8086 MICROPROCESSOR
Features of 8086
16-bit general purpose microprocessor.
16-bit data bus.
20-bit address bus, which can address up to 220 memory locations (1 MB).
It can support up to 64K I/O ports.
40 pin dual in line package.
Requires +5 V power supply.
Clock frequency changes between 5 MHz, 8 MHz, 10 MHz depending on the version.
Comparison between 8085 & 8086 Microprocessor
Sl No 8085 Microprocessor 8086 Microprocessor
1. 8-bit microprocessor 16-bit microprocessor
2. 8-bit data bus 16-bit data bus
3. 16-bit address bus 20-bit address bus
4. Can access up to 64KB of memory Can access up to 1 MB of memory
5. Does not support pipelining Supports pipelining
6. Less expensive More expensive
8086 microprocessor Architecture
8086 CPU is divided into two independent functional parts
1. Bus Interface Unit (BIU) 2. Execution Unit (EU)
o Instruction queue o Control circuitry
o Segment registers o Instruction decoder
o Instruction pointer o ALU
o Address adder o Pointer and Index register
o Flag register
1
, Bus Interface Unit (BIU):
The BIU sends out addresses, fetches instructions from memory, reads data from ports and
memory, and writes data to ports and memory.
The BIU handles all transfers of data and addresses on the buses for the execution unit.
Execution Unit (EU)
The main functions of EU are:
o Decoding of instructions
o Execution of instructions
Steps
o EU extracts instructions from top of queue in BIU
o Decode the instructions
o Generates operands if necessary
o Passes operands to BIU & requests it to perform read or write bus cycles to memory or I/O
o Perform the operation specified by the instruction on operands
2
Features of 8086
16-bit general purpose microprocessor.
16-bit data bus.
20-bit address bus, which can address up to 220 memory locations (1 MB).
It can support up to 64K I/O ports.
40 pin dual in line package.
Requires +5 V power supply.
Clock frequency changes between 5 MHz, 8 MHz, 10 MHz depending on the version.
Comparison between 8085 & 8086 Microprocessor
Sl No 8085 Microprocessor 8086 Microprocessor
1. 8-bit microprocessor 16-bit microprocessor
2. 8-bit data bus 16-bit data bus
3. 16-bit address bus 20-bit address bus
4. Can access up to 64KB of memory Can access up to 1 MB of memory
5. Does not support pipelining Supports pipelining
6. Less expensive More expensive
8086 microprocessor Architecture
8086 CPU is divided into two independent functional parts
1. Bus Interface Unit (BIU) 2. Execution Unit (EU)
o Instruction queue o Control circuitry
o Segment registers o Instruction decoder
o Instruction pointer o ALU
o Address adder o Pointer and Index register
o Flag register
1
, Bus Interface Unit (BIU):
The BIU sends out addresses, fetches instructions from memory, reads data from ports and
memory, and writes data to ports and memory.
The BIU handles all transfers of data and addresses on the buses for the execution unit.
Execution Unit (EU)
The main functions of EU are:
o Decoding of instructions
o Execution of instructions
Steps
o EU extracts instructions from top of queue in BIU
o Decode the instructions
o Generates operands if necessary
o Passes operands to BIU & requests it to perform read or write bus cycles to memory or I/O
o Perform the operation specified by the instruction on operands
2
