Serial port permissions -

Bob Goodwin bobgoodwin at
Wed Oct 19 13:42:56 UTC 2011

On 19/10/11 09:30, Tim wrote:
> Brian Mury:
>>> You should see +12 volts or -12 volts (actually anything between 3
>>> and 15 meets the spec, but you'll usually see somewhere around 12).
>>> Negative voltages are high, positive voltages are low,
> Tim:
>> Other way around...  A high (digital 1) is a positive voltage, a low
>> (digital 0) is a lower or negative voltage (i.e. less than the 1's
>> voltage, whether it be zero or below zero).
>> All digital logic is this way.  There are cases where the low signal
>> is the active state (i.e. a 0 is true and 1 is false), called
>> "negative logic," or "active low," but it's still a case of 1's
>> voltage is greater than 0's.  It's the meaning of 0 and 1 that's
>> inverted.
> Scratch that...  Serial *data* lines are backwards.
> Gawd I hate negative logic.

        Well if nothing else you have stimulated our thought processes!
        That's good.


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