Am 19.05.2010 16:16, schrieb Invisible:
> While we're here, does anybody comprehend what VCC, VSS, VDD and related
> symbols mean?

According to JEDEC,

VBB = substrate power voltage (bias voltage), a voltage < VSS/GND.

VCC = logic power voltage, serving as a reference for high signal levels 
(often sharing a common rail with VDD, in which case they may be used 
interchangeably).

VCCQ = output stage logic power voltage, separate (positive) power rail 
to drive output loads.

VDD = drain power voltage. separate (positive) power rail to drive the 
chip's internals.

VDDQ = output stage drain power voltage. Effectively the same as VCCQ.

VEE = emitter power voltage. Only used for ECL devices.

VHH = special function enable voltage. An extra-high voltage to enable 
certain special functions of a device.

VPP = programming voltage. An extra-high voltage to supply the power for 
the programming function of a device (e.g. EPROM)

VREF = reference power supply, serving as a special reference voltage, 
e.g. for ADC inputs.

VSS = GND = ground reference / source power voltage, serving as both 
(negative) power rail and low signal level reference.

VSSQ = GNDQ = output stage source power voltage / ground reference, 
serving as both a (negative) power rail and low signal level reference 
specifically for output signals (should always be at the same level as 
VSS=GND).

(This is just a subset of all the symbols used; for instance, 
digital/analog devices such as programmable amplifiers or ADCs/DACs 
often use separate voltage rails for the analog signals.)

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