This should be public, so visible even if you don't have a FB login.
https://www.facebook.com/jserwach/posts/1804323786269276
--
Liam Proven ? Profile: https://about.me/liamproven
Email: lproven at cix.co.uk ? Google Mail/Hangouts/Plus: lproven at gmail.com
Twitter/Facebook/Flickr: lproven ? Skype/LinkedIn: liamproven
UK: +44 7939-087884 ? ?R (+ WhatsApp/Telegram/Signal): +420 702 829 053
For some time now I have had a couple of ZX Spectrum machines. Neither
works, each has a different problem. Today I got one of them out for another
look. The problem with it is that it seems to constantly reset itself, you
see the copyright screen briefly and then it disappears (the TV screen shows
the usual "snow" when there is no signal). It just cycles round doing this.
I put a logic analyser on it as well as a scope. The CPU Reset pin looks
fine, it goes high and stays high.
The logic analyser shows that it is happily reading code from the ROM during
the boot sequence and it will suddenly start fetching instructions from
address 0 again, this appears to be somewhat random. I don't have a lot of
experience with logic analysers, and I have found that some pod/probe
combinations cause the machine not to work at all, so the logic analyser is
not, unfortunately, above suspicion. However the behaviour I see appears
consistent with what the logic analyser is telling me.
My thoughts are that this must either be a bad Z80 CPU or a bad ROM. Neither
is socketed and I am reluctant to desolder ICs unless I really have to as
there is always a risk of damage to the board.
Has anyone seen a similar problem before? Could this indeed be the CPU or
the ROM, or could there be a different cause?
Regards
Rob
Hello PDP-11 crowd:
I?m thinking of starting a project that will interface to a DR11-C, which has the usual 40-pin Berg ribbon cable connectors. I thought I?d ping the collected wisdom here to see if other folks had already sourced an available modern cable connector for this that they particularly like?
cheers,
?FritzM.
Even though I've been quiet, I have been making slow progress on the
QSIC in the background.? For those who've forgotten what the QSIC
project is about, here's the description:
http://pdp10.froghouse.org/qsic/html/overview.html
We've been working away on getting communications with the SD card
working and that's basically there now.? It initializes and reads and
writes blocks.? I've also connected it through an async FIFO to the
minimal RK11 controller I had working before and that's mostly working.?
That is, it can read and write blocks under control from the QBUS PDP-11
as if it were a real RK11/RK05.? What more could you ask for?
Well, I could ask for a lot more really but that's pretty good.? There's
a lot of RK11 functionality that I haven't implemented yet and all sorts
of configuration options we need to get in there.? Also, there's a bug
where it sometimes scrambles data so it's not quite ready to boot and
run a real OS yet but it's getting awfully close.
Here's a picture to my test setup:
http://pdp10.froghouse.org/qsic/qsic-setup.jpg
And a picture of a test of some spray-on glass frosting used as a light
diffuser on the indicator panel.? In this picture you can also see the
new LEDs I found that are a much better color match to the old
incandescent bulbs than the LEDs I picked for my first attempt.
http://pdp10.froghouse.org/qsic/frosting.jpg
Now for the request.? I've decided that I'd like to put a soft-processor
in the FPGA to handle a bunch of things (configuration duties and the
USB protocol being two of the big ones).? My preference would be for
this soft-processor to be a PDP-11.? Surely there's hack value in using
a PDP-11 as the I/O processor for a PDP-11 but there are practical
advantages to this as well.? For one, we're already familiar with it and
have a suite of development tools.? Also, I can re-arrange the I/O
devices I intend to give to this soft-11 and put them directly on the
QBUS instead and do initial development there.
I'd rather not get diverted by yet another substantial development
project so I'm looking for a decent little FPGA implementation of a
PDP-11 that I could just pick up use for this purpose.? Something that's
already debugged.? I'm thinking closer to an 11/04 than an 11/70 and
likely just running out of block RAM on the FPGA.
Thanks for any pointers to such an implementation and thanks to everyone
who's given support and assistance as Noel and I have poked along on
this project.
Dave
> From: Ethan Dicks
> The rod is also smaller by quite a bit, but I don't have one in front
> of me to measure.
The two feet are quite different. The smaller one on the extender is 5/16"-18
(i.e. UNC Coarse thread); the larger one under the cabinet is 1/2"-13.
Replacements can easily be had from Vlier: Vlier part numbers are FSE302S
(for the extender feet), and FSE306S (for the main feet).
We really ought to do a group bulk build of the extension castings; if we get
a reasonable size order together, they shouldn't be that expensive. Ditto
for the special bolt needed to hold them to the H960.
Noel
I'm in need of some feet for my H960s and am intending to make a few pairs, so I thought I might
as well try and make them look close to the originals.
I have a few ideas on construction, for instance 3mm steel plate laser-cut and folded jigsaw fashion
then welded, or even simpler a basic welded steel bar with a 3D printed leg cap for asthetics.
I've been unsucessful in finding any closeup photos or drawings of these things so have used a diagram
>from one of the 11/70 manuals which is the best I have so far. Thankfully they drew it in isometric so
it was easly to overdraw in CAD and project it to this:
http://web.aanet.com.au/~malikoff/pdp11/DEC_H960_stabiliser_foot_left_A-H95…
I have some questions-
Does the (optional?) sheetmetal kickplate play any role in securing these legs to the frame?
Are the two front screws are only there to hold them on and there is some internal box section that goes
into the front of the channel on the rack to take the weight?
Is the outer side tapered? It looks straight.
If the foot a one piece casting (presumably) or fabricated in some way?
Is the foot pad thread in the centre of the front of the leg, and is it the same thread and pad as the H960?
Finally I would really appreciate if someone could run a digital caliper over one, and fill in my required
measurements A through Q in the above drawing. And if you have a radius guage that would really be great.
As usual, thanks for any help or advice.
Steve.
Just curious...can anyone id the system that used these two types of core
memory? I am thinking the first is a hand-made custom core, but the 2nd is
definitely from a commercial system. Looks kind of IBM-ish but it's
nothing I can ID. It's not an IBM 1401 I don't think.
http://vintagecomputer.net/core-memory/
Thanks
Bill
> From: Toby Thain
> If the documentation is good enough, people in the community will be
> able to provide the software.
You mean, host drivers?
Yeah, that documentation will be pretty trivial: 'there's this extra
register, just like the one in the RLV12; the top 6 bits of the DMA memory
address go in there - the bottom two bits are mirrored into the two extended
memory bits in the CSR'. For the 'extended' RP11, not much more than that.
If you mean the 'software' for additional controllers - that would be a _lot_
harder (plus to which it's an entirely different tool-chain, yadda-yadda).
'Use the source, Luke!', I'm probably afraid...
Noel