6.8 DCS Channel Assignment

During the channel assignment the relationship between a channel provided by the DTM and a channel within the Frame Application (DCS channel) is established by the Frame Application. To do this, the Frame Application has to get the channel properties from the DTM. To get this information it asks the DTM for the channels of the current instance and iterates over the received channels.

For the assigned channels the Frame Application sets the read-only-flag within the channel parameters. This flag causes that the channel is not deleted until the channel assignment is released.

If a DTM instance represents a complete device, all information for channel assignment is available at this DTM.

In case of a modular device like remote I/Os which is represented by one DTM, the internal structure is also available via the parameter interface. From the channel assignment point of view this information allows the Frame Application to generate a structured presentation, so that there is no difference for a user whether he works with a single DTM or with several DTMs which represent the parts of the modular device.

Used methods:
IFdtContainer::LockDataSet()
IFdtContainer::UnlockDataSet()
IDtmParameter::GetParameters()
IDtmChannel::GetChannels()
IFdtChannel::GetChannelParameters()
IFdtChannel::SetChannelParameters()

The following figure shows a sub structure with DTMs for modular devices especially for remote I/Os with modules of different vendor. The connection of the Device-DTM and its module DTMs is established via the standard topology methods. At this sub structure the Device-DTM is the gateway between the fieldbus and the proprietary backplane bus. So the communication can be realized by the mechanisms of nested communication.

In this case ‘LinkedDevice’ specifies the connection between a communication channel of the bus coupler (DTM Device) and the modules (DTM Module) as well as the connection between a communication channel of a module and a connected device. Especially for a remote I/O the FdtChannels are similar to the slots at the backplane.

So if a DTM instance represents only a part of a device, the information for channel assignment has to be collected by the Frame Application In case of a modular device like remote I/Os, the gateway is signed as main DTM and is the start point to collect the information of the sub DTMs which at least belong to the same device. So the internal structure is represented by the topology. From the channel assignment point of view the channel information together with the topology allows the Frame Application to generate a structured presentation, so that there is no difference for a user whether he works with a single DTM or with several DTMs which represent the parts of the modular device.

Used methods:
IFdtContainer::LockDataSet()
IFdtContainer::UnlockDataSet()
IDtmParameter::GetParameters()
IDtmChannel::GetChannels()
IFdtChannel::GetChannelParameters()
IFdtChannel::SetChannelParameters()
IFdtTopology::GetChildNodes()