>> - where should I connect the serial console ? There are 3 dec rj11-like
>>   connectors, and 1 db25.
>
> The console is port 3, 9600/8n1.

DECsystem 5100 has serial console on port #0.  This assignment is different
from most other DECstations.  Digital had a custom for desktop systems
like as;

	port #0		LK keyboard
	port #1		VS mouse
	port #2		communication, w/ modem control signals 
	port #3		printer, w/ or w/o modem control signals

For headless configuration, port 3 will be serial console. Some of DEC
models (VAXstation or TC Alpha) have "S3" switch to force to have
serial console on port 3.

The release note of "ULTRIX and UWS Version 4.3" has a definite figures
describing how DECsystem 5100 serial ports are labeled.  The point is,
5100 port numbering is twisted and it's very hard to understand w/o
figures.

Figure 2-1 tells, facing to 5100 backplate there are three DEC MMJs
and one DB25.  ULTRIX does number them as "3, 1, 0, 2" from left to
right.  DB25 is numbered 2 and the doco tells modem capable.  The MMJ
left of it is 5100 console and numbered 0.

Figure 2-2 tells 5100 numbering scheme for optional serial port
expansions.

- The first expansion is numbered 7, 5, 4 (left to right) for the a set
of DEC MMJs above the builtin MMJs.  DB25 on top is numbered 6 and modem
capable.

- The 2nd expansion is numbered 10, 9, 8, 11 (left to right) for the set
of DEC MMJs above AUI/BNC.

Tohru Nishimura