The 80286 Microprocessor Architecture & Features

80286 Microprocessor Architecture & Features – The 80286 microprocessor, with its 24-bit address bus, is able to address 16M byte of physical memory. The 80286 microprocessor is an advanced version of the 8086 microprocessor in terms of enhanced hardware and instruction set.

Architecture of 80286 Microprocessor

The block diagram of the 80286 microprocessor architecture is shown in Figure 1. The 80286 microprocessor hardware is internally divided into four functional units.

1. Address Unit (AU)
2. Bus Unit (BU)
3. Instruction Unit
4. Execution Unit

Address Unit (AU)

The address unit computes the physical address of the instructions and data to be accessed by the microprocessor. Address lines of this unit may be used to address other peripherals.

Bus Unit (BU)

The physical address computed by the AU is handed over to the bus unit. This physical address is transmitted to the address bus (A₀ – A₂₃) by this unit. The major function of the bus unit is to fetch instruction bytes from memory and store them in its predefined queue. This is known as instruction pipelining.

Instruction Unit (IU)

The instruction unit accepts instructions from the perfected queue, and an instruction decoder decodes them one by one. The decoded instructions are stored in a decoded instruction queue.

Execution Unit (EU)

The primary function of the execution unit is to execute the instructions received from the decoded instruction queue. The EU carries out all the arithmetic and logical operations and sends the results either over the data bus or back to the register bank.

Features of the 80286 Microprocessor

The 80286 microprocessor is a 16-bit microprocessor and has the following salient features.

1. The 80286 microprocessor is the first microprocessor to incorporate the integrated memory management unit.
2. The 80286 microprocessor addresses 16M byte of physical memory and 1G bytes of virtual memory by using its memory management system.
3. Data protection or unauthorized access prevention is provided with the concept of segmented memory.
4. It works in two operating modes via read address mode and protected virtual address mode. In real address mode, it acts as a fast 8086. In protected virtual address mode, it works with all of its memory management and protection capabilities.

At this time, the 80286 microprocessor no longer has a place in personal computers (PCs) but is used in control systems as an embedded controller.