Day 3: Pre-Class Self-Check Quiz

Procedural Combinational Logic

Q1: Why must you use @(*) instead of a manual sensitivity list?

Answer

Manual lists risk sim/synth mismatch. If you forget a signal, simulation won't update when it changes, but synthesis will. @(*) automatically includes all signals read inside the block.

Q2: What causes an unintentional latch? Give an example.

Answer

Not assigning a signal in every possible path through always @(*). Example: if (sel) y = a; with no else — when sel=0, y must hold its value → latch inferred.

Q3: Name three techniques to prevent latch inference.

Answer

1. Default assignment at the top of the block
2. Complete if/else chains (always have an else)
3. default case in case statements

Q4: When do you use = vs <=?

Answer

= (blocking) for combinational always @(*). <= (nonblocking) for sequential always @(posedge clk). Never mix them in the same block.