BACnet MSTP Installation, RS485 and Cables > 고객센터

In no event will OPAL-RT TECHNOLOGIES or its direct or indirect suppliers be liable for any damages whatsoever including, but not limited to, direct, indirect, incidental, or consequential damages of any nature including, without limitation, loss of business profits, data, business information, or any and all other commercial damages or losses, or for any damages in excess of the list price for the license to the software and documentation. OPAL-RT TECHNOLOGIES makes no representation or warranty with respect to the adequacy or accuracy of this documentation or the software which it describes. The QVGA Controller offers a unique addition to full duplex RS232: it can place its RS232 transmitter into a high impedance silent mode under software control. The RS485 is also a form of serial communication faster than RS232. It provides a convenient means of connecting the QVGA Controller to a variety of peripheral devices, including analog to digital and digital to analog converters, real time clocks, and other computers which use high speed communication. 2. Always connect the ground reference conductor first if you are connecting a device that is powered up or you are connecting your laptop to an operating network. Connecting computers together in multi-drop networks is common in factories and laboratories.

One common example that many people probably know that is a computer connected to a printer, the RS232 is widely used for printers in working places. It is a common reference signal. It is his reference to Art that makes RS485 bad. RS485 specifies a 2-wire, half-duplex communications bus. When a slave is addressed, it executes RS232Transmit() at which point full duplex (two-way) communications commences between the master and the selected slave. To use two wires ( as opposed to full duplex 4 wire) for RS485 each devices transmitter and receiver must be set to an idle state to release the line for others use. 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 greatest feature of RS485 is the fact that you can connect up to 32 devices on one system. The RS232 protocol allows the system or computer to give commands to the printer via a voltage signal, then the printer receives the commands and completes the print.

A three-post jumper located between the third socket and H6 configures the primary serial port for either RS232 or RS485 operation. The RS485 standard is based on 32 devices. The historical data serves to meet an American Petroleum Institute (API) industry standard for how data should be stored. While these signals provide a data path, they do not provide hardware handshaking that allows the two communicating parties to let each other know when they are ready to send or receive data. The RS232 protocol specifies the use of two separate grounds, a signal ground and a protective (or "chassis") ground. An "Automatic Converter" (RS232 to RS485) will turn on the RS485 transmitter when data is detected on the RS232 port, and revert back into the receive mode after a character has been sent. If a star configuration is unavoidable, special RS-485 repeaters are available which bidirectionally listen for data on each span and then retransmit the data onto all other spans.

Another big culprit are Variable Frequency Drives. Modbus ASCII messages are framed by a leading colon (":") and trailing newline (CR/LF). Modbus protocol itself provides no security against unauthorized commands or interception of data. It can only transmit/receive data serially, so it first converts the parallel data into serial data and then transmits the data. Routines that temporarily disable interrupts for significant periods of time can also interfere with the Serial2 port. When full-duplex is converted into half-duplex only one device at a time can transmit data. A clue to knowing if you selected one is to look at the cables Nominal Impedance. Look for UL on the data sheet. A slave will never transmit any data or perform any action without a request from the master, what is rs485 cable and slaves cannot communicate with each other. It receives bytes sent by a slave device via the "master in/slave out" pin, MISO. When you install it in the full network other devices or this device stops working properly. Since the standard was developed most RS485 chips present less than the full unit load originally specified.