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Execution Unit in 8086

de-multiplexer 8085
de-multiplexer 8085

The 8086 Processor is divided into two parts: Execution Unit and the Bus interface unit.

  • Functions of Execution Unit
  1. Control system inside the execution unit controls all internal and external operations by sending control signals. This results in fetching Instructions and Data from memory.
  2. It decodes and executes instructions fetched by Bus-Interface Unit.
  • Arithmetic and Logic Unit (ALU)
  1. The 16-bit ALU performing arithmetic operations and logical operations on 16-bit data operand.
  2. The ALU is capable of performing operations on 8-bit as well as 16-bit data operand.
  3. There are general-purpose register file in EU.
  • General Purpose registers
  1. AX, BX, CX, DX, SP, BP, SI and DI are the general purpose registers in Execution Unit.
  2. All registers are 16-bit long.  The AX, BX, CX and DX can be used in bytes as AH, AL, BH, BL, CH, CL, DH, and DL to hold 8-bit data.
  3. The AX register is an accumulator, the BX register hold address, the CX hold the count and DX holds data as well as IO address fro certain instructions.
  4. The SP- stack pointer, BP – base pointer, SI- source index and DI – destination index.

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