Introduction and overview
1.2 Bus systems
3WL/3VL circuit breakers with communication capability - PROFIBUS
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System Manual, 03/2011, A5E01051353-02
Acyclic data transfer
Acyclic data transfer is implemented via DPV1. DPV1 adds several functions to the existing
PROFIBUS standard. These include reparameterization of the slave configuration during
operation, and the establishment of acyclic data traffic. With the help of DPV1, data can also
be read direct from the slave by a class 2 master, even though it still has a logical link to a
class 1 master. In physical terms, DPV1 transfer and DP standard transfer take place over
one line.
Acyclic data transfer is used, for example, in conjunction with operator control and
monitoring systems such as WinCC or configuration software like Switch ES Power (see
Chapter ). The PC used here with built-in PROFIBUS DP interface card then handles the
function as a class 2 master. From there, the data sets are transferred via DPV1 and the
new values are set, e.g. in the case of changing the value for the tripping current. However,
cyclic data exchange between the circuit breaker and the PLC continues.
1.2.2
Ethernet
Definition/standard
Industrial Ethernet is a powerful cell network in accordance with the IEE 802.3 (ETHERNET)
standard. Transfer rates up to 1 Gbit/s in conjunction with "Switching Full Duplex" and
"Autosensing" make it possible to adapt the required power in the system to the prevailing
requirements. The data rate can be selected to suit particular needs, as integrated
compatibility makes it possible to introduce the technology in stages. With a current market
share of over 80%, Ethernet is the most frequently used LAN in the world.
The benefits of Ethernet are as follows:
●
Ethernet is especially suitable for harsh industrial environments subject to
electromagnetic interference.
●
With the new technology of the Internet, Ethernet offers diverse options for global
networking.
●
With Industrial Ethernet, SIMATIC NET ® offers the means of using intranets, extranets
and the Internet - already available in the office area - in EMI-polluted production
processes and process automation.
Communication between peers
Ethernet is not designed on the master-slave principle like PROFIBUS DP. All nodes are
equal peers on the bus and each can transmit and/or receive.
A sender can only start transmitting on the bus if no other node is transmitting at that
moment. This is implemented by having each node "listen in" to determine if message
frames are addressed to it or if there is currently no active sender. If a sender has started
transmitting, the transmitted frame is checked for corruption. If the frame is not modified,
transmission is continued.
If the sender detects corruption in its data, another sender must have started before it, and
both nodes terminate transmission. The sender restarts transmission again after a random
time.