Omron Ethernet Guide

Introduction

Omron PLC Devices can support Ethernet connections in different ways:

Some compact PLC Devices have a built-in Ethernet port, for example the CP1L-EL20DT1-D.
Compact PLC Devices without an Ethernet port, can be fitted with the CP1W-CIF41 Ethernet option board.
Some modular and rack mounted CPU units have a built-in Ethernet port, for example the CJ2M-CPU35.
Modular and rack mounted PLC Devices can be fitted with an Ethernet module, for example the CJ1W-ETN21.

When connected to an Ethernet network the FINS protocol is used to communication with Omron PLC Devices. The FINS protocol can be used in one of two ways:

FINS/UDP. Supported by all Ethernet connection types.
FINS/TCP. Not supported on some earlier Ethernet modules, for example the CS1W-ETN11.

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

Omron FINS over UDP

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

Address Field	Protocol	Description
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 a message is received by the Ethernet interface, these parameters are used to route the message to its destination:

Destination FINS Network
Destination FINS Node

The destination could be the local CPU unit or another PLC connected on a separate network.

When the destination replies, these parameters are used to route the message back to the Ethernet interface:

Source FINS Network
Source FINS Node

This diagram shows the message flow:

Diagram of FINS node to IP Address Translation

The important points to understand are:

The IP Address and Port number are not forwarded as part of the internal communications.
The reply arrives back at the Ethernet interface without this information.
The Ethernet interface needs a way of translating the destination FINS Node address back to 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:

Conversion	Remote IP Address	Remote 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.
The messages are used to populate a table mapping FINS node number to 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 sets part of the IP Address of the Ethernet module 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 Mask	Destination FINS Node Number	Destination IP Address
192.168.1.54	255.255.255.0	5	192.168.1.5
10.0.0.54	255.0.0.0	100	10.0.0.100
10.5.0.54	255.0.0.0	254	10.0.0.254

Note: If the IP Network Mask is 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 255.0.0.0, 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 Node	IP Address
20	192.168.1.5
25	10.1.0.240

Messages for FINS node 20 would be sent to 192.168.1.5, and messages for FINS node 25 would be sent to 10.1.0.240.

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.
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 exchange FINS node addresses with the PLC. This sets up the entry in the lookup table for the TCP/IP link. Once the connection is set up the client program can exchange FINS messages with the PLC.

Further Information

Omron CS/CJ Ethernet Connection Guide

For information about configuring CS/CJ PLC Devices with Ethernet communications.

Omron Driver

For information about the Omron Driver.

Glossary

For the meaning of terms used in Fernhill SCADA.