Re: Serial Fun

From: Thomas Tornblom (thomas_at_Hax.SE.remove-to-reply)
Date: 05/09/04 

Date: Sun, 09 May 2004 17:25:04 GMT

andrew@cucumber.demon.co.uk (Andrew Gabriel) writes:

> In article <70bdea73b70143849932c9b388a79834@ghytred.com>,
> <g8mqw@yahoo.com> writes:
> >
> >
> > Na, not always a MODEM. It defines "Data Communications Equipment" (DTE)
> > and "Data Terminal Equipment" (DTE). So whilst DCE includes modems, it
> > also allows for things like ISDN TA's and physical terminal switches. The
> > standard envisaged that you would have a link that went :-
> > Terminal <==> Comms <==> Comms <==> Computer.
> >
> > When we wire a terminal directly to a computer we are outside the scope
> > of the spec. Personally I think the SUN should be DTE and you should need
> > to use a "NULL Modem" or Crossover cable to connect to a Terminal.
>
> I think Sun expected that you would connect a terminal to its serial
> port to get a login prompt, whereas a PC expected that it would be
> a terminal.
>
> I think newer Sun systems' serial ports are DTEs though (I vaguely
> recall I need a crossover to connect an Ultra-60 to a PC).

Any V.24/RS232 device is either DTE (Data Terminal Equipment) or
DCE (Data Communications Equipment, and for DB25 connectors the
standard is male connectors for DTE and female for DCE.

One of very few manufacturers that got the connector gender correct
was DEC, at least in the 80:s with VT-100:s and DEC-20:s, which was
what we had at the university.

I agree with the OP, Sun has always had the wrong gender on the
systems with DB25 connectors. I believe that the newer ones with DB9
got it right though, although one may argue that it is more a defacto
standard setup by IBM for the PC.

In a perfect world, one glimpse of the connector should be enough to
know if a straight cable (male to female) is needed, or a crossed
(male to male or female to female). This seldom works in our imperfect
world. Connecting a modem to a Sun requires a straight cable with male
connectors, yuck!

>
> --
> Andrew Gabriel
> Consultant Software Engineer

Cheers,
Thomas 

-- 
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