On Sun, 16 Jul 2000, Michael Kukat wrote:

> Hi !
> 
> On Sun, 16 Jul 2000, Rink Springer wrote:
> > I was wondering how long the console cable of my VAX 4000/300 can be... I
> > want to hook it to a terminal in my room, which is about 50 meters away from
> > my VAX. Is this possible? I think it is, but I just want to be sure :)
> 
> Usual serial ports end up at about 10 meters, but DEC uses RS-423 or so, which
> is 20mA differential.

RS-423 is differential, true. But I'm not sure the console port uses 423.
Anyway, I don't remember it being current driven, but I might be wrong.

> If you really use DEC gear, like a VAX and a VT420, you
> should just try it.

He should. But a VT420 is definitely not a RS-423 device.

> But if you have a standard RS-232 in the way, you might
> start getting in trouble at 10 meters, and even with shielded cable, you will
> not come over 20 meters without errors.

Not so. RS-232 is specified for 15 meters. I've run 20-30 meters without
any problems at all, and would not be that surprised if 50 meters worked
just fine as well.

> You can put a line booster into the
> way, or you could try to find some old SRMs (short range modems), these are
> small boxes which need no power and can make something over 1000 meters at
> 9600 Bps or so.
> 
> So: the easiest way is to use differential (original DEC-stuff), no other
> thing is in those SRMs.

Well, you'll have problems finding cables wired for differential
communication, and I don't think all DEC equipment really do it.
The DB-25 on DEC terminals is only RS-232 as far as I remember.
Unfortunately all my documentation are in boxes right now so I can't check
this up. Anyone with the docuemntation nearby?

	Johnny

Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt@update.uu.se           ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol