7-9: The Generic Technology
The Universal arc in the Generic technology is able to make a connection between any two components, even if they are in different technologies. This is useful when mixing technologies while still maintaining proper connectivity, for example when simulating. The Invisible arc attaches any two components, but makes no electrical connection. It is useful for constraining otherwise unrelated components. The Unrouted arc makes arbitrary electrical connections, like the universal arc, but routers know to replace them with real geometry. None of these arcs produce any actual geometry in IC descriptions, but they make important conceptual connections.
Any existing arc in a normal technology can be converted to one of these three special arcs by using the Change... command of the Edit menu. Also, the unrouted arc can be selected for subsequent wiring with the Get Unrouted Wire subcommand of the Routing command of the Tools menu.
There are also special nodes in the Generic technology. The Universal-Pin is a node that can connect to any arc. This is useful as an intermediate component when replacing (first you replace the unwanted node with a Universal-Pin to allow it to fit with the existing arcs; then you replace the arcs; finally you put the desired new node in place).
The Invisible-Pin is used for holding text, and it does not appear in hardcopy output (this is what is created when you use the Text (nonlayout) subcommand of the New Special Object command of the Edit menu). This pin can also connect to any arc.
A special primitive, called Facet-Center, defines the origin of any cell. It is also available from the Cell Center subcommand of the New Special Object command of the Edit menu. Once the node is placed, instances of the current cell use this node's location, rather than the lower-left corner, as the grab point for cursor-based references. For example, if you place this node in the upper-right corner of a cell, then creation commands place instances such that their upper-right corner is at the cursor. Deleting this node restores the lower-left corner as the grab point. See Section 3-3 for more information on cell centers.
A special primitive, called Essential-Bounds, defines an alternate boundary of any cell. At least two of them must be placed in opposite corners, although 4 can be place to make it look better. This primitive is also available from the Essential Bounds marker subcommand of the New Special Object command of the Edit menu.
Note that the Cell-Center and Essential-Bounds nodes are made "hard-to-select" by default, which means that they can be selected only by using the special select button. Use the Get Info command of the Info menu, and check "Easy to Select", to allow simple selection of these components.
A special primitive, called Simulation-Probe is recognized by simulators and visually modified to reflect whatever it is connected to. The simulators that reflect the state of the circuit by drawing lines along arcs also fills-in these probe nodes. It provides a visual display of simulation activity, and works especially well when the VCR controls in the waveform window are used.
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