diff --git a/lib/xdrmappings/GwXDRMappings.cpp b/lib/xdrmappings/GwXDRMappings.cpp
index 0af8f62..725ca53 100644
--- a/lib/xdrmappings/GwXDRMappings.cpp
+++ b/lib/xdrmappings/GwXDRMappings.cpp
@@ -230,36 +230,112 @@ void GwXDRMappings::begin()
                     LOG_DEBUG(GwLog::DEBUG, "no type definition for %s", def->toString().c_str());
                     continue;
                 }
-                long n2kkey=def->n2kKey();
-                auto it=n2kMap.find(n2kkey);
-                if (it == n2kMap.end()){
-                    LOG_DEBUG(GwLog::DEBUG,"insert mapping with key %ld",n2kkey);
-                    GwXDRMapping *mapping = new GwXDRMapping(def, type);
-                    n2kMap[n2kkey]=mapping;
+                long n2kkey = def->n2kKey();
+                auto it = n2kMap.find(n2kkey);
+                GwXDRMapping *mapping = new GwXDRMapping(def, type);
+                if (it == n2kMap.end())
+                {
+                    LOG_DEBUG(GwLog::DEBUG, "insert mapping with key %ld", n2kkey);
+                    GwXDRMapping::MappingList mappings;
+                    mappings.push_back(mapping);
+                    n2kMap[n2kkey] = mappings;
                 }
-                else{
-                    LOG_DEBUG(GwLog::DEBUG,"append mapping with key %ld",n2kkey);
-                    it->second->addMappingDef(def);
+                else
+                {
+                    LOG_DEBUG(GwLog::DEBUG, "append mapping with key %ld", n2kkey);
+                    it->second.push_back(mapping);
                 }
                 //for nmea0183 there could be multiple entries
                 //as potentially there are different units that we can handle
                 //so after we inserted the definition we do additional type lookups
-                while (type != NULL){
-                    String n183key=GwXDRMappingDef::n183key(def->xdrName,
-                        type->xdrtype,type->xdrunit);
-                    auto it=n183Map.find(n183key);
-                    if (it == n183Map.end()){
-                        LOG_DEBUG(GwLog::DEBUG,"insert mapping with n183key %s",n183key.c_str());
-                        n183Map[n183key]=new GwXDRMapping(def,type);
+                while (type != NULL)
+                {
+                    String n183key = GwXDRMappingDef::n183key(def->xdrName,
+                                                              type->xdrtype, type->xdrunit);
+                    auto it = n183Map.find(n183key);
+                    if (it == n183Map.end())
+                    {
+                        LOG_DEBUG(GwLog::DEBUG, "insert mapping with n183key %s", n183key.c_str());
+                        GwXDRMapping::MappingList mappings;
+                        mappings.push_back(mapping);
+                        n183Map[n183key] = mappings;
                     }
-                    else{
-                        LOG_DEBUG(GwLog::DEBUG,"append mapping with n183key %s",n183key.c_str());
-                        it->second->addMappingDef(def);
+                    else
+                    {
+                        LOG_DEBUG(GwLog::DEBUG, "append mapping with n183key %s", n183key.c_str());
+                        it->second.push_back(mapping);
                     }
-                    type=findType(code,&typeIndex);
-                    if (! type) break;
+                    type = findType(code, &typeIndex);
+                    if (!type)
+                        break;
+                    mapping=new GwXDRMapping(def,type);    
                 }
             }
         }
     }
+}
+
+/**
+ * select the best matching mapping
+ * depending on the instance id
+ */
+GwXDRFoundMapping GwXDRMappings::selectMapping(GwXDRMapping::MappingList *list,int instance){
+    GwXDRMapping *candidate=NULL;
+    for (auto mit=list->begin();mit != list->end();mit++){
+        GwXDRMappingDef *def=(*mit)->definition;
+        //if there is no instance we take a mapping with instance type ignore
+        //otherwise we prefer a matching instance before we use auto/ignore
+        if (instance < 0){
+            if (def->instanceMode != GwXDRMappingDef::IS_IGNORE) continue;
+            LOG_DEBUG(GwLog::DEBUG,"found mapping %s",def->toString().c_str());
+            return GwXDRFoundMapping(*mit);
+        }
+        else{
+            switch(def->instanceMode){
+                case GwXDRMappingDef::IS_SINGLE:
+                    if (def->instanceId == instance){
+                        LOG_DEBUG(GwLog::DEBUG,"found mapping %s",def->toString().c_str());
+                        return GwXDRFoundMapping(*mit,instance); 
+                    }
+                case GwXDRMappingDef::IS_AUTO:
+                    candidate=*mit;
+                    break;
+                default:
+                    break;    
+            }
+        }
+    }
+    if (candidate != NULL){
+        LOG_DEBUG(GwLog::DEBUG,"found mapping %s",candidate->definition->toString().c_str());
+        return GwXDRFoundMapping(candidate,instance);
+    }
+    return GwXDRFoundMapping();
+}
+GwXDRFoundMapping GwXDRMappings::getMapping(String xName,String xType,String xUnit){
+    //get an instance suffix from the name and separate it
+    int sepIdx=xName.indexOf('#');
+    int instance=-1;
+    if (sepIdx>=0){
+        String istr=xName.substring(sepIdx+1);
+        xName=xName.substring(0,sepIdx);
+        instance=istr.toInt();
+    }
+    if (xName == "") return GwXDRFoundMapping();
+    String n183Key=GwXDRMappingDef::n183key(xName,xType,xUnit);
+    auto it=n183Map.find(n183Key);
+    if (it == n183Map.end()) {
+        LOG_DEBUG(GwLog::DEBUG,"find n183mapping for %s,i=%d - nothing found",n183Key.c_str(),instance);
+        return GwXDRFoundMapping();
+    }
+    return selectMapping(&(it->second),instance);
+}
+GwXDRFoundMapping GwXDRMappings::getMapping(GwXDRCategory category,int selector,int field,int instance){
+    long n2kKey=GwXDRMappingDef::n2kKey(category,selector,field);
+    auto it=n2kMap.find(n2kKey);
+    if (it == n2kMap.end()){
+        LOG_DEBUG(GwLog::DEBUG,"find n2kmapping for c=%d,s=%d,f=%d,i=%d - nothing found",
+            (int)category,selector,field,instance);
+        return GwXDRFoundMapping();
+    }
+    return selectMapping(&(it->second),instance);
 }
\ No newline at end of file
diff --git a/lib/xdrmappings/GwXDRMappings.h b/lib/xdrmappings/GwXDRMappings.h
index 85bf00c..a53eea8 100644
--- a/lib/xdrmappings/GwXDRMappings.h
+++ b/lib/xdrmappings/GwXDRMappings.h
@@ -123,23 +123,39 @@ class GwXDRMappingDef{
         rt += xdrUnit;
         return rt;
     }
-    typedef std::vector<GwXDRMappingDef*> MappingList;
     private:
     static bool handleToken(String tok,int index,GwXDRMappingDef *def);
 };
 class GwXDRMapping{
     public:
-        GwXDRMappingDef::MappingList definitions;
+        GwXDRMappingDef *definition;
         GwXDRType *type;
         GwXDRMapping(GwXDRMappingDef *definition,GwXDRType *type){
-            this->definitions.push_back(definition);
+            this->definition=definition;
             this->type=type;
         }
-        void addMappingDef(GwXDRMappingDef *definition){
-            this->definitions.push_back(definition);
+        typedef std::vector<GwXDRMapping*> MappingList;
+        typedef std::map<String,MappingList> N138Map;
+        typedef std::map<long,MappingList> N2KMap;
+};
+class GwXDRFoundMapping{
+    public:
+        GwXDRMappingDef *definition=NULL;
+        GwXDRType *type=NULL;
+        int instanceId=-1;
+        bool empty=true;
+        GwXDRFoundMapping(GwXDRMappingDef *definition,GwXDRType *type){
+            this->definition=definition;
+            this->type=type;
+            empty=false;
         }
-        typedef std::map<String,GwXDRMapping*> N138Map;
-        typedef std::map<long,GwXDRMapping*> N2KMap;
+        GwXDRFoundMapping(GwXDRMapping* mapping,int instance=-1){
+            this->definition=mapping->definition;
+            this->type=mapping->type;
+            this->instanceId=instance;
+            empty=false;
+        }
+        GwXDRFoundMapping(){}
 };
 
 class GwXDRMappings{
@@ -148,13 +164,14 @@ class GwXDRMappings{
      GwConfigHandler *config;
      GwXDRMapping::N138Map n183Map;
      GwXDRMapping::N2KMap n2kMap;
+     GwXDRFoundMapping selectMapping(GwXDRMapping::MappingList *list,int instance);
     public:
         GwXDRMappings(GwLog *logger,GwConfigHandler *config);
         void begin();
         //get the mappings
         //the returned mapping will exactly contain one mapping def
-        GwXDRMapping getMapping(String xName,String xType,String xUnit);
-        GwXDRMapping getMapping(GwXDRCategory category,int selector,int field=0,int instance=0);
+        GwXDRFoundMapping getMapping(String xName,String xType,String xUnit);
+        GwXDRFoundMapping getMapping(GwXDRCategory category,int selector,int field=0,int instance=-1);
 
 };