2.4.1 The Device Type Manager (DTM)

There are different types of fieldbus devices installed on a plant. Therefore, you need one or several DeviceTypeManagers (DTMs) to handle these different devices. Fieldbus device manufacturers deliver the DeviceTypeManagers. They are installed in the system, so that the system can be dynamically extended by installing new DTMs for new fieldbus devices.

It depends on the software design of the DTMs, whether they are responsible for one device type or a group of device types. It is possible to implement even one very powerful DTM for a group of targeted device types.

Usually, one DTM handles one device type and knows everything about its specific parameters, behavior, and limitations.

Figure 2-4 - The DTM Interfaces

The interfaces IDtm and IDtmInformation have to be implemented by each DTM. These interfaces provide the base functions and information for controlling a DTM. From a Frame Application’s point of view, all task-related interfaces for the interaction with the device functionality are available via these interfaces. Which task related interfaces are provided depends on the capability of the DTM and the according device. Each interface will be described in detail at its own chapter.

In order to represent the device’s I/O connections or process values accessible for data exchange with the Frame Application, the DTM can implement an FDT-Channel object (Process Channel). This object implements at least the IFdtChannel interface that gives access to all parameters of the channel which describes the channel itself.

If the device provides communication functionality, like a fieldbus adapter or a gateway, the FDT-Channel object must implement further interfaces for the communication via this channel (Communication Channel). Each interface of the FDT-Channel object will be described in detail at its own chapter.