Domestic study of EnDat protocol limited to reading position from the encoder, the registers of encoders had never been used, while the registers contained important parameters. According to the handbook of EnDat protocol, this paper designed the interface circuit for accessing the registers of heidenhain LC183 absolute linear optical encoder; tested and analyzed the timing sequences between siemens SMC20 and heidenhain LC183 absolute linear optical encoder, programed a process on FPGA and realized the register access timing sequences. Experiments showed that the designed interface circuit and the realized timing sequences can be used to read the registers of heidenhain LC183 absolute linear optical encoder normally.