Electric VLSI Design System User's Manual

Chapter 2: Basic Editing

2-3: Circuit Deletion

To remove circuitry, select nodes and/or arcs and use the Selected command (in menu Edit / Erase). A keyboard shortcut for this is the Delete key. If there is a highlighted area rather than a highlighted object, everything in the area is erased.

Note that an arc always connects two nodes, and therefore it cannot remain if one of the nodes is gone. This means that certain rules apply to circuit deletion:

When a node is erased, all connecting arcs are also deleted. However, if a node is deleted that has exactly two arcs, connected as though the node were in the middle of a single arc, then the node and two arcs are replaced with a single arc.
In the interest of cleanliness, if an arc is erased, any isolated pins are also erased.

If an erased node has an export on it (as in this example), then the export disappears and so do all arcs connected to the port on instances of the current cell (for more information on hierarchy, see Chapter 3).

The exception to these rules is the Nodes Preference "Reconstruct arcs and exports when deleting instances" (see Section 6-2) which requests that when a cell instance is deleted, and it has arcs connected to it or exports from it, these arcs and exports will be "reconstructed" so that they continue to exist. Reconstruction consists of creating pins where the cell instance ports used to be so that the arcs and exports can continue to exist.

Figure 3.14 When an area is selected instead of objects (see Section 4-7-2) the Edit / Erase / Selected command erases all geometry in the highlighted area. All arcs that cross into that area will be truncated. Thus, this command erases precise geometry, independent of the structure of nodes and arcs. Note that the area to be erased is adjusted by the current alignment values (see Section 4-7-2).

Two special arc deletion commands are Arcs Connected to Selected Nodes and Arcs Connected Between Selected Nodes (in menu Edit / Erase). The first command removes all arcs that have either end on a selected node. The second command removes all arcs that have both ends on selected nodes.

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