Method of altering the sequence of a data stored in a read only memory program

The invention relates to a method for changing the flow of a program stored in a read-only memory. To this end, the program has a plurality of program routines and to any program routine a sub-program is assigned which is stored in a first read-write memory. Storage locations of a second read-write memory are assigned to each program routine. A program routine calls the sub-program irrespective of the content of the assigned storage locations, provided a sub-program is allocated to said program routine.