When using the RS485 interface, for a specific transmission line, the maximum cable length allowed for data signal transmission from the RS485 interface to the load is inversely proportional to the baud rate of the signal transmission. That is to say, the maximum transmission distance of RS485 can reach 9.6 kilometers in theory. The condition is that the communication wire is high-quality and meets the standard, the baud rate is 9600, and only one 485 device is loaded, so that the communication distance can reach 1200 meters, so the actual and stable communication distance of the 485 bus is usually less than 1200 meters. It should be judged according to the model of the chip in the 485 converter and the model of the 485 device chip, and the load capacity can only be determined according to the chip with a lower index. The length of the branch line from the bus to each terminal device should be as short as possible, generally not exceeding 5 meters.



































In theory, the longest transmission distance of RS485 can reach 1200 meters, but the transmission distance in practical applications is shorter than 1200 meters. According to the 485 bus structure theory, under the premise of an ideal environment, the 485 bus transmission distance can reach 1200 meters. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. At least 0.4mm square or use a standard network cable. In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. Serial data communications standards - RS-232, RS-422, what is rs485 cable & RS-485 were widely used for data transfer providing easy connectivity for the time and they can still be found today. How many devices can be connected to a bus? Grounds between buildings may vary by a small voltage, but with very low impedance and hence the possibility of catastrophic currents - enough to melt signal cables, PCB traces, and transceiver devices. Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance.



































Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. The value of each termination resistor should be equal to the cable characteristic impedance (typically, 120 ohms for twisted pairs). The two values provide a sufficient margin for a reliable data transmission even under severe signal degradation across the cable and connectors. PC environment. 8P8C modular connectors are used in this case. The specific transmission distance depends on the surrounding environment. RS485 has no specific physical shape. Clueing in from its name, this is a USB to RS485 converter with industrial-grade features. The longer the communication distance, the higher the baud rate, the thinner the wire diameter, the worse the wire quality, the worse the quality of the converter, and the insufficient power supply of the converter (passive Converter), the stronger the lightning protection, these will reduce the real load quantity. If there are many load 485 devices, the wire impedance is not up to the standard, the wire diameter is too thin, the converter quality is poor, the equipment lightning protection is complicated, and the baud rate is increased. Generally, there are three levels of 485 chip load capacity-32 units, 128 units and 256 units.



































Some people say that the 485 bus can carry 128 devices for communication. In fact, not all 485 converters can be equipped with 128 devices. If long-distance transmission is really needed, optical fiber can be used as the propagation medium, and a photoelectric converter is added at both ends of the transceiver. The diagram below shows potentials of the A (blue) and B (red) pins of an RS-485 line during transmission of one byte (0xD3, least significant bit first) of data using an asynchronous start-stop method. This includes speed control using Variable Frequency Drives (VFD) or inverters, as well as controlling simple PLC and HMI network systems. RS485 RS-485 is a standard that allows high speed data transmission along with multiple transmitters and receivers and this makes it able to be incorporated as a network solution. As a rule of thumb, the speed in bit/s multiplied by the length in metres should not exceed 108. Thus a 50-meter cable should not signal faster than 2 Mbit/s. 2. It is not allowed to use a network cable with a wire diameter that is too thin, which will reduce the transmission distance and reduce the equipment that can be connected. The communication line should be as far away as possible from interference sources such as high-voltage wires, fluorescent lamps, etc. When the communication line cannot be avoided from interference sources such as power lines, the communication line should be perpendicular to the power line, not parallel, and cannot be bundled together, and use high-quality twisted-pair cables.