The L-N bus could be widely used in building electrical intelligent monitoring system as the characteristics of strong anti-interference, low application cost and autonomy. Aiming at the CPU overhead problem caused by the current software implementation of L-N bus communication protocol, a configurable L-N bus controller is designed to achieve the hardening of communication protocol. Through the in-depth analysis of L-N bus communication protocol, the feasibility of the protocol hardening is confirmed. On this basis, we established the hardware architecture, each component module and its relationship of the protocol controller. Then, we described function of each module in the behavior layer, simulated its logic function and implemented the prototype verification on the FPGA. Finally, we simulate the application scenario of the controller by the construction of the physical layer test platform and test its functions, including communication test, configurable function test and reliability test. The results show that the L-N bus controller could well implement the protocol specification, and shows good reliability. It can improve the CPU efficiency by 46% in the test environment.