ZX Spectrum draft DB access

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum48K/ZX48.cs

@@ -93,6 +93,16 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
             return bank[index];
         }
 
+		/// <summary>
+		///  Pushes a value onto the data bus that should be valid as long as the interrupt is true
+		/// </summary>
+		/// <param name="addr"></param>
+		/// <returns></returns>
+		public override byte PushBus()
+		{
+			return 0xFF;
+		}
+
 		/// <summary>
 		/// Simulates writing to the bus (no contention)
 		/// Paging should be handled here