Microprocessor (Chapter-3)

8086 Architecture : The 8086 microprocessor is divided internally into two separate units. There are bus interface Unit (BIU) and the Execution Unit. The two units function independently. The BIU fetches instructions reads operands and writes results on the other hand the EU executes instructions that have already been fetched by the BIU

Executions Unit: The propose of execution unit (EU) is to execute instructions. It contains a circuit called the arithmetic and logic unit ALU. The ALU can perform arithmetic (+ - X /) and logic (and, or, xor) etc operations. The data for the operations are stored in circuits called registers. The EU has eight registers for storing data such as AX BX CX DX SI DI SP & BP.

Bus interface Unit: The BIU facilitates communication between the EU and the memory or I/O circuits. It is responsible for transmitting address. Data and control signals on the buses. It registers are named CS DS ES SS and IP. The BIU and EU are connected by an internal bus and they work together.

Real Mode Memory Addressing: The 80286 and above operate in either the real or protected mode. Only the 8086 and 8088 operate exclusively in the real mode. Real mode operation allows the microprocessor to address only the 1mb of memory space which is known as real memory or conventional memory.

8086 Addressing Mode: The 8086 has 12 addressing modes. These modes can be classified into five groups:

1. Resister and immediate modes

2. memory addressing modes

3. Port addressing mode

4. Relative addressing modes

5. Implied addressing modes