Hack to allow single step tests to completely work: disable IO area triggers.

LR35902/Bus.cs

@@ -37,9 +37,9 @@ namespace LR35902
 
         private int allowed = 0;
 
-        protected Bus()
+        protected Bus(bool ioTriggers = true)
         {
-            this.IO = new IoRegisters(this);
+            this.IO = new IoRegisters(this, ioTriggers);
             this.CPU = new LR35902(this);
             this.CPU.MachineTicked += this.CPU_MachineTicked;
             this.WrittenByte += this.Bus_WrittenByte;

LR35902/IoRegisters.cs

@@ -90,12 +90,15 @@ namespace LR35902
         private bool p11 = true;  // left/b
         private bool p10 = true;  // right/a
 
-        public IoRegisters(Bus bus)
+        public IoRegisters(Bus bus, bool triggered = true)
         : base(0x80)
         {
             this.bus = bus;
-            this.bus.ReadingByte += this.Bus_ReadingByte;
-            this.bus.WrittenByte += this.Bus_WrittenByte;
+            if (triggered)
+            {
+                this.bus.ReadingByte += this.Bus_ReadingByte;
+                this.bus.WrittenByte += this.Bus_WrittenByte;
+            }
         }
 
         public event EventHandler<LcdStatusModeEventArgs>? DisplayStatusModeUpdated;

LR35902/SM83.HarteTest/TestRunner.cs

@@ -9,6 +9,7 @@
         public Ram RAM { get; } = new(0x10000);
 
         public TestRunner()
+            : base(false)
         {
             this._mapping = new(this.RAM, 0x0000, (ushort)Mask.Sixteen, AccessLevel.ReadWrite);
         }