Abstract: An emulator block (30) for use in the development or testing of an embedded system, the emulator block (30) being configured to model a processing block (20) that includes a bus interface (22) and processing core logic (28), said emulator block comprising: an emulator bus interface comprising bus specific logic (24) and a Register Block (26), said emulator bus interface being configured to be substantially identical to the bus interface of the processing block that the emulator block is to model; and a core block emulator (32) configured, in use, to supply and receive signals to and from the Register Block (26) which mimic signals supplied and received to and from the processing core logic (28) of the processing block that the emulator block is to model.