Chapter 6: Advanced Editing
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6-9: Networks
6-9-1: Introduction to 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 export of a single node.
Because networks are stored in the Electric database,
they can be immediately accessed when needed.
Whenever a port on a node is selected,
the highlighting indicates the entire network that is connected to that port.
Another way to see an entire network is to use the Show Network
command (in menu Tools / Network).
This will highlight all arcs on the currently selected networks.
Repeated use of the command causes the network to be highlighted at successively lower levels of the hierarchy,
useful when cell instances are part of the network.
The command will also "cross-probe" by highlighting networks that have the same name in other views of this cell.
Cells that are imported from other EDA systems often have no connectivity information
and are built with pure layer nodes
(see Section 6-10-1 for more).
When the Show Network command is run on such cells, it quickly extracts the information,
then displays it.
Also, if a cell instance is selected but no individual port is selected (such that there is no single network selected)
then the command highlights all wired ports.
If the design is very dense,
you can select one or more networks by name with the Select Object...
command (in menu Edit / Selection).
The Show All Networks command (in menu Tools / Network)
highlights every network in a different color (useful if there are not too many nets).
There are many commands in the Tool / Network menu that give information about the networks in a cell:
- List Networks shows a list of the networks in the current cell.
- List Exports on Network lists all export names on the currently highlighted network.
This list contains the names of exports at all levels of the hierarchy,
above and below the current cell.
The facility is useful if, for example,
you have propagated clock lines throughout the circuit and wish to make sure that all of the export
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.
- List Exports below Network lists all export names on the currently highlighted network.
This list is similar to the one generated by List Exports on Network
except that it works only on cells below the current one.
- List Connections on Network lists all nodes in the current cell that are connected to the current network.
This list includes only those nodes at the ends of the net,
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.
- List Geometry on Network lists all geometry in the current cell that is connected to the current network.
This reports the area and perimeter of all attached layers.
- Calculate Network Quality analyzes the currently selected network for length, area, and via usage.
- List Total Wire Lengths on All Networks lists the lengths of all networks in the current cell.
- Show Undriven Networks lists all networks in the current cell or below it in the hierarchy that
are "undriven."
An undriven network is one that does not connect to the source or drain of a transistor.
