>> - what is "VDD"?
> don't know.

Almost certainly one of the power supply voltages, more canonically
spelled "Vdd".  It's the drain-facing voltage, in much the same sense
that in TTL Vcc is the collector-facing voltage.

I can't remember offhand what voltage it normally is.

And, of course, this is a generic guess; if anyone knows that in this
particular context it means something else, please, correct me!

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