8086 Microprocessor Features

Microprocessor (Definition re-visited): A Microprocessor (µp) is an Integrated Circuit with all the functions of a CPU. However, it cannot be used stand-alone since unlike a microcontroller it has no memory or peripherals.

• The Intel 8086 is a 16-bit microprocessor that was introduced in 1978 and played a major role in the development of personal computing.
• 8086 µp does not have a RAM or ROM inside it. However, it has internal registers for storing intermediate and final results and interfaces with memory located outside it through the System Bus.

The key features of the 8086 microprocessor are listed below:

Features of 8086 Microprocessor

Features of 8086 microprocessor are given below:

1. 16-bit Processor:

• The 8086 has a 16-bit data bus, which means it can process 16 bits of data at a time.
• It has a 16-bit arithmetic logic unit (ALU), registers, and an instruction set designed to handle 16-bit operations.

2. 20-bit Address Bus:

• The 8086 has a 20-bit address bus, allowing it to access up to 1 MB of memory (2²⁰ = 1,048,576 bytes or 1 MB).

3. Memory Segmentation:

• Memory is divided into segments to allow efficient management and utilization of the 1 MB address space. The four primary segments are:

a) Code Segment (CS): Contains the instructions to be executed.

b) Data Segment (DS): Contains data to be processed.

c) Stack Segment (SS): Contains data that supports subroutine calls, interrupts, and return values.

d) Extra Segment (ES): Used for additional data.

4. General Purpose Registers:

• There are eight 16-bit general-purpose registers, which can be used as 8-bit registers as well. These include:

a) AX (Accumulator Register)

b) BX (Base Register)

c) CX (Count Register)

d) DX (Data Register)

5. Instruction Set:

• The 8086 supports a rich instruction set, including arithmetic, logic, control, data transfer, and string manipulation instructions.
• It supports complex addressing modes, including direct, indirect, and relative addressing.

6. Queue (Prefetch):

• The 8086 has a 6-byte instruction queue that implements instruction pipelining, allowing it to fetch the next instructions while executing the current one, improving processing speed.

7. Interrupts:

• The processor supports hardware and software interrupts.
• There are 256 interrupt levels, and it can respond to both maskable and non-maskable interrupts (NMI).

8. Clock Speed:

• The 8086 typically operates at clock speeds ranging from 5 MHz to 10 MHz

9. Minimum and Maximum Modes:

• Minimum Mode: Used in single-processor systems. In this mode, the 8086 directly controls all the system’s operations.
• Maximum Mode: Used in multi-processor systems. In this mode, additional control is handed over to external hardware.

10. Addressing Modes:

• Supports several addressing modes including immediate, direct, register, indirect, and indexed addressing. These allow for flexible data handling.

11. Flags Register:

• The 8086 has a 16-bit flags register that reflects the outcome of operations. Flag register includes 6 status flag bits and 3 control flag bits.
• 6 status flag bits are listed below:

a) Zero Flag (ZF)

b) Carry Flag (CF)

c) Overflow Flag (OF)

d) Sign Flag (SF)

e) Parity Flag (PF)

f) Auxiliary Carry Flag (AF)

• 3 control flag bits are listed below:

a) Trap Flag (TF)

b) Instruction Flag (IF)

c) Direction Flag (DF)

12. Stack Operations:

• The 8086 supports efficient stack operations for subroutine calls and interrupt handling. The SP (Stack Pointer) and BP (Base Pointer) registers help in managing the stack.

13. Compatibility:

• The 8086 is compatible with its predecessors, such as the 8080 and 8085, making software migration relatively easy.
• These features made the 8086 an influential design in early computer systems and paved the way for future x86 architecture.