Move GetAdditionalErrorText to S7ErrorCodes

Sharp7.Rx/S7ErrorCodes.cs

@@ -1,4 +1,6 @@
-namespace Sharp7.Rx;
+#nullable enable
+
+namespace Sharp7.Rx;
 
 public static class S7ErrorCodes
 {
@@ -12,6 +14,18 @@ public static class S7ErrorCodes
         0x900000, // CPU: Address out of range
     };
 
+    private static readonly IReadOnlyDictionary<int, string> additionalErrorTexts = new Dictionary<int, string>
+    {
+        {0xC00000, "This happens when the DB does not exist."},
+        {0x900000, "This happens when the DB is not long enough."},
+        {
+            0x40000, """
+                     This error occurs when the DB is "optimized" or "PUT/GET communication" is not enabled.
+                     See https://snap7.sourceforge.net/snap7_client.html#target_compatibility.
+                     """
+        }
+    };
+
     /// <summary>
     ///     Some error codes indicate connection lost, in which case, the driver tries to reestablish connection.
     ///     Other error codes indicate a user error, like reading from an unavailable DB or exceeding
@@ -21,4 +35,7 @@ public static class S7ErrorCodes
     {
         return !notDisconnectedErrorCodes.Contains(errorCode);
     }
+
+    public static string? GetAdditionalErrorText(int errorCode) =>
+        additionalErrorTexts.TryGetValue(errorCode, out var text) ? text : null;
 }