![]() ![]() Interesting fact: A true cycle-detection algorithm will theoretically let you simulate a whole CPU running any Turing-complete program, if you clock it with an "inherently unstable" ring oscillator. When you set that input back down, the NOR already has the other input high, so it doesn't change state and equilibrium is already reached.Ĭycle detection can be as simple as a hardcoded iteration count, or something a bit more accurate and useful: This doesn't change anything else, so the circuit reaches equilibrium. To use my example circuit, with both inputs low initially: when one of the inputs of one NOR is set high, in the next step the output goes low, then the other NOR's output goes high, and the input of the first NOR goes high. Also, we are going to use the 74LS00 IC chip to construct the derived NAND-based configurations on a. The three laws are explained in Figure 1. It is able to perform many different kinds of simulation (e.g. In order to construct NOT, AND, OR gates from NAND gates only, we need to be familiar with the following boolean algebra laws: 1. the output of each node can change at a different time relative to its input, so you process them in a queue ordered by that.) Qucs (speak: kju:ks) is a circuit simulator with graphical user interface. You can even add visualisations to show each step of the propagation as it takes place, and more elaborate versions can take into account different propagation delays (i.e. The above algorithm reasonably accurately models what happens in a real digital circuit: changes propagate through each node until the whole circuit reaches a steady state. The general idea is to iterate while changes are still propagating through the circuit here's some pseudocode: ![]() the two NORs essentially become inverters when one of their inputs is 0, and they act in positive feedback to hold the bit value why almost every other diagram insists on crossing the wires is perplexing, since it only serves to confuse and complicate.Īs for designing the simulator engine to solve these kind of cyclic circuits, and advice on how to do it? 25 Multiple input gates (three or more inputs) of types nand and nor failed at. The circuit uses two NAND gates set up as a latch that is being set or. If the signal wires are not named by the user, Qucs will allocate them. Also, as another minor tangent, I think the flip-flop is so much easier to understand when it's drawn to emphasise the storage loop, i.e. In this circuit the duty cycle of the output square wave is not exactly 50 i. IMHO having trouble with something like that means the simulation engine is not quite usable yet.Įdit: the above circuit works fine in Logisim. I even tried "bootstrapping" the circuit by breaking the storage loop and setting the two gates' inputs so they're all consistent first before connecting them together, but then when I disconnect the bootstraps it immediately returns to the above arrangement. The gates themselves in isolation work fine, but connecting them together doesn't. It looks nice and easy to use but I can't seem to get something as basic as a two-NOR flip-flop to work: ![]()
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