Rockwell-automation 1766-Lxxxx MicroLogix 1400 Programmable Controller User Manual download pdf (Page 372)

332 Rockwell Automation Publication 1766-UM001H-EN-P - May 2014

Appendix G Connecting to Networks via Ethernet Interface

Ethernet Connections

TCP/IP is the mechanism used to transport Ethernet messages. On top of TCP,

Ethernet/IP and/or Modbus TCP protocol is required to establish sessions and

to send the MSG commands. Connections can be initiated by either a client

program (RSLinx application) or a processor.

The client program or processor must first establish a connection to the

MicroLogix 1400 to enable the MicroLogix 1400 to receive solicited messages

from a client program or another processor.

In order to send an outgoing message, the MicroLogix 1400 must first establish a

connection with the destination node at a specified IP address on the Ethernet

network. A connection is established when a MSG instruction executes and no

previous connection exists.

When a MSG instruction executes, the MicroLogix 1400 checks to see whether a

connection has been established with the destination node. If a connection has

not been established, the MicroLogix 1400 attempts to establish a connection of

the peer type.

In order to receive messages from another device on Ethernet, an “incoming”

connection must be established. This incoming connection is made by the

sending processor and uses one incoming connection in the receiving processor.

TIP

The most common wiring for RJ45 cables is the "straight through"

cable which means that pin 1 of the plug on one end is connected to

pin 1 of the plug on the other end. The straight through RJ45 cable is

commonly used to connect network cards with hubs on 10Base-T and

100Base-Tx networks. On network cards, pair 1-2 is the transmitter,

and pair 3-6 is the receiver. The other two pairs are not used. On hubs

pair 1-2 is the receiver and 3-6 the transmitter. It may be best to wire

your cables with the same color sequence. In this cable layout, all

pins are wired one-to-one to the other side. The pins on the RJ45

connector are assigned in pairs, and every pair carries one differential

signal. Each line pair has to be twisted.

In small networks where only two Ethernet devices need to be

connected together point-to-point, a "cross over" RJ45 cable may be

necessary, where the transmit and receive lines on both JR45

connectors are cross connected. The color coding for the cross over

RJ45 cable have been defined in the EIA/TIA 568A standard. In a

cross-over cable layout, you should remember that one end is normal,

and the other end has the cross-over configuration.

However, because the MicroLogix 1400 Ethernet port implements

"auto-crossover" (also called Automatic MDI/MDI-X Configuration), a

straight through cable may be used even for direct point-to-point

connections between the MicroLogix 1400 and another Ethernet

device.

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