Internal architecture of Intel 8086 microprocessor

Last updated on June 13th, 2020 at 08:32 pm

The Intel 8086 is a 16-bit microprocessor designed by Intel corporation between 1976-1978. It is also called the iAPX 86. This Intel 8086 microprocessor gave rise to the x86 architecture or 16-bit architecture. Following figure is the internal architecture of Intel 8086 microprocessor

Features of 8086 Microprocessor:

  1. 8086 includes an Instruction Queue. While an instruction is getting executed, it can store 6 instructions bytes at most at a time. It improves the performance.
  2. The 8086 microprocessor has registers, internal and external buses and ALU, all of 16-bit. As a result it performs faster operations.
  3. Microprocessor 8086 can simultaneously execute an instruction and fetch the next one.

Intel 8086 microprocessor has two units; Execution Unit (EU) and Bus Interface Unit (BIU). These 2 units depends on each other to function.

Units and Registers of 8086 Microprocessor:

Execution Unit (EU):

Execution unit receives program instruction codes and data from the BIU. Then it executes those and stores the result in the general registers. It can also store the data in a memory location or send them to an I/O device using the BIU. This unit, EU, has no connection with the system Buses. It receives and outputs all its data through BIU.

Bus Interface Unit:

Bus Interface Unit has connection with the system busses. BIU and EU are connected with an internal bus. BIU connects EU with the memory or I/O circuits. It is responsible for transmitting data, addresses and control signal on the buses.

General Registers:

General Registers or General Purpose Registers can store both data and addresses. All general registers of the Intel 8086 microprocessor can be used for arithmetic and logic operations. In the above given figure of Intel 8086 microprocessor, all data, pointer and index registers are general registers.

Segment Registers:

There are four segment registers, CS (Code Segment), DS (Data Segment), ES (Extra Segment) and SS (Stack Segment).

Instruction Pointer (IP):

To access instructions, the Intel 8086 uses the CS and IP registers. The CS register contains the segment number of the next instruction, while the IP contains the offset. IP is updated each time an instruction is executed. As a result, it will then point to the next instruction. Unlike other, instructions can not directly manipulate the IP register. Thus an instruction may not contain IP as its operand.

Flag Registers:

Intel 8086 has 16 flag registers among which 9 are active. The purpose of the flag register is to indicate various statuses of the processor. It does this by setting the individual bits called flags. There are two kind of flag registers; status flag register and control flag register. Status flag register reflect the result of an operation executed by the processor. On the other hand, the control flag registers enable or disable certain operations of the processor. The 9 active flag registers are Carry Flag (CF), Parity Flag (PF), Auxiliary Flag (AF), Zero Flag (ZF), Sign Flag (SF), Trap Flag (TF), Interrupt Flag (IF), Direction Flag (DF) and Overflow Flag (OF).

Arithmetic and Logic Unit (ALU):

Arithmetic and Logic Unit is a like a calculator. ALU performs all arithmetic operations along with decision making functions. In modern CPU or Microprocessors, there can be more than one integrated ALU to speed up arithmetical and logical operations, such as; integer unit, floating point unit etc.

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