I’m often asked what is EtherNet/IP or can you give me an EtherNet/IP Quick Introduction? So here’s the top 6.5 things you need to know about EtherNet/IP. (Note: David Letterman has his Top Ten. I’m only 65% as good as David Letterman)
1) EtherNet/IP is an application layer protocol that is transferred inside a TCP/IP Packet. That means that EtherNet/IP is simply the way data is organized in a TCP or UDP packet.
2) All devices on an EtherNet/IP network present their data to the network as a series of data values called attributes grouped with other similar data values into sets of attributes called Objects.
3) There are EtherNet/IP Required Objects – Identity, TCP, and Router that every device must have. The EtherNet/IP Specification defines those objects.
4) There are EtherNet/IP Application Objects that have the data for your specific device. For example, an EtherNet/IP Drive device has a Motor Object. EtherNet/IP devices that support specific devices all have the same set of EtherNet/IP application objects.
5) There are two kinds of messages that are transferred between an EtherNet/IP Scanner Device (opens connections and initiates data transfers) and EtherNet/IP Adapter devices (provides data to Scanners). These messages are Explicit Messages (asynchronous, as needed) and I/O Messages (Data messages that are continuously transferred).
6) EtherNet/IP is part of CIP, the Common Industrial Protocol. CIP defines the Object structure and specifies the message transfer. CIP protocol over CAN is DeviceNet. CIP protocol over Ethernet is EtherNet/IP.
6.5) Our company, RTA, is the leading supplier of EtherNet/IP technology. RTA can supply Royalty Free EtherNet/IP Source Code Software stacks, EtherNet/IP PCBs, and Modules.
Ethernet/IP uses the tools and technologies of traditional Ethernet. Ethernet/IP uses all the transport and control protocols used in traditional Ethernet including the Transport Control Protocol (TCP), the Internet Protocol (IP) and the media access and signaling technologies found in off-the-shelf Ethernet interface cards. Building on these standard PC technologies means that EIP works transparently with all the standard off-the-shelf Ethernet devices found in today's marketplace.
Ethernet/IP is a certifiable standard. The groups supporting EIP plan to ensure a comprehensive, consistent standard by careful, multi-vendor attention to the specification and through certified test labs as has been done with DeviceNet and ControlNet.
AN OVERVIEW OF CIP
The Common Industrial Protocol (CIP) is a communications protocol for transferring automation data between two devices. In the CIP Protocol, every network device represents itself as a series of objects. Each object is simply a grouping of the related data values in a device. For example, every CIP device is required to make an Identity object available to the network. The identity object contains related identity data values called attributes. Attributes for the identity object include the vendor ID, date of manufacture, device serial number and other identity data. CIP does not specify at all how this object data is implemented, only what data values or attributes must be supported and that these attributes must be available to other CIP devices.
The Identity object is an example of a required object. There are three types of objects defined by the CIP protocol:
1. REQUIRED OBJECTS
Required objects are required by the specification to be included in every CIP device. These objects include the Identity object, a Message Router object and a Network object.
A. The identity object contains related identity data values called attributes. Attributes for the identity object include the vendor ID, date of manufacturer, device serial number and other identity data.
B. The Message Router object is an object which routes explicit request messages from object to object in a device.
C. A Network object contains the physical connection data for the object. For a CIP device on DeviceNet the network object contains the MacID and other data describing the interface to the CAN network. For EIP devices, the network object contains the IP address and other data describing the interface to the Ethernet port on the device.
2. APPLICATION OBJECTS
Application objects are the objects that define the data encapsulated by the device. These objects are specific to the device type and function. For example, a Motor object on a Drive System has attributes describing the frequency, current rating and motor size. An Analog Input object on an I/O device has attributes that define the type, resolution and current value for the analog input.
3. VENDOR SPECIFIC OBJECTS
Objects not found in the profile for a device class are termed Vendor Specific. These objects are included by the vendor as additional features of the device. The CIP protocol provides access to these vendor extension objects in exactly the same method as either application or required objects. This data is strictly of the vendors choosing and is organized in whatever method makes sense to the device vendor. In addition to specifying how device data is represented to the network, the CIP protocol specifies a number of different ways in which that data can be accessed such as cyclic, polled and change-of-state.
ADVANTAGES TO EIP
The advantages of the CIP protocol layer over EIP are numerous. The consistent device access means that a single configuration tool can configure CIP devices on different networks from a single access point without using vendor specific software. The classification of all devices as objects decreases the training and startup required when new devices are brought online. EIP provides improved response time and greater data throughput than DeviceNet and ControlNet. EIP links devices from the sensor bus level to the control level to the enterprise level with a consistent application layer interface.
There are numerous application layer competitors to EIP including Modbus/TCP from Groupe Schneider, ProfiNet from Siemens, HSE Fieldbus from the Fieldbus foundation and other vendors. Unfortunately space prevents a detailed review of each of these products. However, none of these competitors can provide the vendor support, flexibility and total architecture support offered by the implementation of CIP over Ethernet.