Abstract: In this paper a methodology for architecture oriented Rapid Prototyping is presented. In the very early development phases concept-oriented Rapid Prototyping is used to clarify the requirements between the customer and the contractor. In the second, more complex phase of Rapid Prototyping, the architecture of the target system is used. So this kind of Rapid Prototyping is called "architecture-oriented Rapid Prototyping". Most Electronic Control Units (ECU) use microcontrollers with plenty of on-chip peripherals, sometimes application-specific microcontrollers with non-standard peripherals are used. But then, all these peripheral components must be present in the Rapid Prototyping system. To obtain this we developed an interface module with a FPGA for the peripheral parts of microcontroller based designs as well as a prototyping ECU which can be programmed with CASE-tools.