Asynchronous inputs

• Signals that change without concern for your clock

• Asynchronous inputs to synchronous circuits

  • Inputs will not meet flip-flop setup/hold times
  • Cannot avoid asynchronous inputs in real circuits
    • Reset signals
    • Memory wait
    • User input
    • RS-latch output

• Question: You build a custom board for a PCI slot. The board has a built-in 33MHz clock. The PCI clock is also 33MHz. The PCI bus sends data to your board. Is this a synchronous or an asynchronous interface?

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