Design of Modem Chip Based On HART Communication Protocol Yu Xiao-yi1, 2 Yang Zhi-jia1 ( 1. Shenyang Institute of Automation of the Chinese Academy of Sciences, Shenyang, 110016) (2. Graduate School of the Chinese Academy of Sciences, Beijing, 100039) Abstract: This paper presents a design scheme of digital modem based on HART communictaion protocol. For the modulation part of the design, traditional DDS technology is improved to implement CPFSK modulation. As a result, the performance of spur and error of digital part are optimized. In the demoduation part, CPFSK demodulation is implemented and digital filters are adopted to get good precision and strong ability of anti-jamming. According to performance analysis and simulation results, the advantages of the design scheme above are proved. Key words: HART ; CPFSK; DDS ;Modulate;Demodulate