Async Input Without Synchronizer: Direct DFF Connection
An asynchronous input fed directly into a positive-edge-triggered D flip-flop causes metastability if it transitions simultaneously with the clock edge. Five signals are shown: CLK (clock, period 2), D (asynchronous input), B (synchronous combinational input), Q (flip-flop output, initially 0), and OUT (combinational output of Q AND B). Trace both Q and OUT across all 10 time steps. Use the value X to denote any metastable or indeterminate state.
Constraints
Qevaluates toXifDchanges at the exact time step of a rising clock edge.OUTevaluates toXonly if the indeterminate state cannot be resolved by the known inputB.
Topics
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