Archive for January 2012

Flag Registers In 8086, Conditional flag,

The Conditional Flag:-

There are six conditional flag.

  1. The Parity Flag(PF)
  2. The Zero Flag(ZF)
  3. The Sign Flag(SF)

Flag Registers In 8086

      Flag Register:- 

      It is a 16-bit register with each bit corresponding to a flip-flop. It changes its status according to the stored output in the accumulator. A flag can control certain operation of the EU.

The Execution Unit, EU

The execution unit(EU):

The main function of EU is decoding and execution of the instructions. It tells the BIU that where to fetch instructions or data from.

Different Parts of Execution Unit(EU):-

Bus Interface Unit, BIU, __Continue........

Instruction Pointer:-
      It is 16-bit register, which identifies the location of the next word of instruction code that is to be fetched in the current code segment.
      IP contains an offset instead of the actual address of the next instruction.
      The 20-bit address produced after addition of the offset stored in IP to segment base address in the CS is called the Physical address of the code byte.

Bus Interface Unit, BIU

The Bus Interface unit (BIU)

This unit handles all transfer of data and addresses on the buses for the EU(execution unit). This unit sends out addresses, fetches instructions from memory, reads data from ports and memory and writes data to ports and memory.

Different Parts of BIU:
a.Segment Register

8086 Internal Architechture


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