Apparatus for connecting data processing equipment to a communications network includes hardware for a range of different communications standards. Also included is a coupler (preferably in the form of a cable) having a particular standard communications plug which contains an identifying code associated with that particular standard plug, which code is used to configure the apparatus to that particular standard. The apparatus contains a digital signal processor controlled by control code contained in a control store having associated therewith a standard identifier code. Control logic reads the standard identifier code associated with the control code and the standard identifying code in the coupler and enables the apparatus if the two match (or disables if they do not match). The control store can either contain only the code associated with a particular standard or it can contain all the code for a range of standards: in the latter case the control logic would allow the signal processor to access only the sections of the control store containing the relevant control code. The invention is particularly useful for connecting data processing equipment through a modem to different country telephone networks.