diff --git a/Modbus.Net/src/Base.Common/BaseProtocal.cs b/Modbus.Net/src/Base.Common/BaseProtocal.cs
index 3873ac5..c31b6ce 100644
--- a/Modbus.Net/src/Base.Common/BaseProtocal.cs
+++ b/Modbus.Net/src/Base.Common/BaseProtocal.cs
@@ -85,13 +85,16 @@ namespace Modbus.Net
                 {
                     if (Protocals.ContainsKey(protocalName))
                         protocalUnitReturn = Protocals[protocalName];
-                    //自动寻找存在的协议并将其加载
-                    var protocalUnit =
-                        Activator.CreateInstance(type.GetTypeInfo().Assembly.GetType(protocalName)) as TProtocalUnit;
-                    if (protocalUnit == null)
-                        throw new InvalidCastException($"No ProtocalUnit {nameof(TProtocalUnit)} implemented");
-                    protocalUnit.Endian = Endian;
-                    Register(protocalUnit);
+                    else
+                    {
+                        //自动寻找存在的协议并将其加载
+                        var protocalUnit =
+                            Activator.CreateInstance(type.GetTypeInfo().Assembly.GetType(protocalName)) as TProtocalUnit;
+                        if (protocalUnit == null)
+                            throw new InvalidCastException($"No ProtocalUnit {nameof(TProtocalUnit)} implemented");
+                        protocalUnit.Endian = Endian;
+                        Register(protocalUnit);
+                    }                    
                 }
                 return protocalUnitReturn ?? Protocals[protocalName];
             }