Walking Through the Design

This procedure explains how to select successive logic by connectivity rather than by name. This process helps you see which floorplanned logic elements drive other logic in the design.

Finding Logic

1. Determine the logic that is of interest.
   
   
2. Select Edit Find.
   
   This command opens the Find dialog box.
   
   
3. In the Connections list box, select either Loading Selected Logic or Driving Selected Logic.
   
   
4. Click Find.
   
   
5. Click Select Found.
   
   

The Floorplanner searches the design for the appropriate symbols. The Floorplanner highlights the first “found” symbol in the Design Hierarchy window with an arrowhead at the left of the symbol line text. Matching symbols in the Floorplan window flash (blink) if you have enabled Flashing.

Finding Nets

1. Determine the nets that you want to find.
   
   
2. Select Edit Find.
   
   This command opens the Find dialog box.
   
   
3. In the Type list box, select Nets.
   
   
4. Use the Name dialog box, or Connections list box to find the desired net(s).
   
   
5. Click Find.
   
   
6. Click Select Found.
   
   

For logic that is placed in the Floorplan or Placement windows, the Floorplanner searches the design and highlights the appropriate nets by drawing them as red lines. Note that only currently selected nets appear in red; previously found nets, which were deselected, are drawn with black lines.

Displaying the Ratsnest

The Floorplanner shows connectivity between logic symbols in the Floorplan window with the aid of the ratsnest display. A ratsnest is a display of lines between logic blocks that indicate connections between the inputs and the outputs of floorplanned logic.

By default, the Floorplanner automatically displays ratsnest for selected floorplanned logic and selected nets. Whenever you place selected logic in the Floorplan window, the ratsnest displays the connectivity between the logic symbols.

Using the Ratsnest

By default, the ratsnest is on. As you place selected logic in the Floorplan window, the ratsnest lines show connectivity. You can see which logic is connected to a given net by selecting nets in the Ratsnest dialog box and choosing the appropriate connection.

1. Select some floorplanned logic. Use the mouse to draw an area around the desired logic or click on an individual piece of logic.
   
   The Floorplanner draws the ratsnest to the associated logic.
   
   
2. In the Design Nets window, use the right mouse button to click List Visible Nets. The names of the nets connected to the selected logic appear in the window.
   
   
3. Select a net in the Design Nets window and look at the Floorplan window.
   
   

The Floorplanner draws a ratsnest of the selected net in red.

Viewing Selected Nets in the Ratsnest

Use the Design Nets window to display specific nets in the Floorplan window. Click on a net in the Design Nets window. The Floorplanner window displays the net in red lines. To display consecutive nets in the Design Nets window, hold down the Shift key while selecting the desired nets. To display non-consecutive nets, hold down the Control key while making your selections.