>From my understanding, many of the older terminals and
minicomputer terminal ports used the outer limits of the RS-232
spec:
-25V to -5V is considered a "low" and +5V to +25V is considered a
"high", if I recall correctly. I know that some of the oldest
equipment that used it used +/- 24V, and that some also used +/-
12V. This would help drive signals over those longer cables, as
more voltage would mean less effect from the capacitance of the
lines, as well as fewer problems with noise.
Using only the three basic signal lines helps, too, as there's less
chance of a noise-spike-type error corrupting something, IMO.
Anthony J. Albert
On 3 Mar 00, at 1:00, Will Baldwin wrote:
> > Date: Thu, 2 Mar 2000 09:36:31 -0500
> > From: "Anthony J. Albert" <[EMAIL PROTECTED]>
> > Subject: Re: What could I do with a 100 foot serial cable?
> >
> > Not a heck of a lot. That length of cable is *WAY* out of spec for
> > standard RS-232 to deal with, especially if it's unshielded cable.
> >
>
> On a Data General minicomputer I used to work on, it used RS232 cables and
>connectors to connect the
> computer to the terminals, at 9600 bps. I know that some of the terminals were
>several hundred feet
> away. However, we only used 3 wires of the cable, send, receive, and ground. So,
>if someone only
> wanted to use those wires, they could maybe go several hundred feet. I admit
>though, that if you
> wanted to also use the other signals in the cable, maybe you couldn't go as far, I
>don't know.
>
> Also, it's possible that a Desktop computer might not provide as many amps to drive
>it, as the Data
> General did.
>
> --
> [EMAIL PROTECTED][EMAIL PROTECTED]
>
==============================================================
Anthony J. Albert [EMAIL PROTECTED]
Systems and Software Support Specialist Postmaster
Computer Services - University of Maine, Presque Isle
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