An instruction word is used to transfer information about whether the instruction word pertains to mode setting of a functional block. Instruction words included in the program code are processed in at least a first decoding step and a second decoding step, wherein in the first decoding step, said information included in the instruction word is examined. On the basis of the examination, it is determined whether the mode of one or more functional blocks is to be set or whether the second decoding step is to be taken, in which the instruction word is decoded to be run by one or more of said functional blocks. The invention also relates to a processor and an electronic device, in which the method can be implemented. The invention further relates to a program, in which a program code is provided for implementing the method.