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Let's assume we have the Truth Table for our Finite state machine.

How can we determine the maximum clock frequency for the system, under the assumptions that the wire delay is 0.3 ns , flip-flop setup time is 0.2 ns, and gate delays are 0.4 ns for 2-input gates and 0.5 ns for gates with more than 2 inputs.

Firstly I should find boolean function for each output, outputs to real world and outputs for next states to controller I guess. Then what?

Thanks in advance, btw this is my first question in electronics :)

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Timing is fully dependant on the implementation. You will need to fully specify all the state equations, transition equations and output equations. Then you go through a minimization process to reduce the equations to a minimal set. After that you can map your standard gate and flip-flop selections to the sets of logic equations. Once you compute the worst case timing condition that will lead directly to the maximum clock frequency. Sounds like you know where to start. There is some work to do before you can start throwing around timing numbers.

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for a back of the envelope calculation/reality check.

Assumption, FF-> one layer of logic -> FF and fully synchronous. - delay + wire delay + SU = 0.5 + 0.3 +0.2 = 1 ns. -> Clock at 1 GHZ.

drive to outside world will be slower (bigger transistors, more loading) drive to other gates will depend upon fan in and your gate's drive capability.

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  • \$\begingroup\$ Even in the simple reality check you need to consider at least two wire delays because there is wiring from FF->Logic and then another wiring delay from Logic->FF. \$\endgroup\$ – Michael Karas Jan 10 '13 at 12:10

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