Brian Jones writes:
>
> Tjaart,
>             for those of us without an electronics background (OK so
> you might ask what on earth are we doing on PICLIST -in my case the
> answer is 'Learning!') would you live to explain further the naming
> of Vdd, Vcc etc.
>
> >The PIC's are CMOS devices (That's why the power pins are markedVdd & Vss
> > instead of Vcc and Vee),
>
> Apologies for the off-topic bandwidth - hopefully one or two succinct
> responses will enlighten me (and other electronics neophytes) without
> infuriating others.

there are two types of transistors mentioned here - bipolar (NPN and PNP)
which have the 3 leads, collector, base and emitter. The other is the
MOSFET (N channel and P channel), which have the leads: source, gate and
drain.

The cc, ee, ss, and dd refer to the voltage at that pin.

Vcc - Collector - in a npn transistor the collector is connected to the
                  more positive voltage
Vee - Emittter  - in a npn transistor the emitter is connected to the more
                  negative voltage

Vss - source    - in a n channel MOSFET the source is connected to the more
                  negative voltage
Vdd - drain     - in a n channel MOSFET the source is connected to the more
                  positive voltage

In a TTL circuit where bipolar transistors are used, the designators Vcc and
Vee are used.  In a CMOS circuit, where MOSFETs are used (like in the PIC)
Vss and Vdd are the more correct terms.  If your power supply is 5V, it
normally goes like this: Vcc=Vdd=5V and Vee=Vss=GND.

Clear as mud, eh?

Matt


-----------------------------
Matt Bennett                |
mjb@hazmat.com              |
http://www.hazmat.com/~mjb/ |