2.1 FDT Overview

This specification describes the FDT Objects and their interfaces implemented by the Frame Application and the device specific applications called Device Type Manager (DTM). DTMs can connect to monolithic Frame Applications or to Frame Applications made of different components provided by one or more vendors. Vice versa a Frame Application can support the integration of device specific DTMs of different vendors.

DTMs act as servers for device information and functionality. Different vendors may provide DTM Servers. Vendor-supplied code determines the device functionality and data to which the Frame Application has access.

At a high level, a DTM is comprised of several objects: the server object and channel objects. This model represents a view on a device from an external application. There is the device itself that contains a certain set of functionality. To access the device’s functionality, data must be exchanged between device and environment via communication channels. These channels may be identical to I/O connections of a Remote-I/O or to different process values measured by a transmitter and communicated via the fieldbus. According to this model, the DTM server object maintains the functionality of the device. The FDT channel objects maintain information about the channels or the I/O data of the device, respectively. Furthermore, the FDT channel objects provide the mechanism for data exchange between DTM and Frame Application.

Within each channel the DTM can define one or more fieldbus specific parameters that give information about the channel like data types, ranges, alarms etc.

Figure 2-2 - Channel/Parameter Relationship

These fieldbus specific parameters contain all information a Frame Application needs for the integration of the I/O data of a device. In general, channels carrying the parameters to describe the I/O data are not the data sources - they are just representations for them. These parameters should be thought of as simply specifying the address of the data, not as the actual source of the data that the address references. Furthermore a channel can carry the functionality for communicating via the channel with a secondary communication protocol. Such a channel is called ‘Gateway Channel’ and will be described in detail at the chapter about ‘Nested Communication’. Detail information about the FDT object model can be fond in chapter 4.2