8086 microprocessor | Operation modes | Features

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8086 microprocessor is a 16 bit chip designed by Intel in 1976. It is just an enhanced version of 8085 which is an 8-bit microprocessor. Comparing to 8085 8086 consists of a powerful instruction set. Later in this article we will discuss about different types of instruction sets and their operations that 8086 microprocessor offers. In this article we will discuss about the internal architecture such as operation modes and features of the 8086 microprocessor.

Features Of 8086 Microprocessor

The feature of 8086 microprocessor includes:

  • It is a 40 pin integrated circuit (IC). Means the 8086 chip consists of 40 pins and each pin having separate function.
  • It is a 16-bit processor, means it can process 16 bit data at a time
  • Its operating voltage is 5 volts. To perform any operation the microprocessor requires 5 volts power supply.
  • The processor’s operating frequency is 5 MHz.
  • It can hold total addressing capacity of 1 Megabyte.
  • The bus size of 8086 includes it has 16 bit data bus and 20 bit address bus. 16 bit of data can travel on the bus at a time and the address bus can handle 20-bit of data at a time.
  • It also has fourteen 16-bit register. So it has 14 registers and each register is 16 bit size.
  • It can support higher throughput comparing to 8085 microprocessor.

Intel 8086 pinout.svg
8086 Microprocessor is 40 pin Integrated Circuit (IC)

Operation Modes of 8086

Now let see the operation modes of 8086 microprocessor. 8086 can operate in two modes:

  • Maximum Mode also calls it as MAX Mode, and the
  • Minimum Mode or MIN Mode

Operation in MAX mode means it supports multi-processors system. Hence it can operate with more than one processor. So in this system processor can handover its work to some other components those can act like processor. Whenever so many instructions need to be executed at that time processor can handover the system bus to some other components. Similar to DMA (Direct Memory Access) which can access the processor means it can send the data directly to the i/o devices and to the memory without CPU involvement. So here DMA can act like a processor. Because it is doing the operation of the processor, not the arithmetic operation only the transferring operation. Hence the system efficiency increases.

Operation in Minimum mode means it is just a single processor system. Only one processor which can perform all the operation. So when ever the system has single processor we can call it as minimum mode.

Pin Diagram of 8086

The pin diagram of 8086 we have seen above is a 40 pins Dual Inline Package (DIP) which was a first 16 bit microprocessor available in 40 pin DIP.

As we can see that one side of the chip is 1 to 20 pins and another side 21 to 40 pin connected. Each pin having the specific function. Here the first pin is Ground and pin 2 to 16th pin is Multiplex address and data bus, AD0 to AD14. Including the 39th pin AD15 is also the Multiplex. Because 8086 support 16 bit data bus and 20 bit address bus. Therefore the remaining 4 pins pin35 to 38 is only the address bus which are D-multiplex. These 4 pins are also used as status signal. Pin no 34 is BHE or Bus High Enable also used as no 5th status signal. The main use of BHE is, it distinguishes between the low byte and high byte of 16 bit external data bus of 8086.

Internal Architecture of 8086

Internal architecture of 8086 consists of two main functional units. Those are:
Bus Interface Unit, and
Execution Unit

BIU or Bus Interface Unit act as a mediator between I/O devices and the processor. On the other hand the Execution Unit (EU) execute the information from the user.

In the next two separate article we discuss about the function of BIU and EU in more details

Read more articles on similar topic here.

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