Jeopardy Buttons

• Problem: There are two buttons.
• The first button pushed illuminates the corresponding LED.
• Any further pushes are ignored.
• The LED's can be reset by the ``game master'' (Alex).
• Considerations: The objective is to switch the LED's on.
• Thus, the output Q of the flipflops are to be switched into the 1 state.
• Therefore, the D inputs should be 1 when the buttons are pushed, i.e., we may connect the buttons to the D inputs of the flipflops.
• The updating of the flipflops is controlled through the Enable inputs.
• The following conditions must be met to allow a transition from 0 to 1 for either flipflop:
  • The corresponding button must be pushed, and
  • Neither of the two flipflops is currently in the 1 state, i.e., no button has been pushed before.
• This sugests that we construct a ``Lock'' signal by NOR-ing the two flipflop outputs.
• The Lock Signal is then AND-ed with the signal from the switches and connected to the Enable input of the flipflop.
• Then, the Enable input can go to one only if the Lock signal is 1 (both flipflops are in the 0 state) and the button is pushed.
• The game master's button is connected to the reset input of the flipflops, such that both flipflops return to the 0 state when that button is pushed.