My Greatest What Is Rs485 Cable Lesson > 자유게시판

Up to 32-nodes (drivers and receivers) are allowed on one multi-drop, bi-directional network. Here are the detailed specifications of RS485. Commercial aircraft cabins also use RS485 for low-speed data communications. If your application requires use of the secondary serial port as well as other interrupt routines, the key is to keep the interrupt service routines short and fast. R.E.Smith also provides an extensive line of optical/transformer isolated repeaters and multi-port repeaters as well as a series of fiber optic products which provide very high isolation. This cable is usually 24AWG. Category-5 cable will generally work well in most instances even though its characteristic impedance is 100 Ohms. In general RS485 is designed for multi-drop, "daisy-chain" operation over a single twisted pair cable with a nominal characteristic impedance of 120 Ohms. Converters in general can be used to change the electrical characteristice of one communications standard into another, to take advantage of the best properties of the alternate standard selected.

In general it is very important not to run communications wires in the same trough or conduit or in parallel with AC power cables. Because they are produced in such large quantities, Cat 5 cables are relatively inexpensive, often less than half the price of specialty RS-485 cabling. The primary and secondary serial communications ports are accessible through the QVGA Controller's 10 pin, dual row Communications Connector (H14) and through the individual Serial 1 and Serial 2 connectors. RS485 is another protocol supported by the primary serial port on the QVGA Controller. We can gain insight into the operation of the RS232 protocol by examining the signal connections used for the primary serial port in Table 11 5. The transmit and receive data signals carry the messages being communicated between the QVGA Controller and the PC or terminal. If you have not yet compiled the GETSTART program and you want to do the exercises here, open GETSTART.C in your TextPad editor, click on the Make Tool (the Make icon), and after the compilation is done, enter the Terminal Program by clicking on the terminal icon and use the "Send Text File" menu item to send GETSTART.DLF to the QVGA Controller.

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. 5-Year Full Parts Replacement or Full Product Replacement Prorated Warranty from the date of purchase. This allows you to configure full duplex multi-drop networks in which a single master can sequentially address one of many slaves and start a full-duplex exchange of data. Thus RS485 is the standard protocol of choice when multi-drop communications are required. The RS485 standard addresses the problem of data transmission, where a balanced (differential) transmission line is used in a multi-drop (party line) configuration (or point-to-point if only two devices are on the network). You can easily enjoy the advantages such as low power consumption and long transmission range, without affording the cost of changing the sensors you are using. Ideally, the two ends of the cable will have a termination resistor connected across the two wires and two powered resistors to bias the lines apart when the lines are not being driven. While it goes against conventional wisdom, and can potentially cause a problem with circulating currents by grounding a shielded cable at both ends, what is rs485 cable this method is very effective at keeping induced lightening noise away from the communications lines.

With galvanic isolation the damage is generally limited to only one leg of the network, except in extreme cases of very high voltage (induced by lightening for example). By "isolating" sections of a large network, the accumulated noise on one isolated leg is not so likely to cause a data error that will propagate to another leg of the network. Once an RS485 network exceeds about 32 nodes on a network, serious consideration should be given to using galvanic isolation. A typical RS485 network can operate properly in the presence of reasonable ground differential voltages, withstand driver contentious situations, provide reliable communications in electrically noisy environments (good common mode rejection using twisted pair cable, shielding provides additional protection), and support thirty-two or more (many IC manufacturers have 1/2, 1/4, 1/8 unit load devices) drivers and receivers on the line. In addition there is no good way to add terminations resistors at the ends of a "star" network.