8086 Architecture - Electrical Engineering (EE) PDF Download

Introduction to 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.
• The processor (CPU, for Central Processing Unit) is the computer's brain. It allows the processing of numeric data, meaning information entered in binary form, and the execution of instructions stored in memory.

➢ Microcontrollers Vs Microprocessors 

• A microprocessor requires an external memory for program/data storage. Instruction execution requires movement of data from the external memory to the microprocessor or vice versa. Usually, microprocessors have good computing power and they have higher clock speed to facilitate faster computation.
• A microcontroller has required on-chip memory with associated peripherals. A microcontroller can be thought of a microprocessor with inbuilt peripherals.
• A microcontroller does not require much additional interfacing ICs for operation and it functions as a stand alone system. The operation of a microcontroller is multipurpose, just like a Swiss knife.
• Microcontrollers are also called embedded controllers. A microcontroller clock speed is limited only to a few tens of MHz. Microcontrollers are numerous and many of them are application-specific.

➢ Evolution of Microprocessor

• A microprocessor is used as the CPU in a microcomputer. There are now many different microprocessors available.
  (i) Microprocessor is a program-controlled device, which fetches the instructions from memory, decodes and executes the instructions. Most Micro Processor are single-chip devices.
  (ii) Microprocessor is a backbone of the computer system. which is called CPU.
  (iii) Microprocessor speed depends on the processing speed depends on DATA BUS WIDTH.
  (iv) A common way of categorizing microprocessors is by the no. of bits that their ALU can Work with at a time.
  (v)The address bus is unidirectional because the address information is always given by the Micro Processor to address a memory location of an input/output devices.

The data bus is Bi-directional because the same bus is used for the transfer of data between Micro Processor and memory or input/output devices in both the direction.

• It has limitations on the size of data. Most Microprocessor does not support floating-point operations.
• Microprocessor contains ROM chip because it contain instructions to execute data.
• What is the primary & secondary storage device? - In primary storage device the
• Storage capacity is limited. It has a volatile memory. In secondary storage device, the storage capacity is larger. It is a nonvolatile memory.

➢ Types of Storage Devices

• Primary Devices: RAM (Read / Write memory, High Speed, Volatile Memory) / ROM (Read-only memory, Low Speed, Non-Volatile Memory).
• Secondary Devices: Floppy disc / Hard disk.

➢ Compiler

• Compiler is used to translate the high-level language program into machine code at a time. It doesn’t require special instruction to store in memory; it stores automatically. The Execution time is less compared to Interpreter.

Types of Microprocessor

1. 4-Bit Microprocessor

• The first microprocessor (Intel 4004) was invented in 1971. It was a 4-bit calculation device with a speed of 108 kHz. Since then, microprocessor power has grown exponentially. 
• So what exactly are these little pieces of silicone that run our computers(" Common Operating Machine Particularly Used For Trade Education And Research ")
• It has 3200 PMOS transistors.
• It is a 4-bit device used in calculator.

2. 8-Bit Microprocessor

• In 1972, Intel came out with the 8008 which is 8-bit.
• In 1974, Intel announced the 8080 followed by 8085 is a 8-bit processor Because 8085 processor has 8 bit ALU (Arithmetic Logic Review). Similarly, 8086 processor has 16 bit ALU. This had a larger instruction set then 8080. used NMOS transistors, so it operated much faster than the 8008.
• The 8080 is referred to as a “Second-generation Microprocessor.”

➢ Limitations of 8 Bit Microprocessor

• Low speed of execution.
• Low memory addressing capability.
• Limited number of general-purpose registers.
• Less power full instruction set.

➢ Examples for 4/ 8 / 16 / 32 Bit Microprocessors

• 4-Bit processor – 4004/4040
• 8-bit Processor - 8085 / Z80 / 6800
• 16-bit Processor - 8086 / 68000 / Z8000
• 32-bit Processor - 80386 / 80486

➢ What are 1st / 2nd / 3rd / 4th Generation Processor?

• The processor made of PMOS technology is called 1^st generation processor, and it is made up of 4 bits.
• The processor made of NMOS technology is called 2^nd generation processor, and it is made up of 8 bits.
• The processor made of CMOS technology is called 3^rd generation processor, and it is made up of 16 bits.
• The processor made of HCMOS  technology is called 4t^h generation processor, and it is made up of 32 bits (HCMOS: High-density n-type Complementary Metal Oxide Silicon field-effect transistor).

Block Diagram of Microprocessor

(i) The Central Processing Unit (CPU)

• This device coordinates all operations of a microcomputer. It fetches programs stored in ROM‟s or RAMs and executes the instructions depending on a specific Instructions set, which is characteristic of each type of CPU, and which is recognized by the CPU.

(ii) The Random Access Memory (RAM): Temporary or Trail Programs are Written.

• Besides the ROM area, every computer has some memory space for temporary storage of data as well as for programs under development. These memory devices are RAMs or Read-write memory. 
• The contents of it are not permanent and are altered when power is turned off. So the RAM memory is considered to be a volatile memory.

(iii) The Read-Only Memory (ROM): Permanent Programs are Stored.

• The permanent memory device/area is called ROM because whatever be the memory contents of ROMs, they cannot be overwritten with some other information.
• For a blank ROM, the manufacturer supplies the device without any inf. In it, information can be entered electrically into the memory space. This is called burning a ROM or PROM.

(iv) Data Lines/Data Bus

• The number of data lines, like add. Lines vary with the specific CPU. The set of data lines is a database like the address bus, unlike add. 
• Bus, the data bus is bidirectional because while the information on the address Bus always flows out of the CPU; the data can flow both out of the CPU as well as into the CPU.

(v) Control Lines/ Control Bus

• The no. of control lines also depends on the specific CPU one is using.
  Example: Read; Write lines are examples of control lines

(vi) Clock

• The clock is a symmetrical square wave signal that drives the CPU

(vii) Instructions

• An instruction is an elementary operation that the processor can accomplish. Instructions are stored in the main memory, waiting to be processed by the processor. 
• An instruction has two fields:
  (i) Operation code, which represents the action that the processor must execute.
  (ii) Operand code, which defines the parameters of the action. The operand code depends on the operation. It can be data or a memory address.