test-drb

test-drb@ccmp.vtda.org

101090 discussions

by robert.jarratt＠ntlworld.com

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

8 years, 8 months

40 pin Berg cable connector recommendations for PDP-11 projects?

by fritzm＠fritzm.org

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.

8 years, 8 months

QSIC update and request

by dab＠froghouse.org

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

8 years, 8 months

DEC H960 stabiliser feet. Have some questions.

by jnc＠mercury.lcs.mit.edu

> 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

8 years, 8 months

Sellam's Manual, Book, Magazine and General Documentation Sales Thread

by sellam.ismail＠gmail.com

Greetings from the piles! I've created a new thread on the VCFed forums for listing manuals, books, magazines and general computer related documentation. The thread is here: http://www.vcfed.org/forum/showthread.php?61380-Sellam-s-Manual-Book-Magazi… Thanks! Sellam

8 years, 8 months

DEC H960 stabiliser feet. Have some questions.

by steven＠malikoff.com

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.

8 years, 8 months

ID some core memory

by billdegnan＠gmail.com

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

8 years, 8 months

New DEC and other items for sale from Sellam's collection

by sellam.ismail＠gmail.com

Hello Folks, a most glorious and blessed new year to you all. I have created a new DEC sales thread on the VCFed forums and populated it with a batch of newly listed DEC cards: http://www.vcfed.org/forum/showthread.php?61371-Sellam-s-DEC-Hardware-Softw… I've also reduced the price of this nice PDP 11/03 basic system to $140: http://www.vcfed.org/forum/showthread.php?57667-LLNL-LSI-11-Homebrew-system… I've also listed a few more items, an APL and standard bare keyboard, and a homebrew front panel board: http://www.vcfed.org/forum/showthread.php?58709-New-Items-For-Sale-Check-th… As a reminder, I also started a S-100 thread for S-100 related sales: http://www.vcfed.org/forum/showthread.php?61192-Sellam-s-S-100-Hardware-Sof… Inquiries directly to me via e-mail get the fastest response. Thanks! Sellam

8 years, 8 months

QSIC update and request

by jnc＠mercury.lcs.mit.edu

> 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

8 years, 8 months

Help diagnosing boot issue SWTPC 6800

by mail.nickallen＠gmail.com

Hey everyone, Happy New Years!? I am thankful for an active community that enjoys helping each other learn, and today I am coming with an ask for help. I have a SWTPC 6800 and ADM3A terminal, I can get it to boot, and when it boots it will continue to boot for several hours.? But getting it to successfully boot takes upwards of 100 power OFF and ON cycles.? The other 99 times, I get a continuous stream of random ASCII characters (see video link below).? It's my first time seeing this type of issue that happens intermittently, and wondering if anyone has any insights in what might be causing this.? I suspect its a faulty IC on the Processor board that resets or controls the OS reset, will need to deep dive and diagnose, but thought I would ask for some direction first. https://www.youtube.com/watch?v=Ci4vhPn-3PE Thanks in advance! -Nick

8 years, 8 months

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test-drb