How to simulate circuit of logic gates and flipflops

Question

I'm currently learning C# and WPF, and i'm trying to simulate a circuit of logic gates and flipflops, but it won't work.

Could someone please show me a possible way to achive this? (maybe a simple similar application?)

What i have tried so far:

---

Class:

    public class GateBase
    {
        public Type Type { get; set; }
        public GateBase Input1 { get; set; }
        public GateBase Input2 { get; set; }
        public List<GateBase> Outputs { get; set; }
        public bool Evaluated { get; set; }
        public bool Value { get; set; }
        public bool FlipFlop { get; set; }

        public GateBase(Type type = Type.OFF, Gate input1 = null, Gate input2 = null)
        {
            Type = type;
            Input1 = input1;
            Input2 = input2;
            Outputs = new List<GateBase>();
            Evaluated = false;
            Value = false;
            

            FlipFlop = false;

            switch (Type)
            {
                case Type.T:
                case Type.D:
                case Type.SR:
                case Type.JK: FlipFlop = true; break;
            }
        }

        public bool Evaluate()
        {
            if (!Evaluated)
            {
                bool input1 = false;
                bool input2 = false;

                if (Input1 != null)
                {
                    if (Input1.FlipFlop)
                        input1 = Input1.Value;
                    else
                        input1 = Input1.Evaluate();
                }

                if (Input2 != null)
                {
                    if (Input2.FlipFlop)
                        input2 = Input2.Value;
                    else
                        input2 = Input2.Evaluate();
                }

                switch (Type)
                {
                    case Type.OFF:
                        Value = false; break;
                    case Type.ON:
                        Value = true; break;
                    case Type.OUT:
                        Value = input1; break;
                    case Type.CON:
                        Value = input1; break;
                    case Type.NOT:
                        Value = input1; break;
                    case Type.AND:
                        Value = input1 & input2; break;
                    case Type.OR:
                        Value = input1 | input2; break;
                    case Type.XOR:
                        Value = input1 ^ input2; break;
                    case Type.NAND:
                        Value = !(input1 & input2); break;
                    case Type.NOR:
                        Value = !(input1 | input2); break;
                    case Type.XNOR:
                        Value = !(input1 ^ input2); break;
                    case Type.D:
                        Value = input1; break;
                    case Type.T:
                        Value = input1 ? Value : !Value; break;
                    case Type.SR:
                        Value = (input1 ^ input2) ? Value : Value; break;
                    case Type.JK:
                        Value = (input1 ^ input2) ? input1 : (input1 & input2) ? !Value : Value; break;
                    default: Value = false; break;
                }
            }
            Evaluated = true;
            return Value;
        }

        public void ResetOutputs()
        {
            Evaluated = false;
            foreach (Gate gate in Outputs)
            {
                if(!gate.FlipFlop)
                {
                    gate.ResetOutputs();
                }
            }
        }
    }

Loop:

• Update all logic gates
• Update all flipflops and unevaluate outputs of each flipflop (if they are not a flipflop)

     public List<GateBase> Gates { get; set; }

     while (loop)
            {
                bool evaluating = true;
                while (evaluating)
                {
                    evaluating = false;
                    foreach (Gate gate in Gates)
                    {
                        switch (gate.Type)
                        {
                            case Model.Type.ON:
                            case Model.Type.OFF:
                                gate.Value = gate.Evaluate();
                                break;
                            case Model.Type.OUT:
                            case Model.Type.CON:
                            case Model.Type.NOT:
                                if (gate.Input1 != null && (gate.Input1.Evaluated || gate.Input1.FlipFlop))
                                {
                                    gate.Value = gate.Evaluate();
                                }
                                break;
                            case Model.Type.AND:
                            case Model.Type.OR:
                            case Model.Type.XOR:
                            case Model.Type.NAND:
                            case Model.Type.NOR:
                            case Model.Type.XNOR:
                                if (gate.Input1 != null && gate.Input2 != null)
                                {
                                    if ((gate.Input1.Evaluated || gate.Input1.FlipFlop) && (gate.Input2.Evaluated || gate.Input2.FlipFlop))
                                    {
                                        gate.Value = gate.Evaluate();
                                    }
                                }
                                else
                                {
                                    evaluating = true;
                                }
                                break;
                        }
                    }
                }

                evaluating = true;
                while (evaluating)
                {
                    evaluating = false;
                    foreach (Gate gate in Gates)
                    {
                        switch (gate.Type)
                        {
                            case Model.Type.D:
                            case Model.Type.T:
                                if (gate.Input1 != null && (gate.Input1.Evaluated || gate.Input1.FlipFlop))
                                {
                                    gate.Value = gate.Evaluate();
                                    gate.ResetOutputs();
                                }
                                else
                                {
                                    evaluating = true;
                                }
                                break;
                            case Model.Type.SR:
                            case Model.Type.JK:
                                if (gate.Input1 != null && gate.Input2 != null)
                                {
                                    if ((gate.Input1.Evaluated || gate.Input1.FlipFlop) && (gate.Input2.Evaluated || gate.Input2.FlipFlop))
                                    {
                                        gate.Value = gate.Evaluate();
                                        gate.ResetOutputs();
                                    }
                                }
                                else
                                {
                                    evaluating = true;
                                }
                                break;

                        }
                    }
                }
            }

Problem:

If i'm using the JK-flipflop the results are not as expected. (but the T-flipflop works fine)

---

Here a link to the solution: Solution on GitHub

Thank You!

Answer 1

You have no break for your switch cases inside the while loop, so if the case is Model.Type.AND it will fall all the way down to the Model.Type.XNOR and I assume this isn't intended. This might be your problem (or at least a part of it).

Just to give you an idea, this small example will output "no break". x = 3 will output the string from default.

using System;

public class Program
{
    public static void Main()
    {
        int x = 1;
        switch(x){
            case 0:
                Console.WriteLine("Break");
                break;
            case 1:
            case 2:
                Console.WriteLine("no break");
                break;
            case 3:
            default:
                Console.WriteLine("End!");
                break;
        }
    }
}

You can read more about the traditional switch here: switch C# reference from Micrsoft

Answer 2

Now i fixed a problem and it's working much better than before. (i was resetting the gates before all flipflops were updated)

But it's still not working 100% correct...

Changes in the Loop:

// new list
List<Gate> gatesToResetOutputs = new List<Gate>();

while(loop)
{
    while(evaluating gates)
    {
        ...
    }

    while(evaluating flipflops)
    {
        ...
        // instead of
        gate.ResetOutputs();
    
        // replace with
        gatesToResetOutputs.Add(gate);
        ...
    }

    // and at the end of the loop
    foreach(Gate gate in gatesToResetOutputs)
    {
        gate.ResetOutputs();
    }
}