This paper proposes a new CLB architecture for FPGAs and an associated testing technique that detects routing errors caused by SEUs in the SRAM configuration memory of the FPGA. The proposed testing technique detects all possible routing errors including bridging faults, and requires a single configuration of only the LUTs of the FPGA. Any routing error that affects the logic of the circuit is detected by the proposed technique in a maximum of 8 clock cycles. It is noteworthy that the time required for error detection is independent of both the number of switch matrices and the number of logic blocks in the FPGA. © 2005 IEEE.