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fedora-users: Re: Serial port permissions -

Re: Serial port permissions -

From: Bob Goodwin <bobgoodwin_at_nospam>
Date: Wed Oct 19 2011 - 13:42:56 GMT
To: users@lists.fedoraproject.org

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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