Installing a SMD disk drive

Parent Category: Stories Category: My PDP-11/44 Written by Administrator

With my 11/44  also came a BA11-K mounting box, filled with 3 tape controllers and 5 Emulex SC31 SMD disc controllers. SMD (Storage Module Device) was the industrial standard disk interface around 1980, I felt I needed one some day.

Nine months later I could buy a Fujitsu Swallow MK2312K (more). It has 70MB capacity, the Emulex SC31 can present it as RM03 drive on RH11 controller.

It’s half transparent, you can see the disk platters. And you can see even more if you raise the two printed circuit boards away from the drive body. But the interesting part is the moving positioner, and he is almost completly hidden behind some air filter stuff ... nothing is perfect.




The M2312K came with an unusable fan and without power supply, so this was the first challenge: the M2312 needs -12V@3A, +5V@4A and +24V@7A. The fan runs at 120VAC, I replaced it by a 12VDC fan, so it needs also 12V@1A. I build this power supply by cascading three standard PC-ATX power supplies. They are very small and powerful , and can be found on every recycling yard. They are good at +5V and +12V, but -12V is very weak. To add the voltages, I had to remove the internal grounding. Normally logic ground is connected to external earth in every power supply, so cascading them would yield a big short cut.



The ATX-P1 connector fits into a male connector, which can be unsoldered from every PC AT or ATX mainboard (also available on recycling yards), at best with a soldering lamp.

The SMD interface has two cables: 26 pin and 60 pin flat ribbon. You can make them yourself. The final setup looks strange, but works:





(Yes, my basement is a mess!)

First test

I had no manuals for the MK2312, but they are there for the MK2322 ... close enough. I had to set geometry options on the drive to a sector size of 620 bytes the Emulex SC31 requires.

When connected to MK2312, the Emulex SC31 must be jumpered to emulate a RM03 MASSBUS subsystem, with an RH11 controller. It has about 20 registers and an built-in Format command, so you can format the drive and read error codes and geometry just by depositing and examining into controller registers. PDP11GUI was a great help at this again.

Those first tests went OK immediately.


Then things got nasty.

The Emulex SC31 emulates not a complete RM03 controller, there are some minor differences. All OSses can work with Emulex SC31, but MAINDEC/XXDP diagnostic can not be cheated. So Emulex has a long patch lists in its manual, describing how the MAINDEC diagnostics must be patched so the diagnostics can run.

Unfortunately, I could not get the original diagnostic version Emulex has patched. Neither XXDP 2.0, nor XXDP 2.5, nor those MAINDEC paper tape archives on can be used as input. So there’s no XXDP. And DEC wants all formatting and bad sector handling be done by XXDP ZRMLB1 formatter.

I made a RM03 disk driver for PDP11GUI. Reading and Writing disk images onto the MK2312 works fine. I constructed a bad sector list bei several times reading and writing the whole disk. I hoped to made a RM03 disk image with bad sector information on it with SimH, but: XXDP did also fail for SimH’s emulated RM03 hardware!