diff --git a/Modbus.Net/ModBus.Net/BaseProtocal.cs b/Modbus.Net/ModBus.Net/BaseProtocal.cs
index ab85f4c..52b092e 100644
--- a/Modbus.Net/ModBus.Net/BaseProtocal.cs
+++ b/Modbus.Net/ModBus.Net/BaseProtocal.cs
@@ -60,7 +60,7 @@ namespace ModBus.Net
         /// <returns></returns>
         public virtual byte[] SendReceive(params object[] content)
         {
-            return ProtocalLinker.SendReceive(ProtocalUnit.TranslateContent(content));
+            return AsyncHelper.RunSync(() => SendReceiveAsync(content));
         }
 
         /// <summary>
@@ -70,6 +70,10 @@ namespace ModBus.Net
         /// <returns></returns>
         public virtual async Task<byte[]> SendReceiveAsync(params object[] content)
         {
+            if (ProtocalLinker == null || !ProtocalLinker.IsConnected)
+            {
+                await ConnectAsync();
+            }
             return await ProtocalLinker.SendReceiveAsync(ProtocalUnit.TranslateContent(content));
         }
 
diff --git a/Modbus.Net/ModBus.Net/Siemens/SiemensTcpProtocal.cs b/Modbus.Net/ModBus.Net/Siemens/SiemensTcpProtocal.cs
index 05b8cc5..ec91abd 100644
--- a/Modbus.Net/ModBus.Net/Siemens/SiemensTcpProtocal.cs
+++ b/Modbus.Net/ModBus.Net/Siemens/SiemensTcpProtocal.cs
@@ -37,7 +37,7 @@ namespace ModBus.Net.Siemens
 
         public override async Task<byte[]> SendReceiveAsync(params object[] content)
         {
-            while (!ProtocalLinker.IsConnected)
+            if (ProtocalLinker == null || !ProtocalLinker.IsConnected)
             {
                 await ConnectAsync();
             }
@@ -51,7 +51,7 @@ namespace ModBus.Net.Siemens
 
         public override async Task<OutputStruct> SendReceiveAsync(ProtocalUnit unit, InputStruct content)
         {
-            if (!ProtocalLinker.IsConnected)
+            if (ProtocalLinker == null || !ProtocalLinker.IsConnected)
             {
                 if (connectTryCount > 10) return null;
                 return await await ConnectAsync().ContinueWith(answer => answer.Result ? base.SendReceiveAsync(unit, content) : null);