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When do we use Vcc / Vdd / Vss / V+



Jan 1, 1970
There seems so many symbols for the same thing
(except that Vss is GND I think) but when do we
use which ?

Howard Henry Schlunder

Jan 1, 1970
As a young person, the history behind those names seems incredibly baffling
(or stupid, not sure which). People have wondered about it before; you
might search Google Groops to try to make sense of it yourself.

Regardless though, Vcc refers to a common positive supply of bipolar ICs (no
doubt related to a collector). Vdd refers to the common positive supply of
CMOS circuits (no doubt related to a drain). Vss refers to a common ground
(no doubt related to a source and therefore CMOS as well). Vee is used to
refer to a negative supply (no doubt related to an emitter). Since CMOS is
the most common technology today, if you use Vdd and Vss to describe your
supplies you will most likely have your symbology right (although anyone
would understand you if you got it wrong, so long as you used the right
equivalent). To be the least ambiguous (and to work towards the elimination
of symbols which don't seem to make any sense), it might be best to refer to
signals as +5V or +3.3V and GND.

Howard Henry Schlunder


Jan 1, 1970
Keith R. Williams said:
I think this is the best way, particularly since several voltages may
exist on one schematic. I turn it around so all the tools understand
the nomenclature though. I.e. V5 (+5), V33 (+3.3), V5N (-5V), etc. I
have had to get inventive when I had both +15V and +1.5V on the same
board though. ;-)
Take a tip from the Europeans (resistors, caps, etc) and use 3V3 & 1V5 ;-))

Keith R. Williams

Jan 1, 1970
Take a tip from the Europeans (resistors, caps, etc) and use 3V3 & 1V5 ;-))

Some capture tools don't like leading numbers. I don't think
this is as bad as them not allowing a '-' in front of signals,
but I can use only what they allow.

Though, even VHDL is lacking a standard way of differentiating
negative active signals. BAD! BAD!