For example, Belden 3105A cable can be specified, but different types of cable with equivalent characteristics can be used. The cable to be used is a shielded twisted pair (telephone type). A higher number introduces excessive delays in the communication system. The maximum number of repeaters that should be serially connected is 3. Using a repeater, the main cable is divided into different segments, each of which can be up to 700 m in length and connect 32 devices (this number includes the repeaters). Moreover, each segment of the network must be connected to the terminator.
MODBUS RTU WIRING DRIVERS
If the distance segment exceeds 1200 m or the number of drivers in the segment more than 32 pieces, you should use a repeater (repeater), to create the next segment. 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. The maximum number of devices that can be connected to a main cable is 32, including the Master. The main cable must be no longer than 700 m! This distance does not include the branches (which must nevertheless be short). Maximum distance and maximum number of devices
Network with Bus structureįigure 2 – Examples of incorrect Bus connectionsģ. The branches must be no longer than 1200 m! Longer branches could cause signal reflections and generate disturbances and consequent errors in the reception of data.įigure 1 shows an example of a correct Bus connection. 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. Unlike what happens in many energy distribution systems, the manner in which the devices are connected in parallel is important. The communication port on the Master device, whatever it is, has two terminals that correspond to A and B. This makes it easier to identify cabling errors. 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. E.g.Inverting the ‘A’ and ‘B’ connections of a device does not only prevent it from communicating but may also stop the entire communication system from working owing to incorrect direct (polarisation) voltage found on the terminals of the incorrectly connected device.
MODBUS RTU WIRING SERIAL
As a master gateway, up to 248 UID’s are addressable per master gateway configured serial ports.Both Modbus RTU and ASCII forms of the Modbus protocol are supported.