Chapter IV: THE DISPLAY

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Grid

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Electric can display a grid in the editing window, and it can force objects to snap to grid locations. The Toggle Grid command of the Windows menu turns the grid display on and off. The grid spacing defaults to 1 lambda unit. The term lambda indicates a generic spacing unit that can be scaled independently of the actual layout. For example, in the MOSIS CMOS Submicron technology, the value of lambda is 0.2 microns, as shown in the status area under the heading "LAMBDA". When the grid is displayed, the dots are therefore 0.2 microns apart.

Note that the grid is not displayed when it gets to be too dense. Thus, as you zoom out, the grid stops being drawn at some point. However, the fact that the grid should be on is remembered, so it reappears when you zoom back in.

The location of the grid dots is always aligned with the "grab point" of the facet. Since this is normally the lower-left corner, the dots will always pass through that point. If, however, a Facet Center node is placed in the facet (with the Facet Center subcommand of the New Special Object command of the Edit menu) then the grid dots will always pass through that point.

The Grid Settings... command presents a dialog in which spacing and alignment options may be set. It is possible to change the horizontal and vertical grid dot spacings (in lambda units). It is also possible to change how finely the cursor snaps to this grid (when moving or creating circuitry). For example, the grid spacing can be 2x3, but the cursor alignment can be 0.5, indicating that there are up to six different positions for placement inside a displayed grid square.
Figure 4.3

A special grid setting is the alignment of edges, which initially is set to zero (no alignment). This alignment affects the edges of nodes and arcs (as opposed to their lower-left corner, where the grab-point resides). For example, if a 3 lambda wide wire is drawn into a 4x4 contact, the default will be to center that wire, which will place the edges of the wire on half-lambda grid locations. If, however, the edge alignment is set to 1 lambda, then that wire will be forced to one side of the contact so that its edges align. Note that it is not always possible to align edges properly, so you should always check your geometry if you insist on this feature.

Another aid to precise alignment is the Show Cursor Coordinates command of the Info menu. This command causes the X and Y cursor positions to be continuously displayed in the status area. This information appears where the Technology and Lambda used to be. To restore display of Technology and Lambda values, uncheck this menu entry.


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