I have a bunch of S2’s loaded with API2/router firmware which I want to use as end nodes. How do I address them? It seems as if I have to use their hardware address (serial number/mac address) as I cant configure them with any other address with XCTU. Is this right?
That is correct. The modules 64 bit serial number is the Source address. You set the DL and DH or in this case the Destination Address field of the API frame with the MAC address of the node you want to send the data to.