8-bit microprocessors are limited in their speed (the number of instructions that can be executed in 1 s), directly addressable memory, data handling capability, and so forth. Innovations in semiconductor technology have made it possible for the manufacturers to develop 16-bit, 32-bit, 64-bit and even larger-bit microprocessors. In this article, we look at the main features of Intel 8086 microprocessor.
The Intel 8086 also referred to as iAPX86 is a 16-bit microprocessor introduced by Intel in the year 1976. It was designed using HMOS technology and contains approximately 29000 transistors. It has a maximum operating frequency of 10 MHz. The 8086, 8088, 80186 and 80286 microprocessors have the same basic set of registers and addressing modes. The 8086 microprocessor is available in DIP, CerDIP, and PLCC packages.
Related: Basic Architecture of a Microprocessor
A block diagram of the 8086 is shown below:
Contents
8086 Registers
8086 microprocessor has four segment registers and other general-purpose registers.
The segment registers include:
- Code segment (CS)
- Stack segment (SS)
- Data segment (DS)
- Extra segment (ES)
The general-purpose registers of 8086 microprocessor include:
- Accumulator register
- Base register
- Count register
- Data register
- Stack pointer (SP)
- Base pointer (BP)
- Source index (SI)
- Destination index (DI)
The stack pointer, base pointer, source index and destination index registers are both general and index registers. Other registers include the instruction pointer (IP) and the flag register containing nine 1-bit flags.
Addressing Modes of 8086 Microprocessor
The addressing modes of 8086 include:
- Implied addressing
- Register addressing
- Immediate addressing
- Direct addressing
- Register indirect addressing
- Base addressing
- Indexed addressing
- Base indexed addressing
- Base indexed with displacement addressing.
Related: 6 Types of Microprocessor Addressing Modes
Internal Architecture and Pin-out Configuration
The internal functions of the 8086 processor are portioned logically into two processing units as illustrated in the block diagram in Figure 1.0 above:
- Bus interface unit (BIU)
- Execution unit (EU)
The bus interface unit provides the functions related to instruction of fetching and queuing, operand fetch and store and address relocation. It also provides the basic bus control.
The execution unit receives pre-fetched instructions from the BIU queue and provides un-relocated operand addresses to the BIU.
Instruction Set
The 8086 instruction set includes:
- Data transfer operations
- Arithmetic operations
- Logical instructions
- String manipulation instructions
- Control transfer instructions
- Processor control instructions
- Input/output operations
Related articles:
- Basic Microprocessor Instructions
- Peripheral Devices used with Microprocessors
- The Intel 8085 Microprocessor
- RISC vs. CISC Processors
- The Pentium Series of Microprocessors
- Basic Features of 68HC11 Family of Microcontrollers
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