Bus with four three-state drivers — buffer gate

Why this example is worth doing

Four drivers on one wire, with the invariant that at most one enable is asserted. Break it and two drivers fight — one pulling high, one pulling low — which is bus contention: a low-resistance path from supply to ground that can destroy the parts. The page frames it as a design rule with a physical consequence rather than a logic error, and notes that decoders exist largely to guarantee the one-hot enable pattern this needs.

Try your own input in the Buffer. Truth table, symbol and algebraic form for the non-inverting buffer, and what it is for.