GE GFK-1541B - Manual (Page 11)

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