Combinational versus sequential logic

B

A

C

Clock

• Combinational means memoryless

  • Outputs depend only on the present inputs
    • Apply fixed inputs A, B
    • Wait for clock edge
    • Observe C
    • Wait for another clock edge
    • Observe C again: C will stay the same

• Sequential systems have memory

  • Outputs depend on the present inputs and on the previous inputs
    • Apply fixed inputs A, B
    • Wait for clock edge
    • Observe C
    • Wait for another clock edge
    • Observe C again: C may be different

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