- updated API documentation for command termination handler

src/iec61850/inc/iec61850_client.h

@@ -2255,7 +2255,12 @@ ControlObjectClient_setSynchroCheck(ControlObjectClient self, bool value);
  *
  * This callback is invoked whenever a CommandTermination+ or CommandTermination- message is received.
  * To distinguish between a CommandTermination+ and CommandTermination- please use the
- * ControlObjectClient_getLastApplError function.
+ * \ref ControlObjectClient_getLastApplError function.
+ *
+ * In case of CommandTermination+ the return value
+ * of \ref ControlObjectClient_getLastApplError has error=CONTROL_ERROR_NO_ERROR and
+ * addCause=ADD_CAUSE_UNKNOWN set. When addCause is different from ADD_CAUSE_UNKNOWN then the client
+ * received a CommandTermination- message.
  *
  * NOTE: Do not call \ref ControlObjectClient_destroy inside of this callback! Doing so will cause a dead-lock.
  *
@@ -2269,7 +2274,10 @@ typedef void (*CommandTerminationHandler) (void* parameter, ControlObjectClient
  *
  * This callback is invoked whenever a CommandTermination+ or CommandTermination- message is received.
  * To distinguish between a CommandTermination+ and CommandTermination- please use the
- * ControlObjectClient_getLastApplError function.
+ * \ref ControlObjectClient_getLastApplError function. In case of CommandTermination+ the return value
+ * of \ref ControlObjectClient_getLastApplError has error=CONTROL_ERROR_NO_ERROR and
+ * addCause=ADD_CAUSE_UNKNOWN set. When addCause is different from ADD_CAUSE_UNKNOWN then the client
+ * received a CommandTermination- message.
  *
  * \param self the ControlObjectClient instance
  * \param handler the callback function to be used