Chapter 3: HIERARCHY


3-4: Examining Instances


When instances are initially created, they are drawn as black boxes with nothing inside. This form of instance display is called unexpanded, as opposed to expanded display which shows the actual layout inside the instance. To expand an instance, select it and use the subcommands of the Expand Cell Instances command of the Cells menu. The One Level Down subcommand opens up the next closed level; the All the Way subcommand opens up all levels to the bottom; and the Specified Amount... lets you type a number of levels of hierarchy to expand. These commands expand all highlighted cells. If a highlighted cell is already expanded, this command expands any subcells inside of the instance, repeatedly down the hierarchy.

Once expanded, a cell instance will continue to be drawn with its contents shown until the subcommands of the Unexpand Cell Instances command are used. These commands return cell instances to their black-box form, starting with the deepest subcells that are expanded at the bottom of the hierarchy. The One Level Up subcommand closes up the bottommost expanded level; the All the Way subcommand closes all levels from the bottom; and the Specified Amount... lets you type a number of levels of hierarchy to close.

The expansion information can also be set or reset by using the Get Info command of the Info menu and clicking on the "Expanded" or "Unexpanded" buttons.

There are times when you want to see the layout inside of a cell instance, but only temporarily. The Look Inside Highlighted command of the Cells menu displays everything in the highlighted area, down through all hierarchical levels. This is a one-shot display that reverts to unexpanded form if the window is shifted, scaled, or redrawn.

There is a slight difference in specification between the Expand Cell Instances subcommands and the Look Inside Highlighted command. The Expand Cell Instances subcommands affect cell instances only, and thus any instances that are highlighted or in the highlighted area will be completely expanded. The Look Inside Highlighted command affects layout display in an area, so only those parts of instances that are inside of the highlighted area will be shown. Thus, the command Look Inside Highlighted is more precise in what it expands and can be used, in conjunction with the rectangle select button, to show only a specific part of the circuit.

Examining cell instances can be quite time consuming, especially if you are looking at an entire chip, fully flattened. To avoid delays, Electric simplifies the display of cells when the scale grows too tiny. These tiny cells get "hashed-out" rather than fully drawn. See Section 3-7 for more information.

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