Data Sheet

LABCENTER ELECTRONICS LTD.
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en-masse.
Connectivity Considerations
When we transfer our schematic to the PCB Layout software (netlist) all of the wires and
connections are grouped into nets and passed through. Proteus actually does quite a lot of work
for us behind the scenes at this point, automatically generating numerical names for the nets
and also assigning the net to a default ‘net class’.
Net names are assigned by Proteus according to the following rules:
A group of connections which include a named terminal will be assigned a net name
according to the name of the terminal.
A group of connections which include an unnamed ground terminal will be assigned to
the GND net.
A group of connections which include an unnamed power terminal will be assigned to the
VCC net.
Any other group of connections is given an auto-generated numerical name.
What this means in practice is that all the work is done for us here; there is no real need for us
to get involved in naming groups of connections. It is important however, that we understand the
rules for unnamed ground and power terminals. If in any doubt, you should always name your
terminals explicitly.
If a net does not have a name from a terminal you can if you wish explicitly name a net by
placing a wire label with syntax (NET=NAME). This is useful if you wish to place a power plane
on the net in the PCB and otherwise helps to distinguish the net from other nets with auto-
generated names.
A ‘net class’ is simply a group of nets which will have common properties in the PCB Layout.
Specifically, all connections in a net class will have the same trace width and will obey a single
set of rules with regard to clearances and design rules. Again, Proteus will do a considerable
amount of work for us and will assign net classes as follows:
Any net with a power or ground terminal is assigned to the POWER net class.