Hi,

> >I have no practical experience of this, but ....
> >.
> >At 19200 bps a wavelength is C/19200/K
> >where C is 3 x 10^8metres/second and K is a velocity modifier.
> >For K = say 3,  a wavelength is about 5000 metres.
> >I'd say your  eg 30 meter stubs are going to be fairly harmless.
> >.
> >But then, as Carl Sagan was won't to say, I may be wrong.

Doesn't the rise/fall times also play a role in the severity of
reflections?  I remember something about a rule of thumb saying if the
rise/fall time is shorter than twice the propagation time then
transmission line theory must be applied.
>
> We installed a lot of 485 networks for banking equipment that ran 485 at
> 19200. (or slower)
> Never saw a problem related to reflections, and actually, it appeared that
> the termination resistors were hurting rather than helping. The reflections
> were over with so fast, that the resistor's main effect was to cut the
> signal level in half. I think they may help damp out noise pickup though.
>
> If you don't have real uarts, then a weak pull to +5V on one line and ground
> on the other will help cut down on the idle-state "chatter".
>
Do you mean by real uart a uart that oversamples the input and decides on
some majority rule?  If all transmission line effects die out within the
first 10-20% of each bit, then one should be safe.  As long as the
tranzorbs can taken care of the over and undershoots.

Thanks,
Niki