Missing Reset Causing Undefined State
A vending machine controller tracks inserted coins and asserts a dispense signal when enough credit is accumulated. The circuit receives a Reset signal and a Coin input, and should drive the Dispense output high after two consecutive coins are inserted.
Expected behavior:
| Reset | Coin | Current State | Next State | Dispense | |---------|--------|---------------|------------|------------| | 1 | 0 | Any | S0 | 0 | | 0 | 0 | S0 | S0 | 0 | | 0 | 1 | S0 | S1 | 0 | | 0 | 0 | S1 | S1 | 0 | | 0 | 1 | S1 | S2 | 1 | | 0 | 0 | S2 | S0 | 0 |
Simulation shows Dispense = X indefinitely at startup regardless of Coin inputs. The first test case outputs X instead of 0. Inspect the circuit and correct the fault.
Constraints
- Do not alter the combinational logic that calculates the next state.
- Do not add or remove any flip-flops.
Topics
Solve this problem
Place the gates, wire them up and watch the signals settle. Every submission runs on the same simulation engine that grades it.
This problem is part of Codiode Pro. The statement above is free to read.
The circuit builder and code editor need a desktop screen. On a phone, read the problem here and open it on a laptop to solve.