Cross-coupled NOR latch, both inputs 0 — circuit to expression
coreno combinational expression: state is held
Answer
cycle detected — no combinational expression (q → qn → q)
A cyclic netlist stores state. Its output depends on its own history, so no combinational expression describes it.
Why this example is worth doing
The circuit that breaks the tool, deliberately. Two NOR gates each feeding the other's input form a loop, and a loop has no combinational expression at all — the output depends on history, not just on the current inputs. The reader detects the cycle and says so rather than diverging or emitting nonsense, then sends the reader to the flip-flops page for the characteristic-equation treatment. Knowing when a question is not a combinational question is the actual lesson.
Try your own input in the Logic circuit → expression. Wire up gates and read the Boolean expression and truth table back out.
How the answer is reached
Gate list
| Node | Gate | Inputs |
|---|---|---|
| q | nor | R, qn |
| qn | nor | S, q |
Feedback loop
Combinational feedback loop: q → qn → q. Sequential logic is not supported.