Some minor changes and playing about

Core/Io/IO_Bus.cs

@@ -0,0 +1,43 @@
+using System.Diagnostics;
+using Core.Interfaces;
+
+namespace Core.Io
+{
+    public class IO_Bus
+{
+    // 8 rows representing the Spectrum keyboard matrix. Default to 0xFF (unpressed).
+    public byte[] KeyboardRows = new byte[8] { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
+
+    public byte ReadPort(ushort portAddress)
+    {
+        // The Spectrum ULA responds to any even port address (where the lowest bit is 0)
+        if ((portAddress & 0x01) == 0)
+        {
+            byte highByte = (byte)(portAddress >> 8); // The B register!
+            byte result = 0xFF; // Start assuming no keys are pressed
+
+            // The ROM pulls a specific bit low (0) in the high byte to request a row.
+            // Sometimes it pulls multiple bits low to scan multiple rows at once, so we AND the results.
+            if ((highByte & 0x01) == 0) result &= KeyboardRows[0]; // 0xFE: CAPS, Z, X, C, V
+            if ((highByte & 0x02) == 0) result &= KeyboardRows[1]; // 0xFD: A, S, D, F, G
+            if ((highByte & 0x04) == 0) result &= KeyboardRows[2]; // 0xFB: Q, W, E, R, T
+            if ((highByte & 0x08) == 0) result &= KeyboardRows[3]; // 0xF7: 1, 2, 3, 4, 5
+            if ((highByte & 0x10) == 0) result &= KeyboardRows[4]; // 0xEF: 0, 9, 8, 7, 6
+            if ((highByte & 0x20) == 0) result &= KeyboardRows[5]; // 0xDF: P, O, I, U, Y
+            if ((highByte & 0x40) == 0) result &= KeyboardRows[6]; // 0xBF: ENTER, L, K, J, H
+            if ((highByte & 0x80) == 0) result &= KeyboardRows[7]; // 0x7F: SPACE, SYM, M, N, B
+
+            // The top 3 bits (5, 6, 7) are unused by the keyboard and usually return 1 on a real Spectrum
+            return (byte)(result | 0xE0);
+        }
+
+        // Return 0xFF for unhandled ports
+        return 0xFF; 
+    }
+
+    public void WritePort(ushort portAddress, byte portValue)
+        {
+
+        }
+}
+}

Core/Io/SimpleIoBus.cs

@@ -1,20 +0,0 @@
-using System.Diagnostics;
-using Core.Interfaces;
-
-namespace Core.Io
-{
-    public class SimpleIoBus : IIoBus
-    {
-        public byte Read(ushort port)
-        {
-            // If the CPU reads an unconnected port, the Z80 usually sees 0xFF
-            return 0xFF;
-        }
-
-        public void Write(ushort port, byte value)
-        {
-            // For now, let's just log it to the Visual Studio Output window
-            Debug.WriteLine($"Hardware I/O Write -> Port: 0x{port:X4}, Value: 0x{value:X2}");
-        }
-    }
-}