I just got some pinouts from a friend of mine that works for the Digital
division of Compaq.  The pinout I have for a RS-232 adapter to MMJ is:

 25-pin            6-pin MMP

2 .............. 2   TX+
3 .............. 5   RX+
4,5
6,8 ............ 6   DSR
7 .............. 3,4 TX-,RX-
20.............. 1   DTR

This is supposed to work with external terminals.  Also, a note at the
bottom reads:

>notes:
>1.	Pins shown seperated by commas "," are jumpered together in the adapter.
>
>2.	Distance restrictions for RS232 (250 ft.) apply to circuits using these
       >	adapters.  Pure EIA-423 circuits have a maximum distance of 1,000 ft.
>
>3.	The connector TAB is offset towards pin 6.

I guess the MMJ is very close to RS-423, or at least it can detect a RS-232
connection.  Hope this helps!