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Digital Group Z80

falter

falter

Veteran Member
Joined
Jan 22, 2011
Messages
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Location
Vancouver, BC
I was feeling kinda bummed about missing those early Rev Apple II boards. I skipped the Rev 1 to conserve funds for the Rev 0, but missed the Rev 0 by just a few bucks because I didn't bother to up my bid enough. Oh well.

However I came across this in the dying minutes of its auction:

http://www.ebay.com/itm/Z80-Compute...ry-rare-computer-from-the-1970s-/371549849675

To be honest, I'm not a big Z80 fan. I don't know why - apart from a few pieces like my ZX80, etc.. I've always kind of seen the Z80 as the Toyota Camry of CPUs. But this piece, allegedly, is the very first computer designed around the Z80, and I know Digital Group was popular back in the day, though it failed because of supply problems. I actually only noticed the keyboard first, which I believe is the same unit used by some of the orignial Apple I builders. My collection, which has about 100 pieces thus far has been kind of scattergun, but I've begun lately to focus on rarer/unusual/homebrew stuff. This seemed to fit the bill.

Anyway, I threw in the minimum bid and got it unopposed. Which means either I overpaid, or just fluked out. I was sure I wouldn't get it -- so used to bid snipers, but they didn't appear. Personally I don't think I overpaid if the history is correct and this is what it purports to be. I like that it even has some software thrown in with it, if those cassettes are correct and still good. I don't know.. I think $695 was a decent price.. what do you think? Is its claim to being the first Z80 computer true?
 
Very interesting.

But I think you overpaid. My guess is that it doesn't work and you'll have a hard time getting it working.
 
Yeah it was kind of a quick call on my part. I've been neck deep in vintage ICs, so I'm confident there's value there, though I wouldn't dream of tearing that machine apart. And the keyboard, I'm sure I've seen a few of those go to Apple I replicators for considerable dollars. The CPU is August 1976, not long after introduction, so that's kind of cool -- I think the ceramic Z80s command $150ish. It's something I've never seen before and I don't think many other people will have. I want to try and get more oddball stuff that isn't so hot with collectors and that there won't be three or four of at a vintage festival. It may not work, but, one by one I have been slowly getting my non-working stuff working. I like that it's from the 'early' era, from a now defunct company and that it came with actual software. Only thing that sucks is our CDN$ being in the toilet. That makes it hurt a little.
 
Neat! I've read about the Digital Group bus in "The S-100 & Other Micro Buses" -- seems simple enough. I don't know if you can find schematics for the boards that came with the system, but it shouldn't be *too* difficult to get going. With the bus definition and a bit of protoboard, you could build yourself a debug board and see if it has any life in it.
 
Regarding price, I think you probably did fine. It doesn't seem like you can get a complete system from that era for less than $500 nowadays, unless you just get really lucky on it. I guess the fact that it's not an Altair, IMSAI, Apple 2, PDP, or one of the other "big names" with vintage computer hobbyists makes it "less valuable" to some, but I'm with you on being more interested in systems that are homebrew or modified into something unique.
 
Yeah. I think, from what I've read, that this is a pretty early example -- the later units apparently had a more professional case and it looks like a standardized keyboard. I think it's kind of a cool thing even if it doesn't fire up. It'll fit right in beside my SWTPC stuff. I'm really holding out for a 6800 system but for some reason there hasn't been one on ebay in months.

I mean, I'd love to have an Altair, but I'm increasingly less interested in competing with moneyed Baby Boomers for that kind of thing. I'm of two minds, one is get it now before it's unattainable, the other is I'm suspecting there will be fewer and fewer vintage computer collectors as the generations that remembered and used this stuff pass on, maybe it'll be going for a slight discount down the road.

The only thing I'm a bit concerned about is the tape storage system. It looks like they had their own proprietary tape devices (I've seen a four-plex kinda unit in pictures) -- I'm wondering if it also used a standard tape deck and/or if I'll be able to rig something up. Be a pity if I get it working but cannot use those tapes.
 
falter said:
I mean, I'd love to have an Altair, but I'm increasingly less interested in competing with moneyed Baby Boomers for that kind of thing. I'm of two minds, one is get it now before it's unattainable, the other is I'm suspecting there will be fewer and fewer vintage computer collectors as the generations that remembered and used this stuff pass on, maybe it'll be going for a slight discount down the road.
Click to expand...

The same thing has happened with early cars, I suspect it will happen with some (maybe not all) vintage computers. I could see Apple 1s and rev 0 Altairs holding their value.

To me, it's just more interesting to see the different approaches engineers, hobbyists, and companies were taking in trying to figure out the next thing with computers. That's part of why I like hacking on my Ohio Scientific system! I suspect this machine will offer you a similar experience -- from what I've read, the Digital Group bus was meant to be generic enough to work with any of the popular microprocessors of the time (8080, Z80, 6800, 6502, so it says in "The S-100 & Other Micro Buses").

BTW, the system you purchased is pictured in "The S-100 & Other Micro Buses" as, "An open system by The Digital Group!" It appears that the entire card cage is hinged, and swings up and out to the left on the unit (as seen from the front). This lets you get to the pins on the 72-pin I/O bus, which by default aren't connected to anything and are available for connection to external devices (or each other, for multi-board sets).
 
falter said:
Anyway, I threw in the minimum bid and got it unopposed. Which means either I overpaid, or just fluked out. I was sure I wouldn't get it -- so used to bid snipers, but they didn't appear. Personally I don't think I overpaid if the history is correct and this is what it purports to be. I like that it even has some software thrown in with it, if those cassettes are correct and still good. I don't know.. I think $695 was a decent price.. what do you think? Is its claim to being the first Z80 computer true?
Click to expand...

I think it's on the high end price wise for what was there. The keyboard is fairly common, and is from a TI Silent 700. The big and expensive part missing are the PHI-decks for the cassettes. As a collectable, a DG system in the tan aluminum case with matching cassettes, and Keytronic keyboard would be much more valuable.
I see what you got as a parts source for one of those.
 
I'm curious -- given they were just starting out when these Z80 machines were developed, and given they were sold initially as a hobbyist kind of thing, would they not have offered some method to use readily available tape decks?

I'm reading the documentation I've found and it looks like there were two cassette interfaces possible -- the PHI-deck (with its own card), and a cassette interface built into the 32 or 64 character video card. I've seen some pictures of the motherboard with what looks like standard 'In' and 'Out' jacks (I think they're jacks, or solder points).
 
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falter said:
Answered my own question. Per this document here: http://bytecollector.com/archive/digital_group/documentation/hardware/dg_systems/dg_systems.PDF

You initially built the system to use an off the shelf tape recorder. They said anything from a $20 'el cheapo' to more expensive units would work. Phew. Now, I wonder how those tapes are formatted..
Click to expand...


Tapes are not formatted at all. Usually you'd take ordinary music tapes, rewind them and push "record" to record your data. To load your data you rewind them again and press "play". Pretty much like recording music, just that it's data from a computer, sound a bit like when an old modem is transmitting data.
 
Kansas City Standard will get you off to a good start. When I started out with my Altair, I took the guts from an old Novation audio modem and added a few components so it could do both originate and answer tone signalling. With a cheap GE portable tape recorder, I had my storage, albeit at 300 bps.

There were, to be sure, purely digital encoded tapes and drives, some using 2 tracks (one for clock, the other for data), but those were fairly expensive for hobbyists and pretty much left to the commercial world. I had a Techtran unit, but major firms such as NCR also made them.
 
Got an email reply from Bryan at the bytecollector.com site (thanks Bryan!). My Z80 system was apparently an offering called the "Basic Box", which DG offered to those who wanted a decent setup but didn't want to go full dollar on the more corporate looking brown box cases. Bryan says it's actually quite rare as most hobbyists opted to just set up in boxes of their own or at the other end just bought the brown box. It apparently came later in production after Digital Group noticed a need.

It's featured here a few pages in, in Flyer #10 for those interested: http://bytecollector.com/archive/digital_group/flyers/flyer_10.pdf

Thanks to Bryan for clearing that up. Looking forward to playing with this beast!
 
Hi All;

I just saw this Entry..
Actually, the Cassette circuitry that was used in the Digital Group was called Suding, and is Quite different than the others like Kansas City Standard, the Digital Group used what they called a software Uart, and usually loaded at 1100 Baud, Not the 300 Baud of the other Standards..
I have had a number of these machines, and I have one left, I have some Software and many Cassettes for this machine..
Also, This is NOT an S-100 machine !!!!
If I can be of any Help Please just ask..

THANK YOU Marty
 
Thanks Marty.

I got a little scared when the Phidecks were brought up. They seemed like such an exotic beast, I assumed the tapes would be recorded in a way that would not work with an ordinary tape deck. From what I've read though, all I need is, in fact, an ordinary tape deck and I think it connects into the video/cassette card somehow?

I hate to admit it but I have no idea what to buy in the way of recorders -- never had a need for one with my collection (well, had a need but never bothered to buy). Here's one I was looking at: http://www.ebay.com/itm/Vtg-Panason...508964?hash=item3d12912c24:g:f0YAAOSwDuJWzQ9t

I'm confused by the 'MONITOR' port though.. if that is the headphone jack I need. Also, I think I need mono cables?
 
Hi All;

Falter, "" I got a little scared when the Phidecks were brought up. They seemed like such an exotic beast, I assumed the tapes would be recorded in a way that would not work with an ordinary tape deck. From what I've read though, all I need is, in fact, an ordinary tape deck and I think it connects into the video/cassette card somehow? ""

Sorry, about maybe confusing You..
The regular Cassette input / output from the Video Board, used any regular Cassette Recorder.. The main thing is that it has a Stable speed, and not alot of flutter..
The PhiDecks are a beast of another option and are not used with the video Board, They have their Own Controller which plugs into the I/O slot, which then connects to the Phidecks..
They are a Real pain to get running, unless You have special Operating System Software that was third party and Digital Cassettes Tapes and have time to do modifications to both the Phideck case adding an extra circuit Board and to the Rev B or later PhiDeck Main Board, that is plugged into the I/O slot as mentioned above..
Of course You can do without the above, but then loading off of a PhiDeck would be very Hit and or Miss affair.. I never had mine working well enough to use for any kind of thing except experimenting..

"" I'm confused by the 'MONITOR' port though.. if that is the headphone jack I need. Also, I think I need mono cables? ""
I think the Monitor port is the output from the Video/cassette board that would go TO the cassette tape Recorder, Usually if the cassette Player has either a speaker or a Headphone jack then that could be considered the Monitor port.. Its purpose is to Listen to when the tape starts and ends for You to be able to turn the player on and off for loading..
"" Also, I think I need mono cables? "" The only cables You would need is for going from the Digital Group Computer to the Cassette tape machine..

I hope this Helps..

THANK YOU Marty
 
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Hi All;

Re-Reading some of the above postings, I have only a basic Enclosure (Basic box) of my Digital Group System..
I used to have the full Brown Box set up, and I had a ByteMaster as well.. Sold them Both..

Here are some picture of my Beast and an original Backplane wired for a PhiDeck.. In my basic enclosure is an Aeon MotherBoard, which had connectors added to the original Mother Board for easier connecting to other things..
This unit is quite Dirty and need some work to make it workable again, like straightening out of Pins for the I/O connector on the back, and it need a +5 volt Supply.. Hopefully, I can get to it make it workable again..

002.jpg 003.jpg

004.jpg 005.jpg

THANK YOU Marty
 
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It looks like a combination of a MULTIBUS 1 form-factor with the S100 bus. I have not counted the number of pins on the connectors to see if it is MULTIBUS 1 however...

Dave
 
Hi All;

Dave, good to hear from You again. I had sent You a private message, awhile ago and I got no answer back from You..

It is Not MULTIBUS, But, what Dr. Suding Dreamed up..
The Processor Board is 100 pins, The memory is something like 72 pins, the video / Cassette card is 44 pins, the I/o is 44 pins on the computer input side and on the side to other things is also 72 pins..

THANK YOU Marty
 
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