Saturday, April 2, 2011

Overview of the MAP Communication Environment Using PLC5

This article will introduce you to MAP communication using PLC5 and give you information how it relates to your OSI coprocessor. It covers about:
• OSI (Open Systems Interconnect)
• MAP (Manufacturing Automation Protocol)
• MMS (Manufacturing Message Specification)
• Modeling Concept of the MMS
• MAP communications and your OSI coprocessor

It consists general subject overview and are not meant to give depth information. The Open Systems Interconnect (OSI) is a standard that provides the framework to define the process of communication between nodes (i.e., terminals, PLC Controllers, computers). There are a lot of work that need to be done when the 2 point contact by each other point via the network. The OSI standard defines these activities in its seven–layer reference model.

The seven layers define the activities involved in communicating on the network and services required to perform those activities. The specifications of each layer dictate how the functions are accomplished. The protocols carry out the tasks within layers. Protocols are define as the rules for how information is created and transferred between two nodes. The protocols are actually the component that is applied, the OSI model serves as a reference to study the different communication aspects between equipments.

The system of OSI enable for many different manufacturers’ devices on the same network to communicate with each other. In other words, as long as two different manufacturers build protocols that fit in the seven layer model the same way, those two devices will be able to communicate. Each node on an OSI network is equipped with a layer mechanism that organizes the standard of OSI rules. Individual layer is capable to communicate with just its component within the point of sending or receiving the data.

Manufacturing Automation Protocol (MAP) is a protocol set based on the model of OSI seven–layer. MAP specifies a set of protocols that have to accomplish certain works within each of the model’s seven layers. OSI coprocessor is applicable the MAP 3.0 Protocol. The reference models of seventh and first layers are the two layers that are most distinct to application. The seventh layer is the Application layer, with OSI coprocessor first interacts with your application program. The first layer is the Physical layer, with OSI coprocessor connects to the network media. OSI coprocessor connects to MAP 802.4 network media. The Application Layer for the MAP 3.0 Specification consist a unique set of services called MMS (Manufacturing Message Specification).

Manufacturing Message Specification (MMS) gives services visible directly to the user. MMS specifies a method to communicate with intelligent plant–floor devices. MMS is not a program application, it provides services to application programs. These programs use the services to communicate with equipments on the network. MMS gives MAP network equipments a services set that they can all access, allowing them to communicate freely. The following sections provide a brief overview of MMS. For detailed information, refer to the ISO/IEC 9506 Part 1 (MMS –– Service Definition).

The MMS dominant aspect is the concept of modeling. MMS defines models that describe the way in which resources are made available and the way in which these resources are accessed. At the center of the MMS modeling concept are the VMD (Virtual Manufacturing Device) abstract object models.

The VMD describes the visible behavior externally of an MMS device when it makes resources (i.e., data table memory, program files) available to other MMS equipments. Assume, for instance, that an MMS device exists and it makes system data table memory available to other MMS equipments. It is the VMD that explains the way in which that MMS equipment makes the data table memory available.

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