First OpCode Decoding attempt

ParsonsMegadrive.Core/Memory/MdMemoryBus.cs

@@ -0,0 +1,49 @@
+using System;
+using ParsonsMegadrive.Core.Interfaces;
+
+namespace ParsonsMegaDrive.Core.Memory
+{
+    public class MdMemoryBus : IMemoryBus
+    {
+        // For testing, we'll just give it a flat 16MB array to represent the whole address space.
+        // Later, we will map this properly to ROM (0x000000), Work RAM (0xFF0000), etc.
+        private readonly byte[] _memory = new byte[16 * 1024 * 1024];
+
+        public byte Read8(uint address)
+        {
+            return _memory[address & 0xFFFFFF]; // 24-bit address mask
+        }
+
+        public void Write8(uint address, byte value)
+        {
+            _memory[address & 0xFFFFFF] = value;
+        }
+
+        public ushort Read16(uint address)
+        {
+            // BIG-ENDIAN: High byte comes first!
+            byte high = Read8(address);
+            byte low = Read8(address + 1);
+            return (ushort)((high << 8) | low);
+        }
+
+        public void Write16(uint address, ushort value)
+        {
+            Write8(address, (byte)(value >> 8));   // High byte
+            Write8(address + 1, (byte)(value & 0xFF)); // Low byte
+        }
+
+        public uint Read32(uint address)
+        {
+            ushort highWord = Read16(address);
+            ushort lowWord = Read16(address + 2);
+            return (uint)((highWord << 16) | lowWord);
+        }
+
+        public void Write32(uint address, uint value)
+        {
+            Write16(address, (ushort)(value >> 16));
+            Write16(address + 2, (ushort)(value & 0xFFFF));
+        }
+    }
+}