> What, exactly does this loopback device look like?

This is the FAQ bit...  Apologies to those of you who've seen it too
many times.

>From a posting by Philip J. Tait <PJTait@iee.org> to comp.unix.ultrix
earlier in the year:
------------------------------------------------------------
Actually, you only need one little gadget - a paper clip:

To make a DecStation 3100/2100 into a DecSystem 3100/2100

1)	Remove the Graphics Board from the Mother Board.
2)	Remove the keyboard and mouse.
3)	Make a mouse eliminator.  Short Transmit data to Receive Data.
		Pins 1 -> 3 on the diagram below.
	NOTE:
	The diagram below is the view of the plug on the end on the mouse.
	The pins that are shorted are on the Decstation. Be sure to account
	for the mirroring.
	
		
DecStation 3100/2100 Mouse


	  -------
         /  | |  \  
        /   ---   \ 
       /           \
      / 4    5    6 \
     /    -------    \
     |  3 |     | 7  |
     \    -------    /
      -   2     1   -
       \           /
	-----------


NOTE: This is the view looking into the plug on the end of the mouse.
-------------------------------------------------------------

Enjoy.  I've made a few of these out of old mouses and tablets.
__
David B.