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Re: two keyboards, two monitors, two users, one processor?

This discussion starts to be out of list's topic, sorry.
I'll send further responses only by e-mail.

If the power instalation is properly designed, it should be no problem.
However I, personally, would always prefere two have an additional "zero
current" ground wire dedicated for computers only.
And there still exists a problem with voltages induced by eg. electric
The optoisolation circuit (not very expensive, because it is
not very fast link, and for "software flow control" two transoptors
powered from unused port lines are sufficient) is much better solution.
The standard built-in serial ports, are rather delicate (Usually they are
even not compatible with RS232 standard, because they may work correctly
with 0V-5V logic levels). The professional RS232 boards should be safer.
This problem is particularly serious, when someone wants to connect two
computers using their parallel ports (and PLIP). The parallel ports are
much less protected.


On Wed, 25 Feb 1998, Britton wrote:

> On Tue, 24 Feb 1998, Wojciech Zabolotny wrote:
> > 
> > On 24 Feb 1998, Carey Evans wrote:
> > 
> > > Britton <fsblk@aurora.alaska.edu> writes:
> > > 
> > > > On 23 Feb 1998, Carey Evans wrote:
> > > 
> > > [snip]
> > > 
> > > > I think most X apps would run tolerably over a null modem cable.  If I
> > > > understand these gadgets right, the can operate at the speed of the serial
> > > > port, which is about 120 kbps, I think.  Even over ppp (33k modem) many
> > > > apps function reasonably well.
> > > 
> > > OK, you're probably right.  I forgot how much faster a null-modem is
> > > than a 28.8K modem.
> > > 
> > However using the null modem cable one must be very carefull about power
> > supply! Sometimes it is possible to destroy serial ports, when two
> > computers are connected to the sockets powered from different phases.
> > I've done it :-(.
> > The safest solution is to power both of them right from the same socket. 
> > 
> > 					Wojtek Zabolotny
> > 					wzab@ipe.pw.edu.pl
> This is exceedingly odd.  As a power engineer in training I would say
> somebody did a really rotten job designing the power supply in one of your
> machines.  Was there any other equipment on either of the machines's
> outlets?  Poor power regulation aside, I don't see how a phase difference
> affected the serial port.  I hope that in general at least this isn't a
> problem.   

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