Abstract: This paper introduces the basic principles of photoelectric current transformers and their high-voltage side digital output encoding modules, focusing on the design process of the CRC encoding module. The CRC checksum is theoretically analyzed, and a VHDL program for implementing the CRC checksum is given and implemented on a Field Programmable Gate Array (FPGA). The framed data is then encoded using Manchester code and transmitted to the low-voltage side via optical fiber. This scheme can meet the speed and reliability requirements of photoelectric current transformers for data communication and has broad application prospects in power communication systems. Keywords: Photoelectric current transformer; CRC; Field Programmable Gate Array; Manchester encoding 1 Introduction Current transformers are widely used current sensing and transmission devices in power systems, mainly for relay protection and electrical measurement. Their accuracy and reliability have a significant impact on the safe and stable operation of power systems. However, with the increasing capacity and voltage levels of power systems, traditional electromagnetic current transformers (CTs) have encountered insurmountable challenges. The next-generation electronic current transformer based on optical and electronic technologies—the photoelectric current transformer—overcomes a series of problems existing in traditional current transformers, such as magnetic saturation and ferroresonance, while retaining its mature sensing principle technology. Combined with novel optoelectronic technology, it possesses advantages such as high precision and intelligence that traditional electromagnetic transformers cannot match, making its application prospects very optimistic. The high-voltage side digital output encoding module designed in this paper is an important component of the photoelectric current transformer. Its implementation enables faster and more accurate digital communication between the high-voltage and low-voltage sides. For details, please click: Design of High-Voltage Side Encoding Module for Photoelectric Current Transformer