Abstract: A configurable electronic device which is compatible with a configuration bitstream of a prior generation configurable electronic device. The configurable device has a first configurable domain which is configurable with the configuration bitstream of the prior generation device and a second configurable domain which is optionally configurable. To function as the prior generation configurable device, the configurable device is loaded with the bitstream of the prior generation configurable device. To utilize the second configurable domain, another bitstream is concatenated to the bitstream intended for the first configurable domain. In a first embodiment, a signal is utilized to indicate when the first configurable domain is full of configuration bits, thereby indicating that the second configurable domain may load forthcoming bits. In a second embodiment, the configuration bitstream for the first configurable domain includes a bit to indicate whether a successive configurable domain may load forthcoming bits.