An important link in the flexible DC transmission control and protection system is the communication between the internal control and external equipment, which requires high speed and stability. The localization substitution of the control and protection system puts forward higher requirements for the stability and compatibility of its communication. The measurement required by the inner loop control is collected, processed and transmitted by the merging unit or transformer. Its communication signal has the characteristics of positive and negative Manchester code and various baud rate coding. The conventional decoding algorithm is easy to fail due to poor compatibility. On the basis of the standard of electronic current and voltage transformer, this paper studies and analyzes the encoding and decoding process of its data frame format of the communication protocol, and puts forward and implements the design method for IEC60044-8 communication interface based on positive and negative Manchester code and baud rate dynamic adaptation of domestic FPGA chip. The experimental results show that the scheme has strong real-time performance, high recognition accuracy and strong compatibility, and has a wide range of application value.