Case study: Alarm State Machine

Building the machine

One Flipflop per state

As we have three states, we must have the same number of flipflops (only one must be on at a time).

To have a simpler design, the input data and the state feedback are made available as a "bus" and the different gates just have to pick signals on it.

The logic is the direct application of the logic formulas.


12.Disarm + 3.Disarm + 1.Arm
21.Arm + 3.TimeOut + 2.(Disarm.Intrusion)
32.Intrusion + 3.(Disarm.TimeOut)



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Different components are added: a clock for the flipflops, a reset to set the initial state to the state "1", an oscillator to made the alarm blink and a counter to have some delay for the "TimeOut" signal".