- Transmission rate required for the task (only one uniform transmission rate can be used in any one network).
- Required number of nodes.
- Type of network components required (bus terminals, bus connectors, plug-in connecting cables).
- Bus cables that are to be used.
- Segment lengths desired.
- Electromagnetic and mechanical environment of the cables (e.g. overvoltage protection, cable ducts).
- Number of RS485 repeaters between any two terminal devices is limited to a maximum of 9.
- In the case of extensive structures with repeaters there are longer transfer times which must be taken into account where appropriate when configuring the network.
Configuring electrical networks with RS485 repeaters:
- To increase the number of nodes (>32) in a network or increase the cable lengths between two nodes you can connect segments into a network using RS485 repeaters. Fig. T-1 shows a possible combination of several segments connected in a network using repeaters.
- The RS485 repeaters support all transmission rates from 9.6 kbit/s to 12 Mbit/s.
Fig. T-1 (1 terminator activated)
The following conditions must be met when configuring an electrical network with RS485 repeaters:
- You must keep to the maximum segment length specified for a transmission rate.
- The maximum of bus couplings (nodes, RS485 repeaters, OLMs) on one segment is limited to 32. Other restrictions are possible with the transmission rate of 1.5 Mbit/s.
- The maximum number of nodes in one network is limited to 127.
- A maximum of 9 RS485 repeaters can be installed between two nodes.
The system response time of a PROFIBUS network depends decisively on
- The system version (mono- or multi-master system).
- The maximum response time of each individual bus node.
- The volume of data to be transferred.
- The bus configuration (topology, cable lengths, active network components).
Adapting the bus parameters to the PROFIBUS network concerned (configuration) is done using configuration software such as COM PROFIBUS or STEP 7.
Because of message delays through cables and network components as well as through monitoring mechanisms in the network components, when configuring you must adapt the PROFIBUS network parameter "Slot time" to the network size, the network topology and the transmission rate.
More information is available in the manual in Entry ID 1971286.