Add motherboard tests, especially power-on reset circuit tests

EightBit/Bus.cs

@@ -7,7 +7,7 @@ using System.Runtime.CompilerServices;
 
 namespace EightBit
 {
-    public abstract class Bus : IMapper
+    public abstract class Bus : Device, IMapper
     {
         private bool _writing;
         private byte _data;
@@ -54,16 +54,6 @@ namespace EightBit
             Debug.Assert(!this._writing, "Writing flag is in an invalid state");
         }
 
-
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1030:Use events where appropriate", Justification = "The word 'raise' is used in an electrical sense")]
-        public virtual void RaisePOWER()
-        {
-        }
-
-        public virtual void LowerPOWER()
-        {
-        }
-
         public abstract void Initialize();
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]

EightBit/Processor.cs

@@ -55,7 +55,7 @@ namespace EightBit
 
         public Register16 Intermediate { get; } = new();
 
-        protected byte OpCode { get; set; }
+        public byte OpCode { get; protected set; }
 
         // http://graphics.stanford.edu/~seander/bithacks.html#FixedSignExtend
         public static sbyte SignExtend(int b, byte x)