> The power plane? That board has two planes (power and ground). Why > is one always the reference?
In low-voltage electronics, there is no such thing as a voltage in isolation; voltage exists only in reference to somewhere else. In high-voltage electrostatics work, there is an absolute reference, that being "electrically neutral", as in "having equal amounts of positive and negative charges". In theory, the same measure could be applied to low-voltage circuits too, but the imbalance in charge carriers is so tiny compared to the number of charge carriers involved in the kind of current flow typically involved in low-voltage circuits that it's not a useful way to look at it in practice (whereas in high-voltage electrostatics work, current flow is so low compared to the potentials built up that the converse view is more useful). In many - I'd even go so far as to say "most" - low-voltage circuits, there is only one reference, and it's called "ground". When mixing analog and digital, this is sometimes split into 'analog ground" and "digital ground", but each is still "ground" to its portion. Which is all to say that I'd say that, _by definition_, the ground plane is the reference: using the term "ground" for it is effectively saying "this is the one that's my voltage reference point". /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML [EMAIL PROTECTED] / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user