Recent content by Michael Robinson

I am coming back to report that after some extensive exploration, I have ultimately succeeded at fixing the problem that started this thread! As is usual in "our trade" here, thanks to @Al Kossow for bitsavers! Although I found no circuit-level documents, the key info I needed was in an old...

Good writeup! I have noticed on my 11/45 that erratic behaviors are sometimes caused by power supply voltage issues, including the machine "trying" to run when it should be HALTed. Usually this involves problems with corrosion at the connections to the harness. I added a bank of digital...

I think your FORTRAN IV code is correct, so there is something else at work here. I made two minor syntactic changes to your code so that it now compiles on my PDP-11/23 using DIGITAL FORTRAN IV, namely (1) WRITE (10,xxx) -> TYPE xxx, and (2) changed double quotes to single quotes. Given...

I've thought about this as well, since OpenBSD 5.8 does have the appropriate driver and it "mostly" works. That is why I've been using OpenBSD 5.8 on my VaxStation 3520, at least until the DSSI on its L2003 board died recently. The codebase between OpenBSD 5.8 and the most likely insertion...

Hi all, I have a VaxStation 3520 that seems to have gone through several L2003 I/O modules over the years. This is a board whose job is to run the DSSI/SCSI, serial console, network, and a few other items. At this point, I have four such boards, all with different kinds of failure... none of...

Paul correctly notes that with Unibus, you can put the memory "wherever you like" physically and it will "work" assuming you configure it correctly, with one major caveat. Read the manuals carefully! The caveat is that for "fast" semiconductor memory on the 11/45, there is a dedicated set of...

That is what I would have thought, and while the UCxx manual (on bitsavers) doesn't outright say that the UC07-III will not work in a QBUS PDP-11, it implies that there's some difference. On page 4-3, it seems to imply that the difference could be mostly physical, stating The manual is pretty...

I have three of these kind of boards, of both versions. 1. I have a UC18, a dual-ported UNIBUS version in my PDP-11/34. It works great with a SCSI2SD. I usually run RT-11, though have also played with RSTS/E. I keep meaning to attach a SCSI tape drive to the other port, but haven't gotten to...

I concur! I've done this approach many times and even recall seeing it detailed in a DEC maintenance manual somewhere. I only got in trouble once, but that was because I stole my dedicated side cutters from our bathroom without informing the other inhabitants of my house... the cutters were...

Indeed. I don't know about the MicroVAX 2000 specifically but NetBSD doesn't support all the early DSSI SCSI chipsets. I've got a VAXStation 3520, the SCSI for which NetBSD does not support, even though the CPU is supported just fine. OpenBSD does support the DSSI SCSI, so that is what I'm...

True, NetBSD does not support the DSSI disks. But if you don't mind an older version of OpenBSD, that might work instead. Even though the driver codebases between NetBSD and OpenBSD are similar, they are not identical. See: https://www.openbsd.org/vax.html It looks like OpenBSD 5.8 supports...

If you don't mind the lack of sign, you can just wire the meter for -15V "backwards". My PDP-11/45 came to me without a power supply (a blessing in disguise, I suppose), so I built a switcher for it. I got several of these meters, so that all the voltages read out on a single panel: ... and...

MIT apparently made a similar board for UNIBUS PDP-11s, and called it an MB11. For "Memory Break", though perhaps as a nod to the PDP-8 MARS panel, the device is referred to as a "MAR" in other places. Instead of halting the processor on a specified address, the MB11 triggers an interrupt...

An update on SITS archaeology, for those interested... I was wondering how SITS allocates memory across processes, and how the memory-resident RUG debugger works. The documentation for RUG states that it is a swapping debugger, and will load/unload itself as needed from a protected copy on...

Ah! You solved a mystery I forgot about. As a child, my family had an Atari 800XL. I distinctly recall the sound of loading things from floppy, but never connected the audio chip with disk accesses. At the time, I thought the sounds were "added for effect" rather than being a "side effect"...