RS485 Serial Information > 자유게시판

In the picture above, noise is generated by magnetic fields from the environment. In the picture above, the general network topology of RS485 is shown. And that with an interface which does not require intelligent network hardware: the implementation on the software side is not much more difficult than with RS232. Depending of the information in the sent data, zero or more nodes on the line respond to the master. The maximum slew rate also limits the maximum communication speed on the line. We also see that there is a maximum slew rate defined for both RS232 and RS423. We also see that the maximum allowed voltage levels for all interfaces are in the same range, but that the signal level is lower for the faster interfaces. However this contradicts the facts that an idle mark state is a logical one and the termination polarization puts B at a higher voltage in Profibus guidelines. The termination also includes pull up and pull down resistors to establish bias for each data wire for the case when the lines are not being driven by any device.

When the connection is long, please use terminating resistors at both ends of the network, i.e., at the master and the farthest device. It should be noted that the connection wires between each device should be kept as short as possible to minimize signal attenuation and interference, improving communication reliability. This ensures that all security-related information and incidents are transmitted quickly and with high reliability. Because of this RS485 and the others can be used in situations with a severe ground level shift of several volts, where at the same time high bit rates are possible because the transition between logical 0 and logical 1 is only a few hundred millivolts. But some of the other interfaces are certainly interesting because they can be used in situations where RS232 is not appropriate. N nodes are connected in a multipoint RS485 network. Ring topology arranges network nodes in a circular configuration where each node connects to two others, forming a closed loop. That is why RS485 is currently a widely used communication interface in data acquisition and control applications where multiple nodes communicate with each other. Network topology is probably the reason why RS485 is now the favorite of the four mentioned interfaces in data acquisition and control applications.

Multiple receivers may be connected to such a network in a linear, multidrop 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. Because a mark (logic 1) condition is traditionally represented (e.g. in RS-232) with a negative voltage and space (logic 0) represented with a positive one, A may be considered the non-inverting signal and B as inverting. The sizing of the measurement system begins with knowing the main parameters of the plant; in particular, from the characteristics of the protection switch, the type of distribution system, the rated current, the rated voltage and the type of busbar can be known. This ensures maximum protection for the inner core. Noise is easily picked up and limits both the maximum distance and communication speed. However, it is important to note that as the length of the cable increases, signal distortion can occur during transmission along the communication line, thereby reducing the maximum data rate that can be achieved. Transformers can be of different types, depending on the assembly system: a through cable or a cable with a coiled primary, transformers for assembly on horizontal or vertical bars.

It requires minimal wiring and can share the wiring among several seats, reducing weight. RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. B- lines, representing a two-wire half-duplex configuration, which is the most commonly used wiring method in RS485. The two-wire half-duplex system enables bidirectional data transmission between two devices, but not simultaneously. This cable structure helps maintain stable data transmission in electrically noisy environments. RS-485 can send data 1200 meters on 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. RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. RS232, RS422, RS423 and RS485 are serial communication methods for computers and devices. In multifunction instruments, not only the cables connected to the measurement, but also the RS485 serial port and the analog and digital inputs and outputs must be wired.

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