mpmc microprocessor
DESCRIPTION
About MicroprocessorTRANSCRIPT
ARCHITECTURE OF
8086
MICROPROCESSOR
By
A.S.Krishna
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.
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.
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.,
Architecture of 8086
BIU(Bus Interface
Unit)
EU(Execution Unit)
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
1. Address Adder
In the address adder the adder adds the addresses and transfer them to the memory though the internal data bus path.
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
3. Instruction Queue
Instruction Queue 6
5
4
3
2
1
This a Queue which can store the given instructions one-by-one.
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.
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)
Index Registers
SP Stack Pointer
BP Base Pointer
SI Source Index
DI Destination Index
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.
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).
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 CyO – Overflow flag
D – Direction flagI – Interrupt flagT – Trap flagS – Sign flagZ – Zero flagAc – Auxillary carry flagP – Parity flagCy – Carry flagX – Not used (or) Future use
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) IP IP IP
IP
AH ALBH BLCH CLDH DL
15 0
AX
BX
CX
DX
Register Bank
B
I
U
E
U
Pin Diagram of 8086 Microprocessor
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