A network node well suited for use in a distributed control network includes a housing containing the node electronics, and an external port for receiving a detachable plug-in module. The plug-in module contains a programmable memory which, when the plug-in module is attached, allows electronic interconnection between the electronics of the network node and the readable memory. The readable memory stores a unique node identifier which becomes associated with the node, and can also store functional program code for the particular node. Thus, a node can be easily and rapidly replaced or reprogrammed, without the need for specialized equipment to download the node identifier or functional program code, and without the possibility of erroneous manual entry of the node identifier. The plug-in module further includes a writable memory portion which can be used to store data during operation of the node, for later retrieval.