diff --git a/SabreTools.Library/DatFiles/Listxml.cs b/SabreTools.Library/DatFiles/Listxml.cs
index 40bdddc3..0c160083 100644
--- a/SabreTools.Library/DatFiles/Listxml.cs
+++ b/SabreTools.Library/DatFiles/Listxml.cs
@@ -207,19 +207,27 @@ namespace SabreTools.Library.DatFiles
                         break;
 
                     case "chip":
-                        datItems.Add(new Chip
+                        var chip = new Chip
                         {
                             Name = reader.GetAttribute("name"),
                             Tag = reader.GetAttribute("tag"),
                             ChipType = reader.GetAttribute("type").AsChipType(),
-                            Clock = reader.GetAttribute("clock"),
 
                             Source = new Source
                             {
                                 Index = indexId,
                                 Name = filename,
                             },
-                        });
+                        };
+
+                        // Set the clock
+                        if (reader.GetAttribute("clock") != null)
+                        {
+                            if (Int64.TryParse(reader.GetAttribute("clock"), out long clock))
+                                chip.Clock = clock;
+                        }
+
+                        datItems.Add(chip);
 
                         reader.Read();
                         break;
@@ -1430,7 +1438,7 @@ namespace SabreTools.Library.DatFiles
                         xtw.WriteRequiredAttributeString("name", chip.Name);
                         xtw.WriteOptionalAttributeString("tag", chip.Tag);
                         xtw.WriteOptionalAttributeString("type", chip.ChipType.FromChipType());
-                        xtw.WriteOptionalAttributeString("clock", chip.Clock);
+                        xtw.WriteOptionalAttributeString("clock", chip.Clock?.ToString());
                         xtw.WriteEndElement();
                         break;
 
diff --git a/SabreTools.Library/DatFiles/SabreDat.cs b/SabreTools.Library/DatFiles/SabreDat.cs
index a4c45155..4ec1c350 100644
--- a/SabreTools.Library/DatFiles/SabreDat.cs
+++ b/SabreTools.Library/DatFiles/SabreDat.cs
@@ -400,7 +400,6 @@ namespace SabreTools.Library.DatFiles
                                     Name = reader.GetAttribute("name"),
                                     Tag = reader.GetAttribute("tag"),
                                     ChipType = reader.GetAttribute("chiptype").AsChipType(),
-                                    Clock = reader.GetAttribute("clock"),
 
                                     Source = new Source
                                     {
@@ -408,6 +407,14 @@ namespace SabreTools.Library.DatFiles
                                         Name = filename,
                                     },
                                 };
+
+                                // Set the clock
+                                if (reader.GetAttribute("clock") != null)
+                                {
+                                    if (Int64.TryParse(reader.GetAttribute("clock"), out long clock))
+                                        (datItem as Chip).Clock = clock;
+                                }
+
                                 break;
 
                             case "configuration":
@@ -1254,7 +1261,7 @@ namespace SabreTools.Library.DatFiles
                         xtw.WriteRequiredAttributeString("name", chip.Name);
                         xtw.WriteOptionalAttributeString("tag", chip.Tag);
                         xtw.WriteOptionalAttributeString("chiptype", chip.ChipType.FromChipType());
-                        xtw.WriteOptionalAttributeString("clock", chip.Clock);
+                        xtw.WriteOptionalAttributeString("clock", chip.Clock.ToString());
                         xtw.WriteEndElement();
                         break;
 
diff --git a/SabreTools.Library/DatItems/Chip.cs b/SabreTools.Library/DatItems/Chip.cs
index 0fe419c9..5e63f97b 100644
--- a/SabreTools.Library/DatItems/Chip.cs
+++ b/SabreTools.Library/DatItems/Chip.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 
@@ -40,7 +41,7 @@ namespace SabreTools.Library.DatItems
         /// Clock speed
         /// </summary>
         [JsonProperty("clock", DefaultValueHandling = DefaultValueHandling.Ignore)]
-        public string Clock { get; set; }
+        public long? Clock { get; set; }
 
         #endregion
 
@@ -75,7 +76,10 @@ namespace SabreTools.Library.DatItems
                 ChipType = mappings[Field.DatItem_ChipType].AsChipType();
 
             if (mappings.Keys.Contains(Field.DatItem_Clock))
-                Clock = mappings[Field.DatItem_Clock];
+            {
+                if (Int64.TryParse(mappings[Field.DatItem_Clock], out long clock))
+                    Clock = clock;
+            }
         }
 
         #endregion
@@ -194,9 +198,9 @@ namespace SabreTools.Library.DatItems
                 return false;
 
             // DatItem_Clock
-            if (filter.DatItem_Clock.MatchesPositiveSet(Clock) == false)
+            if (filter.DatItem_Clock.MatchesPositive(null, Clock) == false)
                 return false;
-            if (filter.DatItem_Clock.MatchesNegativeSet(Clock) == true)
+            if (filter.DatItem_Clock.MatchesNegative(null, Clock) == true)
                 return false;
 
             return true;
diff --git a/SabreTools.Library/Filtering/Filter.cs b/SabreTools.Library/Filtering/Filter.cs
index 08093981..1b15156f 100644
--- a/SabreTools.Library/Filtering/Filter.cs
+++ b/SabreTools.Library/Filtering/Filter.cs
@@ -165,7 +165,7 @@ namespace SabreTools.Library.Filtering
         // Chip
         public FilterItem<string> DatItem_Tag { get; private set; } = new FilterItem<string>();
         public FilterItem<ChipType> DatItem_ChipType { get; private set; } = new FilterItem<ChipType>() { Positive = ChipType.NULL, Negative = ChipType.NULL };
-        public FilterItem<string> DatItem_Clock { get; private set; } = new FilterItem<string>();
+        public FilterItem<long?> DatItem_Clock { get; private set; } = new FilterItem<long?>() { Positive = null, Negative = null, Neutral = null };
 
         // Condition
         public FilterItem<string> DatItem_Mask { get; private set; } = new FilterItem<string>();
@@ -730,7 +730,7 @@ namespace SabreTools.Library.Filtering
                     break;
 
                 case Field.DatItem_Clock:
-                    SetStringFilter(DatItem_Clock, value, negate);
+                    SetOptionalLongFilter(DatItem_Clock, value, negate);
                     break;
 
                 // Condition