Combination and Orientation of RQDX boards in one PDP-11/23 PLUS

from the US and I couldn't access them until now for cause of some problems

On 21/06/2009 20:08, SPC wrote: As far as I can imagine it appears that they were used in one PDP QBUS That would make sense; the M7513 is an RQDXE extender, used to allow you to connect an external set of drives as well as the internal ones handled by the distribution board. Unless you want some drives in the host enclosure and one or more in an external one, you don't need it. Finally, the RQDX comes with MFM cables but too with one standard floppy No. PCs are the only things that use the crossed cable. Other systems would normally not have a cross, but would have different jumper settings on the floppy drives for the drive selects. * I have a couple of RX33. Must I use TWO cables (one per floppy unit) ? No, you can use a simple bus arrangement with two connectors in parallel -- but set the DS jumpers on the two floppies so one is DS1 and the other is DS2 (that's assuming you count DS1...DS4. If the links are labelled DS0...DS3 then set the first to DS0 and the second to DS1). Don't use a PC cable with a twist; it doesn't do the right thing. You need quite a late version of firmware in the RQDX3 to support RX33s, though. * Same question with the MFM disks If you're using the M9058 distribution board, the easiest way to do it is to use one 34-way cable and one 20-way cable for each fixed disk (ie for two fixed disks, two pairs of cables). * What is the orientation of the RQDX ? I imagine it with the connectors > side turn down because turning it up would be a problem with the previous > board in the BA11-SB Do you mean the RQDX-E? Just don't use it unless you have to. The M9058 distribution board is meant for a BA123, and has its own slot at the bottom of the backplane where it's not in the way. It only takes power from the backplane, no signals, so it can go way below anything else without having to worry about grant continuity or bus termination. Look at the PDF files at http://www.dunnington.u-net.com/public/RQDX/ and specifically at M9058_layout.pdf because that will show you what needs connected. Regard an RX50 as being equivalent to a pair of RX33s, at least as far as the interface connections are concerned, so it (or the 2 x RS33) connect to J11, and your first fixed disk as RD1 so it connects to J1 and J5. Set the drive select on any fixed disk in this setup to DS3. J12 connects to the RQDX3 via 50-way ribbon cable, and J9 connects to the front panel switches. You probably don't have those, but if you look at the diagram in RQDXn_LEDs_switches.pdf you'll see that it would be easy to construct a substitute, and if need be, just use a couple of pullup resistors to ensure the drive is ready and write enabled. If you want to see more, fetch the "microPDP-11 Maintenance Manual" from the net, and look at the chapter on storage devices. -- Pete Peter Turnbull Network Manager University of York