Using the Electric VLSI Design System

Chapter V: WIRE PROPERTIES

| ## 4: Other Arc Properties |

In addition to the constraining properties, there are a set of characteristics that can be placed on arcs. These properties affect the appearance of the arc and cause it to be redrawn in a different style.

### Directionality

For documentation purposes, it is possible to display a directional arrow on arcs that indicates flow. This property can be set or reset with the Directional command of the Arc menu. It may also be controlled by checking the appropriate box in the Get Info command of the Info menu.

The arrow always runs from the tail of the arc to the head of the arc unless you reverse the arc (with the Reverse command of the Arc menu or by checking the "Reverse head and tail" box in the Get Info dialog).

### Negation

Arcs in the Schematic technology may be negated, which causes them to have a bubble drawn where they attach to schematic elements. This property can be set or reset with the Negated command of the Arc menu. It may also be controlled by checking the appropriate box in the Get Info dialog.

Although Electric attempts to place the bubble on the correct end of the arc, it can be reversed with the Reverse command of the Arc menu or by checking the appropriate box in the Get Info dialog. Since there can be only one negating bubble on an arc, users who want two must use two arcs, connected by a pin. Negated arcs make no sense in layout technologies and are ignored.

### End Extension

All arcs are drawn so that their geometry extends beyond their endpoints by one-half of their width. This can be disabled by unchecking the "Ends extend" box in the Get Info dialog.

Individual ends of an arc may be controlled by checking the "Ignore head" and "Ignore tail" boxes in the Get Info dialog. When an end has been ignored, the property associated with it does not occur. This means that directional arcs have their arrowhead omitted (when the head is ignored); negated arcs do not have the bubble drawn (when the tail is ignored); and arcs with their ends not extended have that end extended.

### Naming

Another property of an arc is its name. This is a string that is displayed on the arc and used to name the electrical network connected to that arc. The "Name" field in the Get Info dialog allows you to specify this property, which is then displayed on the arc. Note that exported ports are another way of naming a network.

### Curvature

The final arc properties to be mentioned are used only in circular geometry. Although most arcs cannot handle curvature, those in the Artwork and Round CMOS ("rcmos") technologies can. The Curve through Cursor command of the Arc menu requests that the curvature of the currently highlighted arc pass through the location of the cursor. The Curve about Cursor command requests that the currently highlighted arc curve between its endpoints such that the center of curvature is at the location of the cursor. Click at the appropriate point after issuing these commands. In the latter command, two curvatures are possible (clockwise and counterclockwise), so use the "Reverse head and tail" checkbox in the Get Info dialog to make a distinction. The Remove Curvature command makes the arc straight.

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