AVR-Chat

On Thu, 2005-09-01 at 07:45 +1000, John Samperi wrote:
> At 04:15 AM 1/09/2005, you wrote:
> > > Ummm - a low voltage (0v) is a logic zero. A high voltage (5v) is
> > > a logic one.
> >    Not according to AVR data sheets, it's not.
> The convention of using logic 0 for 0 volts
> and logic 1 for a high (be it 5, 1, 3 12 or 100V)
> was established before micro controller were thought
> of and therefore it has nothing to do with Atmel.

  And, like all standards and convetions, it is subject to being abused
and/or ignored by any compnay at any time.  Witness RS-232-C and IBM,
for example.

  Assuming that a zero volatge is a logical zero will get you into
trouble in some systems.   I *MAY* be mistaken abut the AVR, but I don't
think so.  When I was programming the kiosk project I refer to in
another (rather long winded) posting I made earlier, I made that error.
Couldn't figure out why my controller wasnt doing ewhat I thought it
shoudl be, until I realzied I needed to change the sense of my logic.
Switched to having ground potential read as a logic one,and Vcc as a
logic zero, and everything ran perfectly.

tom