Field Bus Interfaces¶
The Ethernet Communication Module has 2 RJ45 interfaces:
| 1 | TxD+ | Transmit Data + | |
| 2 | TxD- | Transmit Data - | |
| 3 | RxD+ | Receive Data + | |
| 4 | NC | not used | |
| 5 | NC | not used | |
| 6 | RxD- | Receive Data - | |
| 7 | NC | not used | |
| 8 | NC | not used | |
| Shield | Cable Shield | Functional earth |
The supported protocols and used Ethernet ports can be found in the description of AC500 Ethernet Protocols and Ports Supported Ethernet Protocols and PortsEthernet Protocols and Ports: Supported Ethernet Protocols and Ports
Communication via Modbus TCP/IP is described in detail in Communication with Modbus RTU and Modbus TCP/IP Communication \ with Modbus® RTU and Modbus® TCP/IPModbus Communication: Communication \ with MODBUS RTU
Cable Length Restrictions
For the maximum possible cable lengths within an Ethernet network various factors have to be taken into account. So, for twisted pair cables (TP cables) are used as transmission medium for 10 Mbit/s Ethernet (10Base-T) as well as for 100 Mbit/s (Fast) Ethernet (100Base-TX). For a transmission rate of 10 Mbit/s, cables of at least category 3 (IEA/TIA 568-A-5 Cat3) or class C (according to European standards) are allowed. For Fast Ethernet with a transmission rate of 100 Mbit/s, cables of category 5 (Cat5) or class D or higher have to be used. The maximum length of a segment which is the maximum distance between two network components is restricted to 100 m due to the electric properties of the cable.
Furthermore, the length restriction for one collision domain has to be observed. A collision domain is the area within a network which can be affected by a possibly occurring collision (i.e. the area the collision can propagate over). This, however, only applies if the components operate in half duplex mode since the CSMA/CD access method is only used in this mode. If the components operate in full duplex mode, no collisions can occur. Reliable operation of the collision detection method is important which means that it has to be able to detect possible collisions even for the smallest possible frame size of 64 bytes (512 bits). But this is only guaranteed if the first bit of the frame arrives at the most distant subscriber within the collision domain before the last bit has left the transmitting station. Furthermore, the collision must be able to propagate to both directions within the same time. Therefore, the maximum distance between two ends must not be longer than the distance corresponding to the half signal propagation time of 512 bits. Thus, the resulting maximum possible length of the collision domain is 2000 m for a transmission rate of 10 Mbit/s and 200 m for 100 Mbit/s. In addition, the bit delay times caused by the passed network components have also to be considered.
The following table shows the specified properties of the respective cable types per 100 m.
| Parameter | 10Base-T [10 MHz] | 100Base-TX [100 MHz] |
|---|---|---|
| Attenuation [dB / 100m] | 10.7 | 23.2 |
| NEXT [dB / 100m] | 23 | 24 |
| ACR [dB / 100m] | N/A | 4 |
| Return loss [dB / 100m] | 18 | 10 |
| Wave impedance [Ohms] | 100 | 100 |
| Category | 3 or higher | 5 |
| Class | C or higher | D or higher |
TC Cable
The TP cable has eight wires where always two wires are twisted to one pair of wires. Different color codes exist for the coding of the wires where the coding according to EIA/TIA 568, version 1, is the most commonly used. In this code the individual pairs are coded with blue, orange, green and brown color. While one wire of a pair is single-colored, the corresponding second wire is colored alternating with white and the respective color. For shielded cables it is distinguished between cables that have one common shielding around all pairs of wires and cables that have an additional shielding for each pair of wires. The following table shows the different color coding systems for TP cables:
| Pairs | EIA/TIA 568 Version 1 |
EIA/TIA 568 Version 2 |
DIN 47100 | IEC 189.2 | ||||
|---|---|---|---|---|---|---|---|---|
| Pair 1 | white/blue | blue | green | red | white | brown | white | blue |
| Pair 2 | white/orange | orange | black | yellow | green | yellow | white | orange |
| Pair 3 | white/green | green | blue | orange | grey | pink | white | green |
| Pair 4 | white/brown | brown | brown | slate | blue | red | white | brown |
Two general variants are distinguished for the pin assignment of the normally used RJ45 connectors: EIA/TIA 568 version A and version B where the wiring according to EIA/TIA 568 version B is the most commonly used variant.
Pin assignment of RJ45 sockets
A direct connection of two terminal devices is the simplest variant of an Ethernet network. In this case, a so-called crossover cable (also called crossconnect or crosslink cable) has to be used to connect the transmission lines of the first station to the reception lines of the second station. The following figure shows the wiring of a crossover cable.
Wiring of a crossover cable
For networks with more than two subscribers, hubs or switches have to be used additionally for distribution. These active devices already have the crossover functionality implemented which allows a direct connection of the terminal devices using 1:1 cables.
Wiring of a 1:1 cable
Caution
:strong:Risk of communication faults!
Malfunctions in communications may happen when using inappropriate cables.
Use only network cables of the categories 5 (Cat 5, Cat 5e, Cat 6 or Cat 7) or higher within PROFINET® networks.