I have done this type of things for metrology applications on 
industrial lasers and ion beam implanters. Very low leakage required 
and able to survive a high voltage discharge. We test at 25KV air and 
contact discharge for ESD.


At 04:05 AM 2/1/2010, you wrote:
> >However, what do you do if the lines can have different
> >voltages and won't tolerate a high series impedance (>10 Ohms)?
>
>You mean apart from why you need such flexibility ... ??
>
>I guess you could use something like a bunch of DG201 type multiplexors,
>provided you kept things like the RS232 lines within +/-12V. Using suitable
>series TVS clamps should be able to limit input voltage excursions enough to
>protect them.
>
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Larry G. Nelson Sr.
mailto:L.Nelson@ieee.org
http://www.mchipguru.com

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