Access to P-NET from PC’s

PC’s are often used in P-NET installations as one of the masters. PC’s are normally connected to P-NET by means of plug in cards.

A product called VIGO has been developed for P-NET.
VIGO is a PC based Fieldbus Management System. It enables a physical plant to be described in terms of data, related data structures and where data is located.

VIGO is also a communication system that manages data security and integrity for data enquiries made within the plant.

VIGO keeps track of the relationship between the physical objects within the plant, and the associated Fieldbus nodes. It also includes the set of files describing the related control programs, configuration and calibration parameters, as well as tools for configuration, backup, download etc.

The routing and handling of several simultaneous information packages for the same, or different networks, are also managed by VIGO, via a real-time communication kernel. When several applications try to access the same bus system, problems will occur in a Windows multi-task environment. This is solved by VIGO, which ensures that communication packages and messages do not get mixed.

A facility available to enable the fast real-time exchange of data between MS-Windows applications is called “OLE2 Automation” (Object Linking and Embedding).

VIGO is an OLE2 Automation Server, which creates a consistent and transparent interface from the user program (application), to the physical elements (objects) within the plant.
In this way, VIGO provides a simple interface to standard program packages such as Visual Basic and Visual C++, spreadsheets, databases, Man-Machine interfaces and other visualisation programs such as SCADA.

Below is shown a Visual Basic program example (EXCEL macro language), using three easy steps:

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Step 1: set AA = Createobject(“VIGO”)

VIGO creates a virtual object: AA, which then becomes part of the Visual Basic programming environment

Step 2: AA.PhysId = “Setpoint”

The virtual object AA is made to point to the physical object, by assigning the physicalidentifier to a property called PhysId.

Step 3: X = AA.ExFloat (Get Setpoint) or AA.ExFloat = 37,0 (Set Setpoint)

All manipulation of the physical object is performed via the virtual object. See fig. 7.

To operate on the object, a type property must be appended to indicate the type of variable in the node. Exfloat indicates that the object variable is of a real type (floating point), Exbool would indicate a boolean type, etc.

The object can be used in normal assignments, such as set or get functions. Many objects can be created for several independent applications.

VIGO is a collection of several program elements. It is an open system as regards allowing the addition of elements for networks from other vendors. All these elements are handled by and integrated into VIGO, leading to a very simple and well defined interface to any Fieldbus data. The elements of VIGO are shown in fig. 8.

Application: An independent user application program, which communicates via VIGO.

VIGOSERV: An OLE2 Automation server that provides the interface between VIGO and the applications.

IDC: An Instruction/Data Converter, which converts a VIGO service into a specific network instruction, and sets up data using the correct syntax suitable for the destination node, and vice versa.

HUGO2: A real-time communication kernel that provides the possibility of executing several Fieldbus communication applications in parallel.Figure 7.The

Manager Information Base: The MIB contains a set of data structures, which describe the physical system. The MIB translates a variable name into a specific node address, variable address, type specification, etc.

The Drivers: These take care of sending and receiving information via a specific network.

Figure 8: The elements of VIGO.