Cheap board guy

[Mark G. Thomas]

Hi,

On Fri, Aug 21, 2015 at 03:00:25PM -0400, Noel Chiappa wrote:
>     > From: Mark G. Thomas
>     > 4x M8192 - KDJ11 (AA or AB?) -- two work, two fail POST
> 
> And alas, we don't seem to have any prints for that card (although we do have
> what amounts to a tech manual, so maybe we can create a set, with a certain
> amount of tracing with an ohmmeter), so at the moment, at least, fixing them
> isn't so easy.

I lucked out. One of the dead ones had a broken trace on the bottom,
and cracked corner of the socket for one of the big square chips. 

The second one started working after I simply re-seated the two square 
chips around their sockets.

>     > I was hoping I could boot XXDP or RT11 from an RX33/RQDX3. The
>     > RX33/RQDX3 works in my 11/53
> 
> Well, that's a very good sign...
> 
>     > Since none of this has a bootstrap, I run the bootstrap from ROM
>     > provided by a Dilog SCSI card here, but typing "DU" or "DU0" at the
>     > prompt spins the floppy ever-so-briefly, then kicks out an error about
>     > no boot media found. Suggestions? Maybe I should try other bootstrap?
> 
> Definitely; the code on the Dilog card might not support that controller
> properly (even though it seems to recognize "DU").

Ok. Next step is try real DEC bootstrap code.

>     > I'm a little confused about what should work and what should not work,
>     > with just the 18 bit qbus.
> 
> If you have less than 256KB of memory (so Q22 processors won't wrap around,
> when trying to size memory, and think there's memory there above 256K -
> although Q18 memory probably will stop responding at 248KB, anyway), pretty
> much everything _should_ work, I would think. The high address lines being
> put out by the processor, DMA devices, etc should just have no effect.
> Although the details get tricky...

Well, now both my 11/23 and 11/73 CPUs work with the MSV11-DB cards.

> E.g. if you don't have BDAL18-21 for a Q22 memory card, what will its bus
> interface do when faced with those lines, which aren't driven in any way -
> _especially_ not pulled up by terminators? Some DEC memory cards (e.g.
> MSV11-L, M8059) have jumpers to run in either Q18 or Q22 mode, to work around
> this.

Eventually, I'd love to get one of these running 2.11BSD, with a KDJ11
CPU and a Clearpoint(?) Q22 memory card from my 11/53. I'm thinking I can
make a plexiglass shell to show off the cards, and it will be small
enough to fit on my desk at work, if I commit the sin of putting a 
switching supply in it.

>     > Do I need to wire wrap the additional address lines to be able to do
>     > anything with these KDJ11 CPUs?
> 
> No, if you have less than 256KB of memory, the high bits should just be
> ignored (I think - I haven't actually tried this, to be absolutely sure).
> 
>     > Does anyone have good instructions for this modification -- I'll
>     > probably want to do it. Do I just add the additional address lines, or
>     > are there other considerations?
> 
> I have modified an H9273 backplane (Q18) to H9276 (Q22), and it works fine;
> all I did was bus all the BDAL18-21 pins together: pretty easy, as it's a
> Q/CD backplane, not a Q/Q - just run a wire down, and solder it to each pin
> as it goes (those backplanes don't have the pins stick out far enough for
> wire wrap).
> 
> Q/Q will be only slightly more complicated (since you have to bus down one
> side, then run the signals up and across to the top of the other side, and
> then bus them in turn - do it this way, to avoid creating a branch in the bus
> which will encourage reflections); I have done this mod on a Q18/Q18
> backplane (a Sigma Q18/Q18), but have yet to actually try it.

These backplanes are just "Q/" -- they are double connector (single card) wide.
They have long wire wrap pins, so it should be easy.

> The only complication might come with termination/pull-ups. Not all
> backplanes have these built in (e.g. the DEC H9273/H9276 don't). But you
> might not need them - IIRC both the 11/23 and 11/73 have on-board termination
> which will pull the lines up. But if you _do_ need them... best bet, unless

There are terminators soldered onto the backplanes, or rather one of the
two, since someone modified it to bus them together and unsoldered the 
terminators from the one. I'll put them back when I split these backplanes
apart.

> you want to start soldering resistors to the backplane, is a terminator board
> with Q22 pullups. That's a whole separate discussion which I will leave for
> the moment... :-)

Mark

-- 
Mark G. Thomas (Mark at Misty.com), KC3DRE