By default, the destination of the Output Data is the Indirect Data Map. Messages sent over Explicit connections are directed to the target object by the Message Router object. An instance of the Connection object is generated for every connection. The Output Data size must be the number of registers you wish to write, plus the Sync Register, if used. The Message Router object is an object which routes explicit request messages from object to object in a device.
The steps required for this are tool-specific. Refer to the topic for details. Ethernet Based Application Layer Protocol for Industrial Automation by John Rinaldi The 6. The destination of the Output Data can be changed to something other than the Indirect Data Map registers, as described below. A second challenge is proper network configuration.
The Identify object is a required object and there is usually only a single instance. These objects are included by the vendor as additional features of the device. An Output Assembly instance organizes the data that is transferred from external devices. An Explicit Message Only device has no Assembly instances. Traditionally, Ethernet had only limited acceptance in Industrial Automation. This standard organizes networked devices as a collection of objects. Two of the most important challenges to the first time user include training and network configuration.
While true in the past, recent developments in intelligent switches have largely eliminated this argument. These super objects contain attributes of one or more Application Layer Objects. The identity object contains related identity data values called attributes. That instance identifies the connection as Explicit or Implicit, sets the packet rate on Implicit connections and holds other descriptive information on the connection. For example, one temperature assembly may be configured to report every time it changes state while the second may be configured to report every one-second regardless of a change in state.
A large number of profiles for many device types have been defined. For example, a vendor of a Temperature Controller with multiple temperature loops may define assemblies for each of the temperature loops and an assembly with data from both temperature loops. These application layer objects are predefined for a large number of common device types. This connection type is also called an Exclusive Owner connection or the controlling connection. These objects are specific to the device type and function. In these cases, additional connection configuration information usually must be entered into a generic device template.
By default, the source of the Input Data is the Indirect Data Map, beginning with Indirect Data Map item 0. For details on the Sync Register, see the topic. It allows users to share files, access printers, send email, search the Internet and perform all the other communications used in the office environment. Instead of letting a user wait while a task is being performed, factory floor data communications needs are real-time or very close to real time. These connection types are generally not used. Careful identification of all your control loops, choosing the correct routers, switches and paths and documenting your network properly are requisites for a communications network which meets your production goals and requires little ongoing maintenance.
These switches create separate collision domains that offer the determinism required of almost all but the most demanding of automation applications. Detractors of Ethernet applications on the factory floor often cite the lack of inherent determinism in Ethernet communications to keep it out of automation applications. An Input Assembly instance organizes the data that is transferred to external devices. Instances of an Assembly object organize the data that is exchanged with external devices. See the topic for details. The Identity object is an example of a required object. A Network object contains the physical connection data for the object.
This should be set to the number of registers you have set up in the Indirect Data Map, plus the Sync Register, if used. Unfortunately which fields are required and how they are presented varies significantly from one tool to the next. This connection type is the least-frequently used. A device vendor can also group Application Layer Objects into assembly objects. This suite of protocols works well for the office environment. Only the lack of a widely accepted, flexible application layer targeted to Industrial Automation has prevented its complete acceptance.
The needs of the factory floor are much different with some very special requirements. It defines the access, object behavior and extensions which allow widely disparate devices to be accessed using a common mechanism. The user can than pick the assembly that is most suited for the application and how often to access each assembly. These objects include the Identity object, a Message Router object and a Network object. The series of application objects for a particular device type is known as the device profile. Note: David Letterman has his Top Ten. Unfortunately space prevents a detailed review of each of these products.