pins 3 and 4 on the MMJ should both go to pin 7 (ground) on the RS232. 
The 423 interface is differential, unlike RS232 which is unbalanced. 
Voltages are compatible, as is the signalling modulation. in lieu of the 
real return on the 423 side, use the ground. 

happy hacking,
isildur

On Mon, 23 Aug 1999, Lehle Wolf wrote:

> First I installed NetBSD 1.4 on a PC. Now I'm trying to netboot a VaxStation
> 3100 from this PC, because the boot disk for the VaxStation is not working
> properly :-(
> What's missing now is a terminal connected to the VaxStation to monitor the
> net-boot-process. Therefore I've manufactured a cable:
> 
> 
> VaxStation:                                       PC:
> 
> ---------------
> I             I  1 - DTR (Data terminal ready) ...   6 - DSR
> I 1 2 3 4 5 6 I  2 - TxD (Transmit data)       ...   2 - Rx
> I             I  3 - GND (Signal ground)       ...   5 - Gnd
> I             I  4 - RxC (Receive common)         
> ---------I    I  5 - RxD (Receive data)        ...   3 - Tx
>          ------  6 - DSR (Data set ready)      ...   4 - DTR
> 
> I connected this cable to an additional PC. Used the Windows98
> hyperterminal, a freeware terminal program, an Amiga-Terminal program, wrote
> an own simple terminal program. Tried the configurations with/without
> handshake, changed baudrate stopbits etc.
> But the only thing that's equal to all terminal programs is that I receive 3
> (three !) characters (seens to be garbage :-( ) and then nothing happens ...
> 
> Could anyone be so kind to support me so I can quit the quest against the
> serial
> wind mills.
> Is this cable ok ?
> What are the correct transfer parameters (9600,n,8,1) ?
> Handshake required ?
> What is a RxC (Receive common) line ? Is one receive line not enough :-) or
> is it a pecular ground line for the receive channel ?
> 
> Wolf
>  
>