Randy,
In any electronic circuit, the pins of the various components that are
connected together are called a net. Generally a net connects two or
more component pins and a circuit or schematic design is a collection of
one or more nets. A schematic is just a graphical way of representing
what component pins must be connected together for the design. The
schematic capture program (editor) will assign a net name to each of the
unique nets in the design. Most programs assign the nets a numeric name
but usually allow the user to change this to something more useful like
"reset" or "clock" etc. Debugging a design is much
easier if all the nets have some functional name. Most of the schematic
capture packages that I have used allow you to draw a stub of a wire to
a component pin and assign it a net name. All stubs that have the same
name are on the same net and connected even though there is no direct
graphics line on the schematic. This is a "connect by name"
feature and is quite useful in complex designs. Things get a little
more complex when you have busses, which are sort of a short hand for a
collection of similar named nets or have a hierarchical schematic. In
high-end programs nets can be assigned various properties in addition to
just a name and are used to guide the PCB layout process. Things like
the maximum number of vias, trace width, trace spacing, layer and
propagation delay are common. With today's high-speed processors
and memory impedance control and trace propagation delay matching are
critical to proper operation. Once the design is in the PCB layout
stage these net properties can be used to guide both manual and
auto-routing of the board, they are also used for post layout design
rule checking.
Once in the PCB layout program each net becomes a copper tract (or
plane) that connects the component pins assigned to that net.
Most schematic packages will let you output a "net list" which is
usually a text file containing a list of nets in the design and the
component pins asigned. ie. ( clock: U1-4 U8-5 ) And most PCB
layout packages will accept a text file net list as input.
In additon to a list of NET's the PCB layout software needs to know what
footprint to use for a particular component. Generally, but not always,
the footprint name is attached as a property to the component symbol
used when drawing the schematic and provided to the PCB program when the
PCB program reads in the schematic.
Craig
--- In Homebrew_PCBs@yahoogroups.com, "Randy S." <rj3819@...> wrote:
>
> Whats the concept of "nets" in all this pcb creation process?
>
> Randy
>
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