The 8086 microprocessor is a 16-bit processor designed by Intel in the late 1970s. It has a segmented memory architecture that supports a 16-bit ALU, registers, and memory addressing. Its architecture provides improvements over the 8085 including a 16-bit design, segmented memory addressing, and an instruction queue. The main components of the 8086 are the Bus Interface Unit (BIU) which contains the address adder, segment registers, and instruction queue, and the Execution Unit (EU) which contains registers, an ALU, and flag registers for status information.

1. ARCHITECTURE OF 8086MICROPROCESSOR
By
A.S.Krishna

2. What is a Microprocessor ?
A microprocessor incorporates the functions of a
computer's central processing unit (CPU) on a single
integrated circuit (IC), or at most a few integrated
circuits.
The microprocessor is a multipurpose, programmable
device that accepts digital data as input, processes it
according to instructions stored in its memory, and
provides results as output. It has internal memory.
Microprocessors operate on numbers and symbols
represented in the binary numeral system.

3. What is 8086 Microprocessor ?
The 8086 is also called iAPX 86. It is a 16-bit
microprocessor chip designed by Intel between early
1976 and mid-1978, when it was released.
It is notable as the processor used in the original IBM
PC.

4. Architecture of an 8086
Microprocessor
The architecture of 8086 provides a number of
improvements over 8085 architecture.
It supports a 16-bit ALU, a set of 16-bit registers
and provides segmented memory addressing
capability, a rich instruction set, powerful interrupt
structure, fetched instruction queue for overlapped
fetching and execution etc.,

6. Bus Interface Unit (BIU)
In the BIU we have some collection components. They
are:-
1. Address Adder.
2. Segment Registers and Program Counter.
3. Instruction Queue

7. 1. Address Adder
In the address adder the adder adds
the addresses and transfer them to the
memory though the internal data bus
path.

9. 2. Segment Registers and
Program Counter
Segment Registers
Code segment
Data segment
Stack segment
Extra segment
Segment Registers
CS
DS
SS
ES
Program Counter
IP
Program Counter
Instruction Pointer

11. 3. Instruction Queue
Instruction Queue
6
5
4
3
2
1
This a Queue which can
store the given instructions
one-by-one.

13. Execution Unit(EU)
In the EU we have some collection components.
They are:- 1. General Registers.
2. Execution Unit Control System.
3. ALU
4. Operands and Flags.

14. 1. General Registers
 In this we have two types of registers.
They are:- 1. Main Registers.
2. Index Registers.
Main Registers
AH AL AX(Primary accumulator)
BH BL BX(Base accumulator)
CH CL CX(Counter accumulator)
DH DL DX(accumulator other
funtions)

15. Index Registers
SP Stack Pointer
BP Base Pointer
SI Source Index
DI Destination Index

17. 2. Execution Unit Control System
In this unit the Execution is controlled and is
transferred to the all other components through the
internal data bus.
3. ALU(Arithmetic Logical Unit)
Here all the ALU operation are performed and
transferred the data through the internal data bus.

19. 4.Flags Registers
This flag is identical to 8085 flag register, with an
additional overflow flag, which is not present in 8085.
The 8086 has a 16-bit flag register which is divided into
two parts, viz.(a) condition code (or) status flags and (b)
machine control flags.
The condition code flag register is the lower byte of the
16-bit flag register along with the overflow flag.
 The machine control flag register is the higher byte of
the flag register of 8086 which contains three flags, viz.
direction flag(D), interrupt flag(I) and trap flag(T).

20. The bit configuration of 8086 flag
register.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
X X X X O D I T S Z X Ac X P X Cy
O – Overflow flag
D – Direction flag
I – Interrupt flag
T – Trap flag
S – Sign flag
Z – Zero flag
Ac – Auxillary carry flag
P – Parity flag
Cy – Carry flag
X – Not used (or) Future use

22. Memory Address and data bus interface
Address/Status
A16/S3
Address/Data
AD0/AD15
Instruction Queue (6 bytes)
Decoding circuit
Timing and control circuit
Clock and control signals
Address Adder
CS
DS
SS
ES
IP
ALU (16)
FLAGS (16)
15 0
AH AL
BH BL
CH CL
DH DL
IP
IP
IP
IP
AX
BX
CX
DX
Register Bank
B
I
U
E
U

23. Pin Diagram of
8086
Microprocessor