These processors were faster and compatible with TTL logic. Intel 8085 followed 8080 microprocessor. The main limitations of 8 bit microprocessors tempted the designers to go for more powerful processors in terms of advanced architecture, more processing capability, larger memory addressing capability and more powerful instruction set. The Intel 8086 was the result, launched in 1978 . The technology used was HMOS, high speed and high performance MOS technology.

Note: Most of the general purpose microprocessors used in the modern world computers are the family of 8086.