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fedora-users: Re: Serial port permissions -

Re: Serial port permissions -

From: Tim <ignored_mailbox_at_nospam>
Date: Wed Oct 19 2011 - 13:30:53 GMT
To: Community support for Fedora users <users@lists.fedoraproject.org>

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.

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