diff --git a/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ULA.cs b/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ULA.cs
index 398c0c958f..0124f6721e 100644
--- a/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ULA.cs
+++ b/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ULA.cs
@@ -98,6 +98,16 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         /// </summary>
         public int PortContentionOffset;
 
+        /// <summary>
+        /// Arbitrary offset for render table generation
+        /// </summary>
+        public int RenderTableOffset;
+
+        /// <summary>
+        /// The offset when return floating bus bytes
+        /// </summary>
+        public int FloatingBusOffset;
+
         /// <summary>
         /// The time in T-States for one scanline to complete
         /// </summary>
@@ -317,17 +327,9 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
             /// <param name="machineType"></param>
             private void InitRenderer(MachineType machineType)
             {
-                switch (machineType)
-                {
-                    case MachineType.ZXSpectrum16:
-                    case MachineType.ZXSpectrum48:
-                        Offset = 0;
-                        break;
-                }
-
                 for (var t = 0; t < _ula.FrameCycleLength; t++)
                 {
-                    var tStateScreen = t + 1 + _ula.InterruptStartTime;
+                    var tStateScreen = t + _ula.RenderTableOffset + _ula.InterruptStartTime;
 
                     if (tStateScreen < 0)
                         tStateScreen += _ula.FrameCycleLength;
@@ -458,7 +460,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
                 // calculate contention values
                 for (int t = 0; t < _ula.FrameCycleLength; t++)
                 {
-                    int shifted = (t + 1) + _ula.InterruptStartTime + Offset;
+                    int shifted = t + _ula.RenderTableOffset + _ula.InterruptStartTime;
                     if (shifted < 0)
                         shifted += _ula.FrameCycleLength;
                     shifted %= _ula.FrameCycleLength;
@@ -482,46 +484,6 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 
                     Renderer[t].ContentionValue = conPattern[pixByte];
                 }
-
-                // calculate floating bus values
-                for (int t = 0; t < _ula.FrameCycleLength; t++)
-                {
-                    int shifted = (t + 10) + _ula.InterruptStartTime;
-                    if (shifted < 0)
-                        shifted += _ula.FrameCycleLength;
-                    shifted %= _ula.FrameCycleLength;
-
-                    Renderer[t].FloatingBusAddress = 0;
-
-                    int line = shifted / _ula.ScanlineTime;
-                    int pix = shifted % _ula.ScanlineTime;
-                    if (line < _ula.FirstPaperLine || line >= (_ula.FirstPaperLine + 192))
-                    {
-                        Renderer[t].FloatingBusAddress = 0;
-                        continue;
-                    }
-                    int scrPix = pix - _ula.FirstPaperTState;
-                    if (scrPix < 0 || scrPix >= 128)
-                    {
-                        Renderer[t].FloatingBusAddress = 0;
-                        continue;
-                    }
-
-                    int pixByte = scrPix % 8;
-                    int chunk = scrPix % 16;
-
-                    switch (chunk)
-                    {
-                        case 0:
-                        case 2:
-                            Renderer[t].FloatingBusAddress = CalculateByteAddress(scrPix, line);
-                            break;
-                        case 1:
-                        case 3:
-                            Renderer[t].FloatingBusAddress = CalculateAttributeAddress(scrPix, line);
-                            break;
-                    }
-                }
             }
 
             private ushort CalculateByteAddress(int x, int y)
@@ -719,8 +681,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         /// <returns></returns>
         public void ReadFloatingBus(int tstate, ref int result)
         {
-            int off = 0;
-            tstate += off;
+            tstate += FloatingBusOffset;
             if (tstate >= RenderingTable.Renderer.Length)
                 tstate -= RenderingTable.Renderer.Length;
             if (tstate < 0)
diff --git a/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128K/ZX128.Screen.cs b/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128K/ZX128.Screen.cs
index 3e1aed6e24..92472c0e3b 100644
--- a/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128K/ZX128.Screen.cs
+++ b/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128K/ZX128.Screen.cs
@@ -22,6 +22,8 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 
             MemoryContentionOffset = 5;
             PortContentionOffset = 5;
+            RenderTableOffset = 1;
+            FloatingBusOffset = 1;
 
             BorderLeftTime = 24;
             BorderRightTime = 24;
diff --git a/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus2a/ZX128Plus2a.Screen.cs b/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus2a/ZX128Plus2a.Screen.cs
index 90f505d1f2..2cd69dcaa7 100644
--- a/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus2a/ZX128Plus2a.Screen.cs
+++ b/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus2a/ZX128Plus2a.Screen.cs
@@ -22,6 +22,8 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 
             MemoryContentionOffset = 7;
             PortContentionOffset = 7;
+            RenderTableOffset = 1;
+            FloatingBusOffset = 1;
 
             BorderLeftTime = 24;
             BorderRightTime = 24;
diff --git a/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum48K/ZX48.Screen.cs b/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum48K/ZX48.Screen.cs
index 5af98f944a..96624fe1d5 100644
--- a/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum48K/ZX48.Screen.cs
+++ b/BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum48K/ZX48.Screen.cs
@@ -16,12 +16,14 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 			// timing
 			ClockSpeed = 3500000;
             FrameCycleLength = 69888;
-            InterruptStartTime = 31;
+            InterruptStartTime = 30;
             InterruptLength = 32;
             ScanlineTime = 224;
 
-            MemoryContentionOffset = 5;
-            PortContentionOffset = 5;
+            MemoryContentionOffset = 6;
+            PortContentionOffset = 6;
+            RenderTableOffset = 2;
+            FloatingBusOffset = 1;
 
             BorderLeftTime = 24;
             BorderRightTime = 24;