What is RS485 and how is it used in Industrial Control Systems? > 자유게시판

Owing to hardware constraints, if modem handshaking is needed on UART channel 1, then channel 1 must be configured for RS232, and channel 2 cannot be configured for RS232 communications. These factors are discussed in more detail in The UART Wildcard: Modem Handshaking Signals. A Modbus RS485 connects a Master device to one or more Slave devices. Now there was certain instances I used STP wire for rs485 because I had a lot of devices connected in a long run chain (DMX512 lighting fixtures). It seems if there is a lot of RFI in the installation, shielded twisted cable can be justified. I tried connecting it directly to the computer either with a normal network cable or with a crossover cable but the web page doesn't open. Display and configure video; control PTZ; test cables, audio, IP network connections, PoE voltage; and power 12VDC cameras. Power cameras and review the display without the hassle of running between the camera and a DVR located in a separate area.

Ensure power and data lines are connected properly and there are no loose connections. We found that there are 10K ohm resistors fitted on the A & B data lines with the A channel having a 10K pull-up resistor to 3.3 volts and the B channel having a 10K pull-down resistor to ground. Note that the local and the remote must share a common ground, so a minimum of 3 wires are required for full duplex RS232 communications: a transmit wire, a receive wire, and a common ground. One very common example in the automation world is remote control of VFDs or Variable Frequency Drives. Common telephone cable is often twisted. Sometimes it is necessary to transmit over longer distances, rs485 cable or to run networks with spurs off the main cable run. The main cable must be no longer than 700 m! Both the local and remote UARTs must be configured for the same communications parameters.

The cable shield must be earthed only in one point. The resulting signal levels on the interface cable connect the local and remote in a manner specified by a standard protocol. A RS232 - RS422 converter is a 4-wire, full-duplex, differential protocol with multi-drop capabilities and a recommended distance limit of 4000ft. ANSI/TIA/EIA-422-B is the American national standard for the RS422 protocol. However since only a true RS485 network can have addressable serial RS485 devices, the RS232 converter needs to be addressable either by software or by DIP switches when using it in this type of configuration. Use a 485 to USB serial cable, connect it to the interface of the 485 device and the computer's USB port, assign a COM port on the computer, open serial debugging assistant software, set the serial port parameters consistently, input the corresponding COM port, and monitor the data from the 485 device. Even better is Ethernet cable, because it is twisted and often shielded. If you use a twisted pair cable, make sure to use the same twisted pair for A and B, but use another twisted pair for GND.

RS485 uses the same differential signaling scheme as RS422, and hence has the same superior signal-to-noise characteristics and range described above. RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422. We tried several RS485 Pi hats, but all had the same issue. Problem solved thanks to RS485 communications. In fact, a single driver chip on the UART Wildcard is used to implement both RS422 and RS485 communications for a given serial channel. The serial data stream at the UART is conditioned by serial driver chips that transmit and receive the data. Question:What should I do if I can't receive data and the communication is abnormal? The maximum number of repeaters that should be serially connected is 3. A higher number introduces excessive delays in the communication system. Both protocols (or communication languages) are built into the instrument’s firmware and are user selectable.