Omron Ethernet Guide


Omron PLCs can support Ethernet connections in a variety of ways:

When connected to an Ethernet network the Factory Intelligent Network Service (FINS) protocol is used to communication with Omron PLCs. The FINS protocol can be used in one of two ways:

The remainder of this article describes how Omron FINS works over UDP/IP and TCP/IP.

Omron FINS over UDP/IP

When communicating with Omron PLCs using UDP/IP, the messages sent to the PLC will contain both Internet Address and FINS Address information:

Address FieldProtocolDescription
Target IP Address IP The target IP address in the IP header
Source IP Address IP The source IP address in the IP header
Target UDP Port UDP The target port number in the UDP header
Source UDP Port UDP The source port number in the UDP header
Destination FINS Network FINS The destination FINS network number
Source FINS Network FINS The source FINS network number
Destination FINS Node FINS The destination FINS node number
Source FINS Node FINS The source FINS node number

When an inbound message arrives at the Ethernet interface, Omron PLCs use the Destination FINS Network and Destination FINS Node numbers to route the message to the correct destination. The destination could be the local CPU unit or another PLC connected on a separate network. When the destination responds it will use the Source FINS Network and Source FINS Node numbers to route the reply message back to the Ethernet interface that received the message.

Diagram of FINS node to IP Address Translation

The important point to understand is the IP Addresses and Port numbers are not forwarded as part of the internal communications, so when the reply arrives back at the Ethernet interface, the Ethernet interface needs a way of translating the destination FINS Node address back into an IP Address and UDP Port Number.

Omron Ethernet Interfaces provide up to four methods to map the destination FINS node address to the correct IP Address and UDP Port number:

ConversionRemote IP AddressRemote UDP Port Number
Automatic (dynamic) The IP Address from the inbound message is automatically added to a table mapping FINS node number to IP Address. The UDP Port Number from the inbound message is automatically added to a table mapping FINS node number to UDP Port Number.
Automatic (static) The network portion of the IP Address of the Ethernet interface combined with the FINS node number. Same as the FINS/UDP Port of the Ethernet interface. The default port number is 9600.
IP Address Table A manually configured table mapping FINS node number to IP Address. Same as the FINS/UDP Port of the Ethernet interface. The default port number is 9600.
Combined The IP Address Table lookup is attempted first. If the IP Address Table lookup fails, the Automatic method is tried.

Automatic (Dynamic) Conversion

In Automatic (Dynamic) Conversion, the Ethernet Interface listens to inbound messages and automatically populates a table mapping FINS node number of destination IP Address and Port number.

This is the easiest conversion method to use, but does mean the PLC will accept communications from any external source.

This mode is not supported on the older Ethernet Interface modules: CJ1W-ETN11, CS1W-ETN11 and CS1W-ETN01.

Automatic (Static) Conversion

Automatic (Static) conversion replaces the node number of the Ethernet module's IP address with the destination FINS node number using this operation:

(EthernetUnit IP AND NetworkMask) OR DestinationFINSNodeNumber

Examples of automatic Omron FINS Node Number to IP Address translation:

Ethernet Unit
IP Address
IP Network MaskDestination
FINS Node Number
IP Address

Note: If the IP Network Mask specifies more than 8 bits for the node number, some of the destination IP Addresses will be inaccessible. For example, if the IP Network Mask is, IP Addresses where either of the two middle numbers are non-zero would not be accessible.

IP Address Table Translation

In IP Address Table mode, the destination IP address is looked up from an address table configured in the Ethernet module. For example:

FINS NodeIP Address

Messages for FINS node 20 would be sent to, and messages for FINS node 25 would be sent to

Combined Translation

In Combined Translation mode, the destination FINS node number is first looked up in the IP Address Table. If the lookup does not find an IP Address, the Automatic method is used.

Omron FINS over TCP/IP

Omron FINS over TCP/IP uses a lookup table to translate between the FINS Network and Node addresses and the corresponding TCP/IP connection.

The lookup table is a fixed size, which limits the number of connections allowed to the PLC. For example the CJ1W-ETN21 Ethernet module has a lookup table of 16 entries supporting 16 simultaneous connections, but The CP1W-CIF41 option module has a lookup table of 2 entries, supporting 2 simultaneous connections.

After establishing a TCP/IP link to the PLC, the client program will typically exchange FINS node addresses with the PLC which sets up an entry in the lookup table. Once the connection is set up the client program can exchange FINS messages with the PLC.

Further Information

Omron CS/CJ Ethernet Setup Guide

For information about configuring CS/CJ PLCs with Ethernet communications.

Omron Driver

For information about the Omron Driver.


For definitions of the terms used in Fernhill SCADA.