An arrangement for a system for controlling, monitoring, communication etc. comprises locally deployed module units which each perform one or more local function(s). The system also comprises one or more system-functioning-determining unit(s) at a higher level than said module units. Also included are one or more connection(s) connecting said units. Each module unit is connected to the connection concerned via a connection facility or connection point. The facility or point comprises one or more microprocessor(s) (microprocessor setup(s)) arranged with compatibility with signalling appearing on the connection according to the rules of systems engineering which apply, and with a higher-level function in relation to the module unit. The invention also relates to a method for said system and a contact arrangement for connection of a module unit to the connection. The invention makes possible outstanding separation of system functions and module unit functions, the result of which is that the various part functions can be produced individually with hardware and used by the system/module unit constructor.