I always thought it was to cancel out any leftover capacitive voltage left
on the line which could cause bipolar violations if it were to build up high
enough.

-Eric Wolf

On Sat, Nov 14, 2009 at 8:04 AM, Dave Tweed <pic@dtweed.com> wrote:

> If I had to guess, I would say that the negative voltage was selected for
> the RS-232 idle state for the same reason that telephone lines use a
> negative supply -- to reduce galvanic corrosion of the wiring from leakage
> currents.
>
> -- Dave Tweed
>
>
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