App note MG575950 on Mentor's SupportNet explains the differences, as does the documentation shipped with the product. In essence a 'global' net defined using the global 'Tap' symbols is seen throughout the hierarchy where it appears without the need to physically draw the nets. If you have a Global GND on 'n' sheets in your design then they are all connected, and this is also true of any components with implicit power pins connected to GND, by implicit we mean those defined in the PDB (for the Xpedition flow) or those defined by the SIGNAL property in the net list flows.
Thanks for your reply! Is the following true assuming no hierarchy in the design: all nets including global nets are the same except for the symbol in the schematic. All nets including global nets with the same name are connected across all sheets of the schematic. An entire schematic design could be done correctly without the use of global nets of one chooses to. In this context, the use of global nets would be nothing more than a convenient way to separate out power and ground nets from all other nets.
That is correct, though the use of 'Tap' symbols to connect global nets provides more visual information to the user, for example a net pulled up to power is clearly indicated by the Tap symbol's graphic.
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