Working with Cells That Will Be Saved to DWG Files
When you save a DGN file to DWG format, you can use existing cell libraries to help develop the design. Generally, you should use shared cells, as normal cells are not supported in the DWG file format. If your DGN model contains normal cells, however, they will be converted to shared cells in the DWG file.
Annotating Cells: Using Enter Data Fields and Tags
During the conversion to DWG format, cells migrate with no problems, unless they contain enter data fields. AutoCAD does not have an equivalent feature. To annotate cells in DGN files that will be saved to DWG file, use tags rather than enter data fields.
Using Enter Data Fields in Cells
For drawing annotation, MicroStation PowerDraft users have traditionally embedded enter data fields in cell symbols. For example, items like valve designators and door symbols have often been created using this type of cell annotation.
When you save the DGN file as a DWG file, the enter data fields that are not used in cells are converted to text. However, the enter data fields in cells are handled somewhat differently.
In a DGN file, an enter data field may be used to annotate a normal cell (enter data fields cannot be used with shared cells). During conversion, the product converts an enter data field that is part of a cell to an AutoCAD attribute linked to a block. In AutoCAD, the enter data field's value appears as an attribute positioned precisely where the enter data field was located in the MicroStation PowerDraft cell.
Like MicroStation PowerDraft tags, all AutoCAD attributes have an associated label or name. Since MicroStation PowerDraft enter data fields are not defined with a label, the Save As process automatically generates a label for each enter data field that is converted to an attribute. The new label is the cell name plus a sequence number.
These automatically-generated attribute labels may be undesirable, particularly if DWG specifications require specific attribute usage and labels. Since MicroStation PowerDraft cannot store labels for enter data fields, you should not use enter data fields in situations where specific labels are required. Instead, incorporate tags into the cell definition, as these become block attributes when the DGN file is converted to DWG.
Understanding Insert Layer Control for Normal Cells
The insert layer for a normal (unshared) cell saved in the DWG file corresponds by default to the level of the cell's first component element.
In certain cases it may be desirable to override the default insert layer. Consider, for example, what can happen when levels within a viewport (model attached to sheet) are turned off and Level Display is set to View Display. In this case, unless an override is specified, if an insert exists on a layer that is frozen it will not be displayed at all even if the component layers are displayed.
To override the default insert layer for normal cells, set the desired layer name in the Save As DWG/DXF Options dialog’s Insert Layer for Normal Cells field.
When exporting parametric cells to a DWG file, the parametric cells are first dropped to shared cells, which are then exported to DWG.
The following topics provide more details about working with cells: