Rockwell Automation T8xxx Trusted Communications Interface - Manual (Page 56)

Trusted
TM
Communication Interface T8151B
Issue 21 Apr 10 PD-T8151B 56
6.3. Ethernet – 10Base2
10Base2 Ethernet is a linear network with nodes fitted along the length of one network; it cannot cope
with spurs. The connections use 50 Ohm coax cables (e.g. RG58). The rules for connecting 10Base2
Ethernet are given below.
 The maximum length of a segment without repeaters is 185m.
 A maximum of 4 repeaters are allowed to extend a segment, where the cable length between
the repeaters is less than or equal to that of a non-repeated cable segment and 2 segments
must be links only (i.e. no connections apart from the 2 repeaters).
 The maximum number of nodes on a segment is 30 and includes any repeaters.
 There should be a minimum of 0.5m between nodes.
 Each cable segment must be terminated at either end with a 50R termination.
 The connections to each device must be by T-connectors directly onto the BNC jack provided.
A spur from the network to the device will cause reflections in the cabling and stop the network
working correctly.
 The screen of a segment may be earthed for safety reasons if required, but only at one point
on the segment.
 If connecting to a Communication Interface via the Interface Adapter, the T-connection must
plug directly into the BNC jacks on the bottom of the unit.
 If wiring a connector directly onto the back of the Communications Interface DIN41612
connector, keep the lead to the BNC jack as short as possible, i.e. just long enough to come
out of the backshell and no longer (The Ethernet standard recommends no more than 4cm).
Note that 10Base2 is not available on Communications Interface modules after build C.
6.4. Ethernet – 10BaseT/100BaseT
The 10BaseT/100BaseT Ethernet connections normally use unshielded twisted pair cable (EIA
Category 3 (‘Cat3’) or better for 10BaseT and ‘Cat5’ for 100BaseT). The standard connector is the 8
pin RJ45 jack. The rules for connecting 10BaseT Ethernet given below.
 10/100BaseT Ethernet is a ‘star’ network. A point to point link between two nodes may be
made with a single cable. Multiple nodes require a central device to connect nodes together. A
hub relays data packets to all nodes. A switch intelligently routes data packets only to the
intended recipient.
 The maximum length of a (copper) segment is 100m with the cable grades listed above.
Longer distances are usually converted to fibre.
 Only use twisted pair cable. Non twisted pair can degrade network performance severely.
When connecting equipment to a hub or switch, use a standard straight (pin to pin) cable. If connecting
equipment together (e.g. Communication Interface directly to a PC, or PC to PC) then a crossover
cable is required. A crossover cable is sometimes also required to connect two hubs/switches if they
do not auto-detect the connection, and some devices have a selection switch.
Note: the Ethernet standard states that hub/switch ports that are internally crossed over (and therefore
only need straight cables) should be marked with an ‘x’.
The Communication Module Ethernet ports do not auto-detect the cable wiring, as switches do. This
may result in problems if both ends drive the same cable pair, because the drivers can latch up and fail
to recover, requiring a restart of the CI module and Ethernet device. The switch may also not auto-
sense the difference if the cable type is changed.