The RQDX3 is a hard drive controller for MFM drives. It can be obtained easily and cheaply. If you are lucky, you might find a manual. The information here should be enough to get one of these working.
RQDX3 boards are cheap ($20) and easy to find, but until now the only way I've seen for connecting it to a drive was via the distribution panel that is buried inside a BA23 chassis. Here is how to construct a ribbon cable that connects the RQDX3 to a single MFM drive.
As you look at the front edge of the RQDX3, with the components up, pin1 (the red stripe on a gray ribbon cable) is to the right.
You will need a 50 pin ribbon cable with a connector that will fit the front edge of the RQDX3. One way of getting this is scavenging an internal SCSI cable.
You will need 20 and 34 pin card edge connectors. These can be hard to find new, but most boxes of junk computer parts will contain a couple MFM cable sets. Carefully disassemble these connectors and remove the old ribbon cable.
If you have an RQDX3 manual, the ribbon connector pinout given in the back of the manual may be incorrect. Use the list here:
1 -- write data 1 + (second drive)
Note that there is little consistency in the origin of numbering, for example, we have DS1, 2, 3, and 4 on the RQDX3 corresponding to DS0, 1, 2, and 3 on the drive.
Here is the interconnection list for the ribbon cable:
RQDX3 34 pin connector (all odd pins are
I built my cable by "unzipping" 3-inch strands of the 50 pin ribbon cable at the end away from the RQDX3, and inserting individual strands into the correct teeth on the MFM drive connectors. When a signal in the ribbon happens to be paired with a ground, I unzipped the pair, because every odd pin on the 34 pin connector is ground. There were a few other cases where it made sense to unzip a group (for example, WD+ and WD-). Connect three RQDX3 grounds to the 20 pin connector as shown. The remaining grounds should be distributed on the 34 pin connector.
There are a couple of front panel signals that must be terminated. (You have to do this, or it won't work). For each "Dx write protect" signal, I pulled it to +5 with a 4.7K resistor. The 'Dx ready" signals can probably be terminated similarly, however, I used the following circuit:
There is a four pin jumper near the front edge of the board next to a uA9639 (an 8 pin DIP). Looking at the board with the front edge to the left, the rightmost two pins should be jumpered. This combines HD3 and "reduced write current" on pin 22. (With the jumper in the center position these functions are separated).
Holding the board with the Qbus connectors toward you, the row of 11 jumpers are bits 12 through 2 of the module address. The remaining upper bits are all ones, the lower bits all zero. With "I" meaning "jumper in", and "O" meaning "jumper out", the default setting is: IOIOOOIIOIO. This selects a module base address of 172150.
All other jumpers on the board should be out.
In theory, the RQDX3 should work with any MFM hard drive. The catch is that the drive geometry is stored on the first cylinder of the hard drive, and the DEC supplied utility (ZRQCH0 in XXDP) that puts the geometry info on the drive only supports a few drive types. It is possible to patch ZRQCH0 to define new drive types (I've done it, see XXDP), but it is nastily difficult.
Here are the supported drive types:
C=cylinders, H=heads, S=sectors per track.
The only information I've found that might relate to what's on a DEC formatted hard drive is in US patent #4,434,487 at www.uspto.gov. I didn't read it carefully enough to determine if what is described pertains to the RQDX3 or some other disk system. I did read enough to know that the on-disk format is extremely complicated and probably not worth the time it would take for me to hack it. Also be warned that there are can be subtle differences between patents and the actual implementations (either intentional, or due to further development).
There are two ways I know of to format a drive for use with the RQDX3. One is to use a utility in the boot ROM of a microVAX 2000. I have never tried this. The other is with the ZRQCH0 utility, which is part of XXDP. I have an image of ZRQCH0 that can be booted via VTserver.
From the file "third party disks.txt", is this sample ZRQCH0 session:
CHANGE HW (L) ? Y
**** WARNING ****
MSCP Controller Model: 19
Do you want to use manufacturing bad block
information [Y/N] (A) N ?
UIT Drive Name
Formatting of Drive 1 Begin.
[a long sequences of messages is displayed here, 1
per minute, showing the
Drive 1 has been formatted successfully.
Other information sources
Last modified: December 31, 2009