[NTLUG:Discuss] Switch Question

[Steve Baker]

Kipton Moravec wrote:

> This is a problem if you want to use RS-232 or RS-422 or RS-485 because 
> usually one of the lines is a ground, so you are matching ground to 
> ground through the relatively thin wire. Basically the whole building 
> will want to equalize through the small ground wire. Not a good idea.

It's always worth remembering that RS-232 was designed solely to connect
a dumb terminal to a modem or a modem to a mainframe computer.

The fact that it's convenient and ubiquitous (although it is FINALLY
showing signs of dying out) means that it's been stretched into a million
uses as diverse as connecting a mouse to a laptop or a Lego robot to a
PC.   However, none of those are remotely close to what it was designed
to do.

> However, Ethernet is already an isolated system. The people who designed 
> the standard were aware of the problem and the final component on all 
> Ethernet cards and interfaces is a little transformer to provide the 
> isolation, to prevent exactly what you are worried about.

Yep.

The way to fix it if you are insistant on using RS-232 is to use it
in the way it was always intended - over a phone line with modems.

Then you'll have all of the inherent electrical isolation designed
into phone lines working for you.  (But of course with modems,
you'll be lucky if you get 56Kbd).

---------------------------- Steve Baker -------------------------
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