Jasen Betts wrote in a message to Roy J. Tellason:

 PR>> I know a lot of interfaces have cheated, but RS-232 is supposed
 PR>> to be +v to -v, v=5 to 15v or so.

 RJT> I think that's about the only thing that uses the -12 supply any
 RJT> more,

 JB> I've got a VGA card here that doesn't produce a usable signal
 JB> without -12V

Oh?  News to me,  but then a lot of hardware surprises me these days.

 RJT> and even there,  the task of generating a few mA of -12
 RJT> with a chip is real easy these days,  has been for a number of
 RJT> years...   See "max-232" and similar chips

 JB> yeah, they produce about -9.5 which is close enough I guess., 

Eh?  I didn't know that they produced any specific voltage,  guess it's
been too long since I looked at the data sheets for any of that sort of
stuff.  I have one of their catalogs on cdrom,  but it gives you the data
in pdf format, which I find inconvenient,  so I don't refer to it often.

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