GE GFK-1541B manual 90-30 CPU374

1

Special Considerations for Ethernet Interfaces with Embedded Switches

Ethernet Interfaces that incorporate embedded switches (only the Series 90-30 CPU374) provide some additional connection options and have some additional installation and operation considerations.

These Ethernet Interfaces provide two RJ-45 connectors on the front of the module. It is important to realize that there is only one interface to the network (only one Ethernet address and only one IP address) provided by these Ethernet Interfaces. The two connectors allow up to two Ethernet devices (hubs, switches, other PLCs, PCs) to be connected to the Ethernet Interface. This arrangement is diagrammed below.

90-30 CPU374

Ethernet

Processor

Ethernet

MAC

10/100 Network

Switch

Port 1

Port 2

For simple installations, the embedded switch allows PLCs and other devices to be connected together without requiring any additional components.

Operator Interface

PLC

PLC

Personal Computer

It is also possible to daisy-chain PLCs together without additional components, but that should be done with great care. In designing a system, remember that a loss of power or reset on any Ethernet Interface in a daisy chain will cause loss of communications with all devices downstream from the lost module.

The second port, if left unused, can be used to plug in a programmer over Ethernet.

Caution

The two ports on the Ethernet Interface must not be connected, either directly or indirectly, to the same device. The hub or switch connections in an Ethernet network must form a tree, otherwise duplication of packets may result.

1-6 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual– May 2002 GFK-1541B