Specification

1.: The reaction timer will have a READY/RESET pushbutton (debounced). In one state the system is reset. When reset, upon activation of READY/RESET the system will initiate the reaction testing process. On completion of the testing process (either normally with the time display, or abnormally with CHEAT status), activation of READY/RESET causes the system to return to the reset state.
2.: At a random time between 1 and 9 seconds after READY is asserted, the GO! led is asserted, signaling the start of the reaction timing. The random time before the assertion of GO! removes the possibility of anticipating the start of the timing period.
3.: A pushbutton STOP switch is depressed to end the reaction time measurement by stopping the timing process.
4.: The reaction time t_r (0.XY seconds) is displayed by two 7-segment displays. The error should be less than $\pm 0.02$ seconds, and the reaction time is timed up to a maximum of t_r = 0.99 seconds (a reaction time of more than 0.99 seconds will be displayed as 0.99 seconds and the timing process halted).
5.: If the STOP button is depressed before the GO! led is asserted, a CHEAT led should be asserted and the testing process halted.
6.: The 7-segment displays should be blanked until a valid measurement is complete.

A block diagram of the reaction timer is shown in Figure 52.¹ Your task is to design the circuitry for each module shown, using the systematic design methods you have learned in this course. In particular, you are to design the FSM controller which controls the overall operation.

**Figure 52:** Reaction timer block diagram.
$\begin{figure} \par\centerline{\psfig{figure=images/block.eps}} \par\end{figure}$

The following notes describe the function of each module and give suggestions for implementation.

Controller FSM. The controller is to be a synchronous sequential FSM. The clock frequency is 1kHz. It receives input signals (debounced) READY/RESET and STOP, signals from other modules, and issues signals to other modules. Also, the controller should automatically reset on power-up (SANITY).
Timer. The timer generates the random time interval of between 1 and 9 seconds and is responsible for reaction time measurement. This later requirement involves a count sequence $0.00, 0.01, \ldots, 0.99$ seconds. It is a synchronous sequential machine.
Display. The display module consists of two 7-segment displays for displaying the reaction time, and two leds for GO! and CHEAT. The display should be blanked on reset.

The two pushbuttons on the digital trainer board are debounced.

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