Introduction and need help bringing some pdp11's back

Chris Zach cz at
Tue Oct 29 19:37:44 CDT 2019

> I assume your building up a Qbus PDP-11.

Yup. They're easier to get going for starters and since I got rid of the 
11/44 the fastest system I've got.

> To go from RQDX3 to any drive you need a distrbution panel as used in
> BA23 or M9058 distribution board usually used in BA123.

Yup, got one of those in the BA23. Oh, are the floppies DU0/DU1 with the 
disk drive DU2 or is it different?

> The M9058 can plug in to any general slot in Qbus for power and does not
> past interrupt or DMA grant.  Bottom/end of the bus is fine.

Interesting, I didn't realize the RQDX series boards didn't use 
interrupts or DMA. Does the CPU just poll them endlessly?

> Then you need a 50 wide cable from RQDX3 to the distribution board and
> the cable to match floppy from the distribution board (usually 34 wide).

Got that. The floppy cable I have has a twist between the second and 
third plugs, but I'm using the straight section only.

> Jumper details are up to  you to slug out but I have two systems using
> the RQDX3 and M9058.  I also have the Micro PDP-11 using the ba23
> distribution.   Don't ask right now I can not get to them for the next
> month.  Drive jumpers have to be correct.

For the RX50's were there any jumpers? If I'm still fiddling with this 
in a month I might ask for a pic of the configuration.

> All of this is in the various manuals but no single one!

The RQDX3 was kind of out of my price zone the last time I worked on 
this stuff. The ESDI controller is extremely fast (and does elevator 
seeks so it rocks on RSX11) but doesn't have floppy support.

I'll see if I can dig out/find any of my RQDX1 boards to cross-check the 
RQDX3. Any of them should be able to run a RX50 (and lord be told I have 
RD52 and RD53 drives around here....)

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