Architecture of 8086 microprocessor

8086 Microprocessor is an enhanced version of 8085 Microprocessor that was designed by Intel in 1976. It is a 16-bit Microprocessor having 20 address lines and 16 data lines that provides up to 1MB storage. In April 1978, intel introduced this microprocessor and it was officially released on June 8.

1. Architecture of 8086 microprocessor MICROPROCESSOR AND EMBEDDED SYSTEMS

2. Group Member: ANIRBAN SAHA ANIK ( 18-36207-1 ) BISHOWJIT DATTA ( 18-37372-1 ) JOYDEEP KARMOKER ( 16-33028-3 ) LUTFA NOOR LABONY ( 18-36187-1 )

3. Overview In April 1978, Intel introduced its first 16 bit microprocessor. Production started in May, eventually, the 8086 was officially released on June 8.

4. INTERNAL ARCHITECTURE 8086 has two blocks BIU and EU. BIU contains Instruction queue, Segment registers, Instruction pointer, Address adder, the Address Summing block (Σ) EU contains Control circuitry, Instruction decoder, ALU, Pointer and Index register, Flag register.

5. Bus Interface Unit (BIU) The bus control logic of the BIU generates all the bus control signals such as read and write signals for memory and I/O. This unit handles all transfer of data and addresses on the buses for the EU(execution unit).

6. Bus Interface Unit (BIU) Main Components are- Instruction Queue Segment Registers Instruction Pointer

7. Bus Interface Unit (BIU) The function of BIU is to : Fetch the instruction or data from memory. Generate physical address . Write the data to the memory and port . Supports pipelining in instruction queue .

8. Execution Unit (EU) Execution Unit also called a functional unit An execution unit is a part of the central processing unit (CPU) that performs the operations and calculations as instructed by the computer program

9. Execution Unit (EU) Main components are- Instruction Decoder Control System Arithmetic Logic Unit General Purpose Registers Flag Register Pointer & Index registers

10. Execution Unit (EU) The functions of execution unit are : To tell BIU where to fetch the instructions or data from. To decode the instructions. To execute the instructions.

11. Features of 8086 Microprocessor It was the first 16-bit microprocessor. This microprocessor had major improvement over the execution speed of 8085. It is available as 40-pin Dual-Inline-Package (DIP). It is available in three versions: 8086 (5 MHz) 8086-2 (8 MHz) 8086-1 (10 MHz) It consists of 29,000 transistors.

12. Features of 8086 Microprocessor 8086 is designed to operate in two modes, Minimum and Maximum. It can pre-fetches up to 6 instruction bytes from memory and queues them in order to speed up instruction execution. It requires +5V power supply. A 40 pin dual in line package. Address ranges from 00000H to FFFFFH

13. General Purpose Registers We have discussed general purpose registers as being discrete memory locations within the CPU used to hold temporary data and instructions. However there are also special purpose registers. A special purpose register is one that has a specific control or data handling task to carry out.

14. Type Of General Purpose Registers AX - the accumulator register Arithmetic, logic and data transfer Multiplication & Division Input & Output BX - the base address register BX register is an address register. It usually contain a data pointer used for based, based indexed

15. Type Of General Purpose Registers CX - the count register Iterative code segments using the LOOP instruction Repetitive operations on strings with the REP command DX - the data register Data register can be used as a port number in I/O operations. It is also used in multiplication and division.

16. Pointers and index registers The pointers contain within the particular segments. The pointers IP, BP, SP usually contain offsets within the code, data and stack segments respectively SI - Source index register DI - Destination index register BP – Base pointer SP - Stack pointer

17. Pointers and index registers Used to keep offset addresses. Used in various forms of memory addressing. In the case of SP and BP the default reference to form a physical address is the Stack Segment (SS-will be discussed under the BIU) The index registers (SI & DI) and the BX generally default to the Data segment register (DS).

18. Flag Register 8086 has a 16-bit flag register Contains 9 active flags There are two types of flags in 8086 Conditional flags – six flags, set or reset by EU on the basis of results of some arithmetic operations Control flags – three flags, used to control certain operations of the processor

19. Conditional Flags Control Flags Trap Flag (TP) Interrupt Flag (IF) Direction Flag (DF) Carry Flag (CF) Parity Flag (PF) Auxiliary Flag (AF) Sign Flag (SF) Overflow Flag (OF) Zero Flag (ZF)

20. Memory Segmentation 8086 has a 20-bit address bus So it can address a maximum of 1MB of memory. 8086 can work with only four 64KB segments at a time within this 1MB range. These four memory segments are called Code segment (CS) Stack segment (SS) Data segment (DS) Extra segment (ES)

21. Segment Code Segment That part of memory from where BIU is currently fetching instruction code bytes Stack Segment A section of memory set aside to store addresses and data while a subprogram executes Data & Extra Segments Used for storing data values to be used in the program

22. Instruction Pointer (IP) Register A 16-bit register Holds 16-bit offset, of the next instruction byte in the code segment . BIU uses IP and CS registers to generate the 20-bit address of the instruction to be fetched from memory . The CS register contains the segment number of the next instruction and IP contains the offset.

23. Applications of 8086 microprocessor Gaming devices. Mobile phones. Laptops and some electronic gadgets. Traffic Lights Controller. Washing Machines. Microwave ovens. Frequency counters and synthesizers. Digital Clocks.

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