Sorry Dave, It's quite possible that my head "was not on earth" when I read it (not sure why the thought came to mind). I apologize. On Sat, Nov 14, 2009 at 2:02 PM, Dave Tweed wrote: > Eric Wolf wrote: > > On Sat, Nov 14, 2009 at 8:04 AM, Dave Tweed 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. > > > > 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. > > What on earth are you talking about? > > I was referring to the -48V "battery" used on analog voice subscriber > loops. > > "Bipolar violation" is a term related to the line coding used on digital > trunk lines such at T1, E1, etc. > > Completely separate worlds; not related at all. > > -- Dave Tweed > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist