test-drb February 2009

test-drb@ccmp.vtda.org

196 participants
309 discussions

by ajp166＠bellatlantic.net

> >Subject: Re: 8088 vs. 80c88 > From: "Chuck Guzis" <cclist at sydex.com> > Date: Tue, 24 Feb 2009 03:29:14 -0800 > To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org> > >On 23 Feb 2009 at 18:36, Allison wrote: > >> That it had bugs, can't argue that. They could have just as easily given >> it the base uCOM78 instruction set instead. But how many V20s were bought >> to run 8080 rather than as a faster varient of the 8088? > >To be certain, almost all of the publications that I saw touting the >V-series chip emphasized the performace aspect. Few even mentioned >the 8080 emulation mode. I was surprised to see emulation extend to >the V40 and V50 uPs. > >And almost none mentioned that the V20 implemented many of the 80186 >and some of the 80286 instructions. > There was that too. >I've heard reports where the V20 doesn't work as a drop-in >replacement for an 8080. Must be just enough timing difference that >one works and the other doesn't. > True also. the original IBM PC didn't run it, as well as any cpu other than intel. Seems there was a minor timing issue that the intel part tolerent of but no one elses would work.. rumor was it was deliberate. But most of the 8088 designs were not well cooked and werern't so reliable. Allison >Cheers, >Chuck

15 years, 9 months

8088 vs. 80c88

by les＠frii.com

1) I can attest that the V20 runs cp/m80 (2.2), wordstar, word master, asm, mac, load, ddt, collasal cave adventure, logicalc. I just verified these things yesterday. 2) Here's the one with JRT Pascal (IIRC): LXI SP,LABELX CALL LABELX LABELX: ... Does the 8080 decrement the sp before it pushes the return address, or after. If its after, that code would of course not work. I can't remember which order that happens in, although I suspect that it decrements before pushing. Another possibility (seems more likely) is that the loading of the stack pointer is not finished before the next instruction is executed. I am trying to remember which register was used for the sp in the emulation mode. (I think it may be BP????) In this case, as long as some instruction gets executed between lxi sp,xxxx and the first push/pop/call, it may not show up. In any case, this seems like a rare issue, as most programs (thats a big undefensable statement) would set the sp when they start, and then leave it alone. Related, I found a bug in Spellstar for DOS. It worked fine on an 8088 or 80286, but crashed on a 386 (it could have been a 486). Here is what the code did: 100 mov dx, address of routine to jump to 103 mov [121],dx .. .. .. .. .. 120 jmp 0000 This little piece of self modifying code worked great until the instruction queue in the cpu became large enough that the jump instruction was already in the pipeline before it was modified with the desired address. I was able to fix this with a jmp dx instruction, but compilers do generate odd code sometimes. The question becomes, did the 386 have a bug, or is this just a software issue? Les

15 years, 10 months

VAX cables for the cost of postage

by pcoghlan+cctech＠vms.eurokom.ie

> >> A weird DEC cable, DB25 male on one end, and what I think is QBus >> female on the other (3 rows of pins, 17/16/17 - DB50?). I'm guessing >> this will be a huge score to someone, just not sure what it goes >> with. :) > >I'm not sure how fair it is to call a DD50 "Qbus", since Qbus is a >card-edge connector bus. > The Qbus sockets on the back of my Vax 4000-100A are DD50 so I guess DD50 connectors are used on Qbus cables for at least some applications? > >>But this might be a SCSI cable; I've seen both DB25 and DD50 used for >>SCSI (D-shell SCSI in my experience always uses male connectors on the >>cables, but my experience with DD50 SCSI is pretty much limited to >>Suns). It might be useful to buzz it out.... >> > It sounds to me like a V.24 adapter cable for something like a DEMSA X.25 router and various other DEC synchronous serial items. This would seem to be a BC19D-02 from what I can find. Is there a part number stamped on it? See http://www.islandco.com/cables.html#bc19d Regards, Peter.

15 years, 10 months

Dumping MCM6832 PROMs

by derschjo＠mail.msu.edu

Anyone out there have the capability to dump Motorola 6832 PROMs? I'd like to dump the rom sets from my Tek 4051 (and expansion packs) for some reverse-engineering but I don't currently have any means to do it. (Can't use the Tek to do it since the system software is BASIC only and has no low-level memory access functionality.) Ultimately I'd like to be able to build a custom expansion ROM pack with my own code on it, and eventually write a 4051 emulation. (And of course if anyone out there's already dumped this stuff, I'd love to get a copy...) Thanks, Josh

15 years, 10 months

Powering up a 20-year old MicroVAX II

by RodSmallwood＠mail.ediconsulting.co.uk

They can often go down internally without the top going. Some have vents that end up next to the PCB. I did four years in a high voltage test lab. And..... Yes they do pop and they can explode! Rod Smallwood -----Original Message----- From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org] On Behalf Of Gordon JC Pearce Sent: 23 February 2009 10:25 To: On-Topic and Off-Topic Posts Subject: Re: Powering up a 20-year old MicroVAX II Rod Smallwood wrote: > Hi > Sounds like capacitors. > Alhough it's a switcher any high voltage/high value capacitors in the > PSU might well need reforming. > Quite often you will see caps with a pair if incised lines on top. > This makes them go pop instead of bang. > You would not want to see a PSU where they have gone bang. This is the only popped electrolytic I have ever seen, in damn near 30 years of fiddling with electronic stuff: http://www.gjcp.net/~gordonjcp/blowncap.jpg Gordon

15 years, 10 months

Can someone help me identify this IBM machine?

by mwichary＠gmail.com

I spent 20 minutes on Google without much luck: http://www.flickr.com/photos/mwichary/3300685689/ It seems like a calculator. Thanks in advance! -- Marcin Wichary Sr. user experience designer, Google Graphical User Interface gallery >> www.guidebookgallery.org

15 years, 10 months

Electrolytics

by tshoppa＠wmata.com

>>> I have to say, for all the talk of failing caps in power supplies >>> I've only ever seen one electrolytic cap fail *ever*, and that was >>> last week in a one-year-old graphics card that has hardly ever been >>> powered off... >> >> > Gordon, you don't mention how many caps you've looked at or tested, or > how you've done so, but I encounter them constantly. Not so much in > the 1980's vintage DEC equipment YET, but it's no myth that AEC's are > electrochemical vats that have a lifespan. The lifespan varies widely > depending on many factors, heat being the big one. My gut feeling is that electrolytics got a lot lot better in the 70's compared to earlier generations. It's not just that they're 20 years newer than the ones from the 50's, they really were better quality to begin with. I work on old radios and it's pretty much a given that any set has electrolytics in need of replacement. If the set was used for a while, in fact some lytics were probably already replaced in the 50's or 60's, and maybe the replacement needs replacement today. "Failed" is a relative term... it's easy to find electrolytics leaky enough that they no longer meet their original spec, or leaky enough that they get warm. But the set still works. Other times they literally explode, or they cause other components in the circle to fail catastrophically... my experience is that switching supplies are far more sensitive to out of spec ESR's in electrolytics than any old radio ever was. Tim.

15 years, 10 months

servicing terminals/monitors

by slawmaster＠gmail.com

I've got a quick question about power safety here. My ADM-3A has needed fiddling for a while, since what I believe is the flyback is making a very high-pitched whine that gives me a splitting headache and makes it hard to see straight after 5 minutes. I want to take a poke around, make sure everything is connected firmly, make sure none of the components are visibly bad, that kind of thing. How long does it take an unplugged CRT to discharge? This hasn't been plugged in for over a month, so I figure it's probably safe right now, but if I test it and then want to check something else, how long do I need to leave it sit? Is there a safe way to discharge a CRT when you're working on it in the living room? I'm a little leery of just shorting connections with a screwdriver randomly, although that's almost exactly what I did the first time I worked with a CRT :) (it was 5th grade, and I had just had it on, unplugged it, opened it, and started poking around with wires. BIG SNAP) Thanks John -- "I've tried programming Ruby on Rails, following TechCrunch in my RSS reader, and drinking absinthe. It doesn't work. I'm going back to C, Hunter S. Thompson, and cheap whiskey." -- Ted Dziuba

15 years, 10 months

Powering up a 20-year old MicroVAX II

by js＠cimmeri.com

-----Original Message----- > From: cctalk-bounces at classiccmp.org [mailto:cctalk- > bounces at classiccmp.org] On Behalf Of Robert Jarratt > Sent: 20 February 2009 22:45 > To: cctalk at classiccmp.org > Subject: Powering up a 20-year old MicroVAX II > > I have just collected a MicroVAX II which has been in storage and has > not > been powered on for 20 years. This is my first machine of such an age, > unfortunately I am not particularly knowledgeable at the electronics > level > (I studied circuits academically 25+ years ago and can solder a bit, > but > that is as far as it goes). I know I will need to treat it carefully in > order to get it working again. I plan to open it up and make sure I > clear > out any debris etc, but beyond that I need advice from those with the > experience and knowledge that I lack on how to go about powering it up > carefully. > Thanks Rob > After removing all the boards and leaving just the disk and tape drive for load I impetuously decided to try powering it up. I knew the PSU (model H7864) was set for 110V and made the switch to 240V (I am in the UK). When I connected the power cord, after a few moments there was a loud pop, followed by another before I could pull out the power cord, smoke rose from the PSU. This sounded just like when I had once accidentally made a 110/240 mix-up. The question is, could it be that I had not made the switch to 240 correctly, or could this just be down to the age of the PSU? ---- *Rob, possibly you made the 110/240 switch wrong, but also possible is that the PSU just wasn't ready to be turned on like that. Electrolytic Capacitors (of which there are many in that PSU) tend towards non-functionality the longer they sit unused. Without those caps working right, the PSU will do pops, smokes, and other alarming things. Then good luck fixing it. What I do with an old PSU like that is test each cap prior to it ever being powered up.. both for capacitance and ESR. Usually, some or all of the caps need reforming or even replacement. Only after the caps are back to health, do I then give the PSU power... at first with the smallest load I can get away with. If it's a switcher PSU (as that one is), I'll bring it up quickly to about 90V using a variac... then in 5V increments every 1/2 hr after that to 130V, then back down to 120V. This in the USA. jS *

15 years, 10 months

TransEra documentation

by aek＠bitsavers.org

Going through my Tek 405x stuff, I realized I hadn't uploaded anything >from TransEra, who was a third party supplier of firmware. http://bitsavers.org/pdf/transEra

15 years, 10 months

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test-drb February 2009