A method of generating at least one instruction set from a plurality of program instructions, said plurality of program instructions comprising a plurality of instruction fields each of said instruction fields operable on decoding to generate control signals for transmission by individual command buses, said method comprising the steps of: determining which combination of command buses each instruction is operable to communicate control signals to and forming a cluster of instructions from instructions that communicate control signals to a same combination of command buses; developing at least one instruction set for at least some of said instruction clusters, said at least one instruction set having fewer bits than said program instruction; specifying a number of identification bits within said at least one instruction set operable to identify said instruction set; determining a number of bits required for each instruction field within said at least one instruction set to specify all possible control signals that can be sent by said at least one instruction set along a respective one of said command buses and reallocating any bits that are allocated to said instruction field that are in excess of said determined required number to said identification bits, such that an increased number of different instruction sets can be identified by said identification bits.