Chapter VI: ADVANCED EDITING

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Networks

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A collection of electrically connected components defines a network. Networks may span many arcs, or they may reside on only a single port of a single node. Since networks are stored in the Electric database, they can be immediately accessed when needed.

When any part of a network is selected, the Show Network subcommand of the Network command of the Tools menu will highlight all arcs on that network. A list of the named nets in the current facet is available with the List Networks command of the Info menu.

Network names are derived from exported ports and named arcs in a facet. The name given to an exported port becomes the network name of all arcs connected to that port. Similarly, the name given explicitly to an arc (by setting the name field in the Get Info command) becomes the name of the network for all connected arcs. Network names can be renamed with the Rename Object command of the Info menu.

Two phenomena can occur in this network naming scheme: a network can be multiply named, and it can span disjoint circuitry. In the former case, two connected arcs or ports may be given different names. This causes the same network to have multiple names, which are listed together. For example, if you export a port on a contact node and call that port "clock", then you select an arc connected to that contact node and name it "sig", this circuitry will be on the network "clock/sig."

The other phenomenon of network naming is when two unconnected arcs are given the same name. This causes the two arcs to be implicitly joined into one network for schematics. To cause this same effect in IC layout technologies, use the Unify All Like-Named Nets subcommand of the Network command of the Tools menu.

A final aspect of network naming is bus names. In the Schematic technology, the bus arcs can be given names such as "A[0:7]", which indicates that there are eight signals on the arc. Each wire that is connected to that bus must then be named, for example, "A[3]" in order to make the proper connection (use the Rip Bus Signals subcommand of the Network command of the Tools menu to do this automatically). Besides providing array structures, bus names can concatenate signals from elsewhere in the facet. For example, a bus can be named "B[2:3],C,D[0:3]", in which case it contains seven signals from other vector and scalar networks.

By default, supply networks defined with the Power and Ground nodes of the Schematic technology are combined into one network. This means, for example, that two arcs, each connected to a separate Ground node, appear on the same network regardless of their actual connectivity in the circuit. Although this unification is the proper thing to do for schematics, it is not always proper for IC layout. For example, in MOS technologies, two ports exported with the "power" characteristic are not on the same net unless they are actually connected (there may be multiple power rails that do not connect). As a circuit debugging aid to ensure that power and ground networks are properly connected, Electric can be instructed to unify power and ground networks in ALL technologies, regardless of their actual connectivity. The Unify Power and Ground subcommand of the Network command of the Tools menu causes all power and ground networks to be combined. Identification of a power network is done by finding (1) a Power node from the Schematic technology; (2) an exported port in the current facet that has the "power" characteristic; (3) an exported port in the current facet that begins with the letters "vdd", "vcc", "pwr", or "power"; or (4) a port on a component in the current facet that has either of the above two properties. Ground networks use the same rules, except that the acceptable port names begin with "vss", "gnd", or "ground". This unification of all supply rails can be disabled by unchecking the menu entry. By highlighting power and ground networks with and without this option, designers can see whether all of their supply rails are fully connected.

There are other debugging facilities that the network tool provides. One is the List Ports on Network command of the Info menu, which lists all exported port names on the currently highlighted network. This list contains the names of ports at all levels of the hierarchy above and below the current facet. The facility is useful if, for example, you have propagated clock lines throughout the circuit and wish to make sure that all of the exported port names on this network have some variant of the name "phi". By quickly examining this list, you can see all of the names that have been used on the network, throughout the hierarchy.

Another debugging facility is the List Connections on Network command of the Info menu which lists all nodes that are connected to the current net. This list includes only those nodes at the ends of the net, and not the pin or contact nodes used inside of the network. The command is useful if you are at one end of a wire and want to check to see what is at the other end.


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