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8085 Bus Organization

The operation of a microprocessor unit includes,

  • Memory Read.
  • Memory Write.
  • I/O Read.
  • I/O Write.

Communication of a Microprocessor unit with peripheral devices involves,

  1. Identify peripheral or memory location.
  2. Transfer data and instruction.
  3. Provide timing and synchronization signals.

The microprocessor uses three sets of communication lines called buses to perform these functions. A bus is a collection of lines, which perform the same logical task. The 8085 bus organization is shown in the figure.

8085 bus organization
8085 Bus Organization

Address Bus

  • Group of 16 bits from A0 to A15.
  • Carries the address of a particular location.
  • Unidirectional– Data flows from microprocessor to peripheral devices only.
  • Function– To identify a peripheral or a memory location.
  • Capable of addressing 65536(216) memory locations. (Generally 64K)


  • Group of 8 lines used for data flow.
  • Carries the data to be transfered.
  • Bidirectional– Data flow in both direction between the microprocessor and memory / peripheral devices.
  • Function– To transfer binary data and instruction.
  • Enable the microprocessor to manipulate 8-bit data ranging from 00 to FF. (28=255)

Control Bus

  • Group of various single lines that carry control signals.
  • Microprocessor generate specific control signals for every operation.
  • Function– To provide timing and synchronization signals.
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