Will need to have Checklist Of Rs485 Cable Networks > 자유게시판

Slave devices use the master in/slave out pin, MISO, for transmitting, and the master out/slave in pin, MOSI, for receiving data. It is NOT necessary to introduce long delays in a network to avoid "data collisions." Because delays are NOT required, networks can be constructed, that will utilize the data communications bandwidth with up to 100% through put. There are surface mount resistor pads on the QScreen that will allow you to bring out the secondary serial port to the Field Header on pins 5-6 or 7-8 as shown with the parentheses in Table 11-3. Pads are also available to bring out the RS485 signals to the DB9 Serial 1 Connector. Ideally, the two ends of the cable will have a termination resistor connected across the two wires. End of line termination resistor (120 ohm 1/4 watt) to be installed at both ends of network. All communication cabling to be installed in a daisy chain configuration, no T’s are permitted.

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). I recently bought some RS485 cable, it had two pairs, both had stripes. Users can utilize a longer cable, up to 1200 meters or 4000 feet. If on the other hand each terminal can accept only a single cable, a proper branch must be created using three auxiliary terminals for each instrument to be connected. At any given time, only the master and a single active slave communicate. The master initiates a communications request to a "slave node" by addressing that unit. The Serial 1 port can be configured for either RS232 or RS485 communications at up to 19200 baud. This helped RS485 become a widely used and very versatile form of serial communication. A Modbus RS485 connects a Master device to one or more Slave devices. In order to increase the extent of the Modbus network, repeaters can be used; and signal amplifying and regenerating devices provided with two communication ports that transfer to each what they receive from the other. For seven data bits with a parity bit, M would be cleared (equal to zero), and PE would be set in order to make the most-significant bit of a normal eight-bit byte be used by the serial port as a parity bit.

You might also consider operating the secondary serial port at a lower baud rate to relax the timing constraints. Each device has a communication port with two terminals, which are indicated for the sake of convenience as A and B. In these two terminals the communication cable is connected so that all the devices that take part in the communication are connected in parallel. It seems if there is a lot of RFI in the installation, shielded twisted cable can be justified. So is there a meaning to any of these? Is the striping set by manufacturers or have any meaning beyond indicating a pair? The RS485 system used for Modbus communication provides a main cable (Bus or backbone), to which all the devices have to be connected with branches (also known as stubs) that are as short as possible. Henceforth, we shall consider Slave devices to be measuring instruments with serial communication, even if the cabling is similar for all Modbus devices. The cabling of the industrial communication systems (Modbus RS485) is different in some ways from the cabling used for power cabling and the electrician may experience some difficulties if he is not an expert in Modbus communication networks.

In this case, cable connections may be made to Serial 1 on either the 10-pin Serial Communications Header or the Serial 1 Connector. In other words, each local UART on the wildcard can both send data to and receive data from a remote UART on the other end of a connecting serial cable. RS232’s greatest benefit is its universality; practically all personal computers can use this protocol to send and receive serial data. The most widely used protocol is RS232, a full duplex protocol with a single-ended bipolar voltage swing on the serial cable. In order to avoid signal reflections, a 120 Ohm termination resistance must be fitted on each end of the main cable. In order to avoid errors when many devices are connected, cables of the same colour should be used for all the connections to the terminals A and cables of the same colour should be used for all the connections to the terminals B of the various devices (e.g. white for A and blue for B). Be sure to use a wire pair such as the blue and blue/white pair for the data lines and a third wire or pair twisted together for the common connection.