Foundation Fieldbus has two communication rates: low-speed H 1 and high-speed H2. The transmission rate of H 1 is 3 1.25kbps, and the communication distance can reach 1900m (which can be extended by repeater), which can support the explosion-proof environment powered by bus. The transmission of H2 can be 1Mbps and 2.5Mbps, and the communication distance is 750m and 500m respectively. The physical transmission medium can support twisted pair, optical cable and wireless transmission, and the protocol conforms to IEC 1 158-2 standard. The transmission signal of its physical medium adopts Manchester coding.