1.　Ethernet is a specification defining the types of cables used in the local area network (LAN). Ethernet enables data transmission among computers at a communication speed of 10Mbps-100Mbps. Ethernet cable now mostly used in OA (Office Automation) is a 10Mbps twisted pair cable (UTP). Ethernet enables communication using software protocols developed by many multi-vendors.

2.　FL-net (OPCN-2) is a network that connects FA controllers such as programmable controllers (PLC), numerical control units (NC), etc. and enables mutual exchange of control data among controllers at high speed. The same cable as for Ethernet is used.

3.　Ethernet connects controllers with an upper layer computer, a personal computer, etc. and is used for information transmission and control purposes such as production information, performance collection, etc., while FL-net (OPCN-2) connects controllers and enables fast exchange of control data. If one controller implements both Ethernet for an upper layer and FL-net (OPCN-2) for among controllers, do not connect cables incorrectly.

4.　An FL-net (OPCN-2) unit is implemented in an FA controller such as a programmable controller (PLC), a numerical control unit (CNC), etc. and transmits and receives data cyclically among controllers only by assigning a station number (a node number) and common memory (also called link register) for linking in the same manner as the "CPU link unit" of a normal PLC. In this case a particular communication program for PLC, etc. is unnecessary. Moreover, also when reading or writing of memory contents, communication parameters, etc. in PLC is conducted on a personal computer, etc., a particular communication program for PLC, etc. is unnecessary. However, if data transmission and reception using message transmission between controllers are conducted, a communication program is necessary for each individual controller.

5.　A protocol is a rule necessary for regulating communication.Protocols supported by FL-net (OPCN-2) are UDP/IP and "FA link protocol" which is located in the upper layer of UDP/IP.

6.　An FL-net (OPCN-2) unit implemented in an FA controller such as a programmable controller (PLC) and a numerical control unit (NC) is an intelligent unit that has a processor on its board. The Ethernet card of a personal computer is a non-intelligent type card, i.e., what is called a dumb board. Although depending on performance and usage of a personal computer, an intelligent FL-net (OPCN-2) board is generally recommended.

7.　Networking topology means the network wiring configuration. Topology is divided roughly into 3 configurations: star type (tree type), bus type and ring type. In plain language it indicates a logical wiring configuration rather than a physical wiring configuration.10BASE-T, which FL-net (OPCN-2) uses, is star type topology, while 10BASE5 is bus type topology.

8.　Standards for Ethernet cables most generally used and a part of their characteristics and usage limitation are described in the following. Note: the numerical value in brackets indicates where a repeater is used.

9. No. Ethernet (formally complying with IEEE802.3 Standard) is used to build an FL-net (OPCN-2) system. Specific specifications are unnecessary.

10. Different types of Ethernet media are interconnected among Ethernet cables, using repeaters, media converting adapters, etc. These products are sold by many vendors.

11.　General usages are as follows.

12.　Standard IP addresses of FL-net (OPCN-2) are 192.168.250.n.
Network address: 192.168.250
Host number (node number): n = 1 to 254
However, node numbers 250 to 254 are reserved for maintenance tools.

13.　FL-net (OPCN-2) is certified by the certification body where conformity testing and interconnectivity testing are conducted. Certificates are issued for devices that have passed these tests. Devices complying with FL-net (OPCN-2) can be reliably used.