Ethernet Communications Modules, 3rd Edition, Rev. D
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Chapter 2: Setup and Installation
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Maximum Number of ECOM Modules on the Network
The maximum number of nodes that can be connected to a 10/100BaseT or 10BaseFL network
is a function of the topology used in constructing the network. Therefore, it is not possible to
state an absolute maximum number of nodes that would apply in all cases.
The IEEE 802.3 specification defines the maximum node limit for an Ethernet segment in
terms of the ability to detect and avoid data collisions. A “legal” network can have any number
of devices provided that they can:
• Detect all data collisions that may occur during the communication process and
• Respond to these collisions appropriately.
You must take into consideration the network limitations imposed by all cabling and network
devices. Consider the limitations imposed on your network if your network uses:
• A combination of cabling standards, such as 10/100 BaseT and 10Base2, or
• Intermediate devices, such as switches or routers.
Each ECOM module can be assigned a Module ID ranging from 1 to 999,999,999.
Theoretically, you could have this many Ethernet modules coexisting on a single network. Other
network limitations would restrict the network size before reaching this limit. For the majority
of network PLC applications there is practically no limit to the number of ECOM modules
you can access from the NetEdit3, DirectSOFT Programming Software or the KEPDirect for
PLCs software.
There is a node limit for PLC-to-PLC communications. The network Read and Write
instructions performed by the initiating (master) PLC are only capable of accessing PLCs with
Module IDs of 1 through 90. This effectively sets the maximum number of nodes available for
PLC-to-PLC communications at 90.
WARNING: We recommend against connecting Ethernet modules to the same network that serves as your
primary office network. While Ethernet networks can handle a very large number of data transmissions,
and normally handle them very quickly, heavy Ethernet traffic can adversely affect the reliability and
speed of the network.
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