VAXstation Serial Connectivity

The VAXstations I have all connect to the outside world through a DEC MMJ port.

This is a 6-pin/6-conductor cable very similar to an RJ12, but with the tab offset. Apparently Thrustmaster uses a similar jack on some of its devices.

The standard MMJ cable is a “crossover” cable, the pins on one end are offset from the pins on the other end. A straight through cable can also be used, but would require an additional “null modem” adapter if you’re using it as a serial port.

I’ve gotten the necessary crimp tools/dies and parts to make my own cables, but unfortunately I have had no success so far for reasons yet to be determined.

There are also DECserver terminal servers that use RJ45 ports. To use these with MMJ I will try making some custom cables again.

To use these with DB25 serial, you need an adapter. I got a bunch of DEC H8575-A adapters from MMJ to DB25.

If you’re using a VT320 or VT420, you can just use the (crossover) MMJ cable directly.

On the VAXstations, because they are normally intended to be used with a mouse/keyboard/monitor, there is a switch you have to set to make it boot and operate from the serial port “headlessly.”

Furthermore, I have found that at least on some of my VAXen, when I disconnect the serial cable it sends a serial break and causes the system to drop to it’s equivalent of BIOS, with a >>> prompt. So, I try not to do that.

Online Sources

There are also apparently places you can buy RJ45 to MMJ cables pre-made.

I’ve found a few sources for MMJ cables as well; I’ve put in orders from a place on eBay in the UK but you have to tell them to make the cables cross-over instead of straight.