What is the difference between HART protocol and RS485 protocol? What are the differences between the HART protocol and RS485 protocol? The differences between the HART protocol and RS485 protocol are as follows: 1. Different concepts. The HART protocol uses the FSK frequency shift keying signal based on the Bell202 standard, and superimposes an audio digital signal with an amplitude of 0.5mA on the low frequency 4-20mA analog signal for two-way digital communication; For RS-485 protocol, the typical serial communication standards are RS232 and RS485, which define voltage, impedance, etc., but do not define software protocol. 2. Different communication modes HART communication adopts the half duplex communication mode, which is characterized by the realization of digital signal communication on the existing analog signal transmission line. It is a transitional product in the transition from analog system to digital system, so it has strong market competitiveness in the current transition period and has been developed rapidly; Electrical characteristics of RS-485: logic "1" is represented by+(2-6) V voltage difference between two lines; The logic "0" is represented by the voltage difference between two lines as - (2-6) V. If the interface signal level is lower than RS-232-C, it is not easy to damage the chip of the interface circuit, and this level is compatible with the TTL level, which can facilitate the connection with the TTL circuit. 3. Specification The HART communication of different specifications is based on the Bell 202 standard and uses frequency shift keying (FSK) to communicate at a rate of 1200bps. The signal frequencies representing 0 and 1 bit values are 2200 and 1200Hz respectively. The low-level signal is superimposed on the analog measurement signal of 4 to 20mA, and will not cause any interference to the analog signal; And The maximum transmission distance standard value of RS-485 interface is 4000 feet, which can actually reach 3000 meters. In addition, RS-232-C interface only allows to connect one transceiver on the bus, that is, single station capability. The RS-485 interface allows up to 128 transceivers to be connected on the bus. That is, it has the ability of multi stations, so that users can use a single RS-485 interface to easily establish a device network. Do you understand this explanation?
