Subject: Re: pinout for serial console cable
To: Kevin McQuiggin <>
From: Gunnar Helliesen <>
List: port-vax
Date: 04/26/1996 03:14:15
On Thu, 25 Apr 1996, Kevin McQuiggin wrote:

> At 02:34 PM 96.04.25 +0200, you wrote:
> >I'm searching for the pinout of the serial console/printer cable for 
> >VAXstation 3100, which might be the same as the one used for
> >eg. DECstation 3100.
> I don't have the answer, but it's a good candidate for the FAQ. 
> Gunnar, I suggest this get added once the answer arrives.
> Kevin

I think the answer did arrive (at least in my inbox, a few hours ago):

-------------- included message ----------------------------------

Date: Thu, 25 Apr 96 17:05:57 +0200
To:, port-pmax@NetBSD.ORG, port-vax@NetBSD.ORG
Subject: Re: pinout for serial console cable 

Looking at the MMJ jack:
        | 1 2 3 4 5 6 |
         ---------.  .

        Posit# Description              Corresponding RS232
         1     Data terminal ready              20
         2     Transmit (+)                      2
         3     Transmit (-)             ---\___  7
         4     Receive (-)              ---/
         5     Receive (+)                       3
         6     Data set ready                    6

...or the plug...

                                ____________ this is the clip-thing that 
                                |               it in the socket...
                -----------|     |--
                |          |_____| |
                |                  |
                | O  O  O  O  O  O |
                  1  2  3  4  5  6

As you can see, it's kind-of a differential setup, which actually isn't all
that dumb.  It's just that we seem to be the only ones using it :-). (not to
mention that important signals arn't there...)

Rob Urban

---------------- end included message ---------------------------

At least I think this is the answer. It depends on what Bertram was 
really asking for...

The VAXstation 3100 doesn't use a _special_ cable to allow the use of a 
regular terminal as console, instead there's a dip-switch (accessible 
from the rear of the machine through a small hole in the cabinet) that 
allows you to set the machine in one of two modes:

- VAXstation 3100 with graphics console
- VAXserver 3100 with regular console

Note that mode two is VAXserver, not the regular MicroVAX. The difference 
is that the VMS License Manager will allow you to install a multiuser OS 
license of type (e.g. the "Activity" key on the license) 'C' (VMS Concurrent 
User) on a MicroVAX 3100, but only a type 'B' (VMS Server) on a VAXserver 
3100. The 'B' license is a single-user license, you could not a install a 
type 'C' multi-user license on a VAXserver CPU if you tried (but then 
again, there's more than one way to skin a cat... ;-)

I guess what the dip-switch really does is set the CPU type reported to 
the OS if it cares to ask (e.g $getsyi("CPU"), $getsyi("HW_NAME") and/or 

The message from Rob Urban above describes the standard pinout for an MMJ 
jack, it's the same cable you would use to connect to any DEC equipment 
using these plugs (for example the DECserver 90, the CXA16 terminal 
multiplexer and many more). The pinout is also the same for the more 
standard jacks with the "lip" located in the middle:

                          ____________ this is the clip-thing that
                          |            holds it in the socket...
                -------|     |------
                |      |_____|     |
                |                  |
                | O  O  O  O  O  O |
                  1  2  3  4  5  6

This jack is used by many other companies, Emulex terminal servers come 
to mind... I think even DEC has started to use this jack lately.

So, if Bertram was asking how to connect a terminal with a DB25 connector 
to a VAXstation with an MMJ jack then the answer lies in Rob Urban's 
message. However, if the question was "how do I get the VAXstation 3100 
to _not_ use the graphics display as console but use MMJ jack # 1 as 
console instead", then the answer is: There is no special cable, use the 



PS. Might be FAQable either way. I'm really pressed for time at the 
moment, but an update of the FAQ is overdue. I'll see what I can do... DS.

Gunnar Helliesen   | Bergen IT Consult AS  | NetBSD/VAX on a uVAX II
Systems Consultant | Bergen, Norway        | Jaguar Enthusiast/Ford owner   | | Vicki who? What .sig virus?