Identifier, read/write, for assigning an address to the Pluto it is connected to. Each Pluto connected to the Pluto safety bus needs an IDFIX. The IDFIX number is programmable, i.e. the user can choose the number. IDFIX is an identifier circuit which gives each Pluto an address on the bus. It contains an identification code which can be read by the system. The identification code is declared in the PLC program so that the correct part of the PLC program is executed by each specific Pluto. The use of IDFIX is mandatory in a multi-Pluto project, but voluntary if a unit works alone. If one Pluto in a multi-Pluto project needs to be replaced it is possible to let the new Pluto selfload the PLC program from another Pluto on the bus. The IDFIX will ensure that the new Pluto has the correct address on the bus.