Lenze PLC Designer PLC Designer (R3-1) - Manual (Page 114)

L-force | PLC Designer
Concepts and Base Components
112 DMS 4.1 EN 03/2011 TD29
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Thereon a node may handle data packets in a correct way:
• If the target address equals the address of the current node, it is determined as
receiver.
• If the target address starts with the address of the current node, the packet is
intended for a child or descendant of the node and has to be forwarded.
• Else, the receiver is no descendant of the current node. The packet has to be
forwarded to the own parent.
Relative addressing is a special feature. Relative addresses do not contain the node
number of the receiver node, but directly describe the path from the sender to the
receiver. The principle is similar to a relative path in the file system: The address is
comprised of the number of steps the packet has to move “up”, i.e. to the next
respective parent, and the subsequent path down to the target node.
The advantage of relative addressing is, that two nodes within the same subtree are
able to continue the communication when the entire subtree is moved to another
position within the overall control network. While the absolute node addresses will
change due to such a relocation, the relative addresses are still valid.
Determination of addresses
The knowledge about the own address demands from a node the knowledge either on
the address of the parent or on being a top-level node. For this purpose a node will
send an address determination message as broadcast to its main network during boot-
up. As long as this message is not responded, the node considers itself to be a top-
level node, although it will continue to try and detect a parent node. A parent node will
respond by an address notification. Thereon the node will complete its own address
and pass it to the subnets.
Address determination can be executed at bootup or on request of the programming
PC.
Not yet implemented: Once the address of a node is frozen, address determination
can no longer be executed.
3.11.4 Structure of addresses
Below you find a detail description on the structure of the following address types:
• Network adresses
• Node addresses
• Absolute and relative addresses
• Broadcast addresses
Network addresses
Network addresses represent a mapping of addresses of a network type (e.g. IP
addresses) to logical addresses within a control network. This mapping is handled by
the respective block driver. Within an EtherNet with Class C IP addresses, the first 3
bytes of the IP address are the same for all network devices. Therefore, the last 8 bits of
the IP address suffice as network address, since they allow unambiguous mapping
between the two addresses at the block driver.