Chapter 1: Introduction
1-10: IC Layout Tutorial
1-10-5: IC Layout Tutorial: Constraints

Once components are wired, moving them will also move their connecting wires. Notice that the wires stretch and move to maintain the connections. What actually happens is that the programmable constraint system follows instructions stored on the wires, and reacts to node changes. The default wire is fixed-angle and slidable, so the letters "FS" are shown when the wire is highlighted.

Figure 1.29

Select a wire and issue the Rigid command (in menu Edit / Arc). The letters change to "R" on the arc and the wire no longer stretches when nodes move. Find another arc and issue the Not Fixed-angle command. Now observe the effects of an unconstrained arc as its neighboring nodes move. These arc constraints can be reversed with the Rigid and Fixed-angle commands. See Section 5-2-1 for more on these constraints.

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