use strict;
use warnings;
use v5.10;
use Win32::API;

my $ObjDll = {
  _OpenPort         => GetRefToDllFunction("$Path2Dll", 'AdsPortOpen',        '', 'N'),
  _LocalAddr        => GetRefToDllFunction("$Path2Dll", 'AdsGetLocalAddress', '???', 'N')
};

sub GetRefToDllFunction(....);


# Port öffnen, Rückgabewert des offenen Ports
my $Port = $ObjDll->{_OpenPort}->Call();   

# Lesen der NetId
my $Result = $ObjDll->{_LocalAddr}->Call(???);