Electric VLSI Design System User's Manual

Chapter 3: Hierarchy

3-5: Moving Up and Down the Hierarchy

Each editing window in Electric displays a single cell. Editing changes can be made only to that cell, and not to any subcells that appear as instances. Thus, you may be able to see the contents of a cell instance, but you cannot edit it.

To edit a cell instance, use one of these commands in the Cell / Down Hierarchy menu:

Down Hierarchy descends into the definition of the currently selected cell instance. You will now be able to edit that cell.
Down Hierarchy, Keep Focus descends while keeping the same window zoom and pan.
Down Hierarchy, New Window creates a new window in which to show the lower-level cell.
Down Hierarchy, Keep Focus, New Window creates a new window in which to show the lower-level cell, while maintaining the zoom and pan factor.

The opposite of going down the hierarchy is the Up Hierarchy command (in menu Cell / Up Hierarchy), which pops you to the next higher cell in the hierarchy. If there was an associated Down Hierarchy command, then this returns you to the place where you started, up the hierarchy. If the Down Hierarchy commands were not used, Electric attempts to figure out the next higher cell in the hierarchy, switching icons for schematics where appropriate. If there are multiple possibilities (because the current cell is used in many locations) then you will be prompted for a specific location. An alternate version of this command is Up Hierarchy, Keep Focus which moves up the hierarchy, but keeps the current cell's zoom and pan factors the same so that the circuitry does not move on the screen.

Besides traversing the hierarchy, you can also traverse the sequence of cells that has been edited. To edit the cell that was previously displayed, use the Go Back a Cell command (in the Cell / Cell Viewing History menu) and to go forward in the list, use the Go Forward a Cell.
Figure 3.22 These commands are also accessible from the tool bar "back" and "forward" buttons. If you right-click on these buttons, you are given a list of cells and can jump directly to one of them.

When going down or up the hierarchy, if an export or port is selected, then the equivalent port or export is shown after the level of hierarchy has changed.

Layout Considerations

If a layout cell is selected, you can use the Down Hierarchy In Place command to edit the cell while showing the upper level of the hierarchy. A red border is drawn around the cell now being edited and the surrounding geometry at the upper level, which is not editable, is grayed-out. To change the border color, use the Layers Preferences (in menu File / Preferences..., "Display" section, "Layers" tab) and set the colors for the layer "SPECIAL: DOWN-IN-PLACE BORDER". To disable the graying-out of upper levels of hierarchy, use the Display Control Preferences and uncheck "Dim upper levels of hierarchy when editing Down-In-Place".

The Down Hierarchy In Place To Object command finds the object under the cursor (at any level of the hierarchy) and descends to that level. This may go down the hierarchy many levels. It descends "in place" so that the original geometry is visible, but higher-levels are grayed-out. It is useful when trying to quickly find the hierarchy that exists at that point, and see which instances were used to construct it. Note that there may be many different levels of hierarchy under the cursor, which will cause a popup to appear listing the possible subcells to edit.

Schematic Considerations

If an icon is selected, the Down Hierarchy commands will take you to the associated schematic. If the icon that is selected is already in its own schematic (you can place an icon inside its own schematic for documentation purposes), then the Down Hierarchy command takes you to the actual icon so that you can edit it. The Down Hierarchy In Place command takes you directly to the icon, showing it in the context of the upper-level schematic.

Schematic nodes can be arrayed by giving them array names (see Section 6-9-3). When you descend into an arrayed node, the system does not know which element of the array you are entering. Most of the time, the specific element is irrelevant, but if the circuit is being simulated, the specific instance may be necessary for cross-probing. Therefore, if the cell is being simulated and you descend into an arrayed node, you will be prompted for the specific element that you wish to visit.

There are other situations that cannot be detected, where the specific element needs to be known. To solve this problem, you can request that Electric prompt for the specific element in all situations where an arrayed node is visited. To do this, check "Always prompt for index when descending into array nodes" in the Nodes Preferences (in menu File / Preferences..., "General" section, "Nodes" tab)

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