Rockwell Automation T8xxx Trusted Communications Interface - Manual (Page 57)

Trusted
TM
Communication Interface T8151B
Issue 21 Apr 10 PD-T8151B 57
Table 22 below shows the cable wiring for the 10/100baseT Ethernet connections on the
Communications Interface. The table shows both crossover and straight connections:
From To
DIN41612 Interface
Adapter Straight Crossover
Plug (PL5) RJ45 Plug RJ45 Plug RJ45 Plug
J6
A21 (TD+1) 1 (TD+) 1 (TD+) 3 (RD+)
B21 (TD-1) 2 (TD-) 2 (TD-) 4 (RD-)
A22 (RD+1) 3 (RD+) 3 (RD+) 1 (TD+)
B22 (RD-1) 6 (RD-) 4 (RD-) 2 (TD-)
J8
A25 (TD+2) 1 (TD+) 1 (TD+) 3 (RD+)
B25 (TD-1) 2 (TD-) 2 (TD-) 4 (RD-)
A26 (RD+1) 3 (RD+) 3 (RD+) 1 (TD+)
B26 (RD-1) 6 (RD-) 4 (RD-) 2 (TD-)
Notes:
TD+ and TD- should be connected as one twisted pair, RD+ and RD- as the other.
Pins 4,5,7 and 8 of the RJ45 are unused on 10/100BaseT applications although a number of ready made cables have the
connections made.
Table 22 10/100baseT Ethernet Connections
6.4.1. General Notes
Ethernet connections can be extended in a number of ways in order to build larger networks or travel
greater distances. With the correct repeaters, it is possible to mix different transmission media on the
same network. For example, the Communication Interface cannot communicate at 1000 Mbits/s or
connect to fibre but it can be connected via an Ethernet switch to these networks.
There are a number of issues involved in building multiple segment and mixed media networks that are
beyond the scope of this document. Further information can be found in the Ethernet standards.
Although Ethernet communications is ubiquitous in industrial and office networks, it is recommended
that safety-related communications (and any industrial communications considered critical to
production) is kept separate from general office communications because the load on the general
network due to office communications will be unpredictable.
6.4.2. Network Reflections
If two networks are connected together via a router or some other method which allows packets to
transfer between the networks, it is possible for one network to pass the data to the second and then
the second network to pass the data to the first network knowing that the first network contains that IP.
If this happens, the same data will bounce back and forth between the networks. Most data packets
have a transfer count limit (‘time to live’) of 32, 64 or 128 transfers. For example, if it is set to 32 it will
only go through 32 routers and then the packet will be discarded. If each network has 1 router and the
networks are connected together, every data packet sent to a particular communication interface
module will arrive at the module 16 times and hence require 16 times the processing. If is set to 128, it
will give 64 times the loading. This problem is made worse when a switch or any other connection
sends a broadcast message (e.g. updating its IP connection table). This will bounce to all nodes at
least 16 times on top of the normally traffic x 16. The TTL (time to live) cannot be controlled by the
application and it may even be a router broadcast packet that is causing the problem.