Data processing apparatuses, methods of data processing, and non-transitory computer-readable media on which computer-readable code is stored defining logical configurations of processing devices are disclosed. In an apparatus, fetch circuitry retrieves a sequence of instructions and execution circuitry performs data processing operations with respect to data values in a set of registers. An auxiliary execution circuitry interface and a coprocessor interface to provide a connection to a coprocessor outside the apparatus are provided. Decoding circuitry generates control signals in dependence on the instructions of the sequence of instructions, wherein the decoding circuitry is responsive to instructions in a first subset of an instruction encoding space to generate the control signals to control the execution circuitry to perform the first data processing operations, and the decoding circuitry is responsive to instructions in a second subset of the instruction encoding space to generate the control signals in dependence on a configuration condition: to generate the control signals for the auxiliary execution circuitry interface when the configuration condition has a first state; and to generate the control signals for the coprocessor interface when the configuration condition has a second state.