Sorry folks, I tried using a +/- symbol in my last mail, and it makes
numbers like +/-12V come out as 112V.  Anywhere you see a voltage that
is obviously too large in my previous mail, mentally delete the leading
"1".

Cheers,

Chuck Mauro

> -----Original Message-----
> From: Undetermined origin c/o LISTSERV administrator
> [SMTP:owner-LISTSERV@MITVMA.MIT.EDU]
> Sent: Wednesday, March 04, 1998 12:46 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [OT] RS-232 polarity, and long-distance transmission
>
> Mauro, Chuck wrote:
>
> > BTW: The true EIA spec's for RS232 define a voltage swing even
> larger
> > than 112V (I forget how large, but it's either 115V or 125V), but PC
> > supplies don't generate anything over 12V (when did they ever?), and
> the
> > larger delta V just isn't necessary.
>
> The first RS232 was +/- 25V as I recall, I think that the later A & B
> versions switched to +/- 15V, the current RS232C (current?) uses
> +/-12V.
>
> I once had the fun of playing with a newspaper photo processor that
> used a DB25 female plug the had the same (or very similar) interface
> as today's PC parallel port. But the voltage swing was +/- 25V and it
> was designed in the late 40's. Weird!
>
> --
> Neil Cherry     http://home.att.net/~ncherry
> ncherry@worldnet.att.net