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Digital Group Z80

Thanks Marty... I think I agree. Although I'm surprised the OS wouldn't fit into the base system RAM config. IIRC the manual calls on you to load it with just the three boards. Anyway, I'm going to keep testing RAMs the only way I can for the moment. As it turned out, there were some bum RAMs on the CPU board, if my testing regime is correct. I started taking RAMs off the CPU board, putting them on video and then putting 'known good' back into the CPU.. three 2102s off the CPU board generated bad video.. so I guess they were not good. For kicks, I tried loading the OS again. It breaks down at exactly the same place, however this time instead of stopping before it hits 7s, it clears the screen and dumps a whole bunch of random characters and continues to as the tape runs.

Anyway, with the jumper settings better understood now I'm aiming to get enough known good 2102s to fire up 'BD 0' (as the previous owner labelled it) up.. we'll shoot for a 10K system (I guess that's what it is.. 2K+8K), and then if that works, see if we can work our way to an 18K. The third board obviously will be impossible unless I acquire more 2102s.
 
Hi All;

Falter, I don't remember whether the lower addressed Rams start at the top of the 8K memory Board or at the bottom of the Board..
But, until You find out different pull the Rams from that Last Board from the bottom Row if 2102's and work You way to the top of the Board..
Hopefully, that way You would have at least a Partial last Board to work with.. You might not have 18K, but anything would be better than 10K..
Good Luck on the Ram Testing, and congratulations on getting it going..

THANK YOU Marty
 
Thanks so much Marty.. I appreciate all your help very much!

Good news!

After much fidgeting and testing to get a complete good RAM board, I rejumpered the CPU board and was able to load Z80 OP SYS! Woohoo! I'd take a picture but unfortunately my phone ran out of batteries.

Now for the next problem. The keyboard does zero. I tried all four keys with no success. Any key really.

So tonight I'll read through the docs. I'm suspecting possibly I have the keyboard PCB plugged into the wrong port, or something's up with the IO card. The fellow who rigged up this keyboard installed LED lights, and if I understand how he's got it, when you hit a key, it lights up certain lights numbered 0-6, or combinations thereof (binary?). It consistently lights up certain lights with certain keypresses. There is also a light marked 'strobe' that flashes every time you hit a key.

So I'm thinking the issue isn't with the keyboard or the decoder he made for it..
 
falter said:
Good news!

After much fidgeting and testing to get a complete good RAM board, I rejumpered the CPU board and was able to load Z80 OP SYS! Woohoo!
Click to expand...

Excellent! Good for you! I'm on the sideline here, rooting for you all the way.

falter said:
Now for the next problem. The keyboard does zero. I tried all four keys with no success. Any key really.
Click to expand...

Too bad about that. But, with the system working, at least you now have another tool to help you with making further tests and seeing what the results are.

Go man go!

8-)

smp
 
Hi All;

Falter, Good News on the Memory front..

On the Keyboard issue, the same Port that does the Video, does the Keyboard, if He left it Standard Digital Group..

A couple of things to try, first turn the Keyboard Paddle card around and try it.. and If that Doesn't work, try the other slot in Both Directions.. The Keyboard is Input Port 0.. On the I/O Board on the Component side check where pins 1 thru 8 are wired to, as well as IC 1 and IC 2 (7401's)..

Like I said in a previous post, follow the wires..

THANK YOU Marty
 
Thanks guys. Pretty exciting to see this thing operate.

Marty: I'll try different ports.. there are three.. only two seem to have wires. I had debated trying or flipping the keyboard pcb over but I was afraid of shorting something if it was wrong.

I'm trying to figure out how old this thing is. The fellow that runs Byte Collector says this 'Basic Box' setup was offered later in production.. but 95% of the ICs date from 75 or 76. Two power supply components date from 76.. one dates from 78. My understanding is that Digital Group had trouble maintaining reliable inventory.. they wouldn't have had chips etc sitting around for a couple years before use would they? I'm wondering if parts of this machie might have been built over time, the case coming later.

Marty said:
Hi All;

Falter, Good News on the Memory front..

On the Keyboard issue, the same Port that does the Video, does the Keyboard, if He left it Standard Digital Group..

A couple of things to try, first turn the Keyboard Paddle card around and try it.. and If that Doesn't work, try the other slot in Both Directions.. The Keyboard is Input Port 0.. On the I/O Board on the Component side check where pins 1 thru 8 are wired to, as well as IC 1 and IC 2 (7401's)..

Like I said in a previous post, follow the wires..

THANK YOU Marty
Click to expand...
 
Even if they kept no inventory, it wouldn't be unusual to buy chips dated 1976 in 1978.
 
Okay, as usual Marty was right. The keyboard was in the wrong port. I moved it to the lowest port and voila.. works like a charm.

I tried loading MAXI BASIC and even TINY BASIC but couldn't quite pull it off. TINY BASIC says '10K' on the tape, and I've noticed again as it goes through the numbered page loading it gets spotty after a while. The OS, which just requires getting through 8 'pages' (I guess that's what the 0-7s are), but the others require multiples of that.. around the second or third run starting at 0s again, the system starts spitting out periods which in past experience means out of memory. So I guess I will dedicate some time today to getting a second board running and hope that'll do it, because that's all I've got until I get some more 2102s to replace the dead ones on the third board.

Once I get the memory situation sorted, I'm not sure how to approach these game tapes like QUEST III, etc. Would I try to read those direct off the OS? Or load and run from within BASIC? I'm assuming there wouldn't be too many non-BASIC games out there for these things.

I'll put a video up as soon as I get my camera to display monitor text properly. I might even hook up my VM4509 for the appropriate retro feel. The Commodore monitor isn't cutting it. What a neat 'little' machine.
 
falter said:
Okay, as usual Marty was right. The keyboard was in the wrong port. I moved it to the lowest port and voila.. works like a charm.
Click to expand...

Yay! That's great. Now on to the real work of getting the system into some sort of useful shape. ;-)

falter said:
I tried loading MAXI BASIC and even TINY BASIC but couldn't quite pull it off. TINY BASIC says '10K' on the tape, and I've noticed again as it goes through the numbered page loading it gets spotty after a while. The OS, which just requires getting through 8 'pages' (I guess that's what the 0-7s are), but the others require multiples of that.. around the second or third run starting at 0s again, the system starts spitting out periods which in past experience means out of memory. So I guess I will dedicate some time today to getting a second board running and hope that'll do it, because that's all I've got until I get some more 2102s to replace the dead ones on the third board.
Click to expand...

Wow. 10K doesn't sound so "tiny" to me. But, you might as well take whatever clues you have, at this point.

Cassette loading is going to be touchy. You're probably in for lots of playing around with the volume level, in order to find what is the optimal setting to get a load to go properly. Even then, you may have some variability from time to time. If you're lucky, you won't have to find the optimum for each and every tape...

You might want to consider making your own copies. Maybe tape at first, but consider going to some digital medium. Much more consistent, and it'll last a much longer time than those old tapes will, for sure.

I'm having a blast watching your progress. Thanks for sharing.

smp
 
Hi All;

Falter, Great News !!
I kind of figured that it would not be too much to getting the Keyboard going..
I can't help You with 'The Games' as I never played the Games, to me it was a waste of time..
I have a multiple of Tapes, which I need to find out or figure out How to Transfer to You..
One of which I call Copy HI, which is an exact copy of the Operating System, except that It reloads whatever you are loading in at page 11, instead of at page 01..
So You can load something in like the origional Operating system at page 11 and then look at it to either modify it and resave it to another cassette or to print it out for study..
I also have another Operating System Called ICOSE, which was written for the 8080 Processor Board and it had an Editor , Assembler, and a Tracer utility, in very Low amount of Memory.. And Worked Great, You could Write or change Your own Mnemonics for the Assembler.. Pages 01 thru Page 027..
It would not fully work on the Z-80 and I have it fully written out on Paper, But I could not quite figure out, how to make it work on the Z-80, it mainly was the Timing difference between the two boards.. The 8080 ran at 2.00 MegaHertz and the Z-80 ran at 2.50 Megahertz..
I'LL see what I have left in Tapes and let You know..
Ok, what I have left is DG Assembler, (I don't know if it is Assembler I or Assembler II), DG Dis-assembler, Proms, Software Proms, Convers..
Various DG programs, PT Basic, all which came off of the origional Icose Tape.. Copy HI, Copy HI with Clear Memory.. Z80 system with Icose Assembler.. (I don't know if this is working or not.. Icose #68 and Icose #73.. Mostly a change of Assembler Mnemonics..
And Icose #80 which is for the Digital Group Single Density Disk Controller, but it is not complete..
From there It went to an S-100 SpaceByte 8085, with 8" Floppy Controller Double Density, (which I have the same System) and Now it's running on a PC and being used by it's creator who is a Software Engineer for Writing and Maintaining current Software at the Company where He Works..
So, a variant of the Icose Software is still Running today..
Basically, with Icose, you had Letters for telling the operating system what You wanted.. Like As for Assembler, Wr for Write, Ed for Editor, etc..
Also, Your Tape loading , Might need a little tweaking, but for Now untill it shows a problem, I would leave it alone..
THANK YOU Marty
 
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Yeah I kind of thought the whole point of 'Tiny' BASIC was, you know, what its name implied. I think 10K seems a bit heavy. I definitely think I'm running out of RAM, it loads to a partially corrupted menu, and does the .... thing between digits as the pages load. So I think a bit more RAM and we can at least get that going.

I've posted a video of the unit firing up just for those who encounter this thread later and want to see one of these in action:

https://www.youtube.com/watch?v=fm9aPOjvBt0

I think the tape drive is working perfectly. What I need to do now is try and isolate which 7401 was giving me hassles before (I need the NOS 1973 7401s I used back for my TVT project).

Later tonight I'll do some more RAM testing and get that second RAM board functioning if I have enough 2102s to pull it off. Then hopefully I can do some BASIC programming.

I'm really glad I bought this thing. The earliness and hobbyist nature of it makes it special, I think. Even the 'font' it uses is kind of cool. The fact that it required, really, only minimal work to get it going again is impressive, when you consider it's going on 40 years old! I kind of wonder what it's original builder would think of the fact that a then 1 year old would be using it today in 2016.

Of course, it's never enough. Now I want to go down the rabbit hole of the DG Phi-deck. If one of those ever comes up... :)
 
Hi All;

Falter, Depending of How much/many 2102's You took out of that last Board, and from What I can Gather from Your postings, That You should have about 6 to 7K left on that Last Board.. Which Should get You Enough Ram To Load the Operating System and the Memory Test, Which might be of some Help to You..

"" Of course, it's never enough. Now I want to go down the rabbit hole of the DG Phi-deck. If one of those ever comes up... ""

Actually, I have The DG Phi Deck, I have Never had it going as I think it Should be.. There could be Many Reasons, I think it was Noise and Old Tape Heads.. It would drop Bits, Or at least not Load Correctly..
My Plan was that after, I got You Going, I was going to Sell Everything or Almost Everything, Including the Phi-Deck Stuff..

I Just Don't have any Idea What it is Worth, I Don't Want to Cheat You, Nor Cheat myself..
I know where the Boards are and the Case, But, I would need to find the Phi Deck Cabinets and the Decks Themselves..
And I have Two kind of Decks, one for the Digital Group and Another for my S-100 Alpha-Meca System, which isn't working either, possibly for the same Reasons..
I would need an Email from You to Send You Pictures of what all there is..

THANK YOU Marty
 
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So I don't have to fully populate a memory board to use it?

Marty said:
Hi All;

Falter, Depending of How much/many 2102's You took out of that last Board, and from What I can Gather from Your postings, That You should have about 6 to 7K left on that Last Board.. Which Should get You Enough Ram To Load the Operating System and the Memory Test, Which might be of some Help to You..

"" Of course, it's never enough. Now I want to go down the rabbit hole of the DG Phi-deck. If one of those ever comes up... ""
Actually, I have The DG Phi Deck, I have Never had it going as I think it Should be.. There could be Many Reasons, I think it was Noise and Old Tape Heads..
My Plan was that after, I got You Going, I was going to Sell Everything or Almost Everything..
I Just Don't have any Idea What it is Worth, I Don't Want to Cheat You, Nor Cheat myself..
I know where the Boards are and the Case, But, I would need to find the Phi Deck Cabinets and the Decks Themselves..
And I have Two kind of Decks, one for the Digital Group and Another for my S-100 Alpha-Meca System, which isn't working either, possibly for the same Reasons..
I would need an Email from You to Send You Pictures of what all there is..

THANK YOU Marty
Click to expand...
 
Hi All;

Falter, "" So I don't have to fully populate a memory board to use it? ""

NO !!!!!!!! Just make sure that each side row has 8 Rams in there, if there are less than 8 take that row out, and save the Rams someplace until You can get more..

Here is a Sample of What is Possible with a Digital Group Cassette System..
It is the Listing for the Tracer Program from Icose, It is a free flowing Assembler that He Uses..
And of course You most likely won't Recognize the Assembler Mnemonics..

001.jpg 002.jpg


003.jpg 004.jpg 005.jpg


THANK YOU Marty
 
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So I tried adding in the second RAM board, but what I get is a field of all the same characters. I checked all the 2102s in my video board and they all checked okay. I triple checked the jumpers.. I have the CPU card jumpered for 16-18k, and I checked to make sure this board is jumpered for 8K-16K.

I tried changing some of the other chips.. the 7404s and 7424, eventually swapping the entire set from my last board.. in swapping 7404s I got the characters to change (just to a full screen of a different character).. but that's it. Bad logic? Maybe I'll try swapping them one at a time with my good memory board and see what's going on. I note, the system will function even though the CPU is jumpered for two boards, with only one board in.
 
Hi All;

Falter, "" I note, the system will function even though the CPU is jumpered for two boards, with only one board in. ""

Sure , but it will only see 8K and then an 8K of nothing and then 2K of memory..

Look for not only bad logic on the Second 8K Memory Board, but a possible short, trace short or something like that..
Especially, if something has been dragged across the Board..

If You are still not sure Take Everything out of (from) the the Board, both IC's and Rams and then plug it in..
If it then jams up the system, You have a Board short..

THANK YOU Marty
 
Thanks Marty. I've ruled out the logic chips.. tried them all in the working board.. no problem. Interestingly.. if I switched 7404s around sometimes I got a different pattern, like this:

20160325_222938.jpg

I did kind of look around the board.. visually looks ok.. but I'll try what you suggested tomorrow. Thanks again!
 
Hi All;

Falter, "" the 7404s and 7424, "" I hope that, is a typing Mistake, and Not what is really there.. I think it should be a 7442..
But, Just in case Check that what Ic's are in one Board are the same and in the same place on both Boards..
"" if I switched 7404s around sometimes I got a different pattern, ""
That then would be my other place to check, Possibly a Bad 7404..
Also, check family type, I would say Plain or LS, and not anything else..
I would check the Data Driver, a 74125 or an 8T97/74367, I don't Remember which it has at the Present..
Otherwise for Now, 10K of Memory would be fine..
I Don't have any 8K Boards, So I can't Help You in that way..

THANK YOU Marty
 
Sorry it was 7442.

I did some experimenting. I'm not sure if this helps the cause, but after pulling all the RAMs on the left side of the second memory board, I plugged it in (with the right bank remaining). The machine came up okay. I tried loading TINY BASIC just for fun (I'm not sure how to tell how much RAM the computer actually sees). It loads better, but again somewhere around the third round of '5s' it throws a bunch of periods in.. then solid 6s.. then it brings up the Tiny BASIC menu but the video is corrupted. It does that every time at the exact same place. I tried a simple loop program (even with the prompt being forced out into the middle of the screen) but nothing runs. Maybe TINY BASIC isn't as simple as the BASICs I'm used to. Or there's corruption happening in the load process.

Anyway, I started re-adding RAMs line by line to the board and powering up to test. The first three rows of 8 on the left side = no problem. As soon as I add the last row on the bottom left side (IC 70-77), that's when it hangs. I did a look around at the soldering and traces but I don't see any shorts, etc. Can the board still be accessed with that one line out? I know you mentioned the boards could work with some rows out, but I wasn't sure if certain rows (like the bottom or top) were special in some way.
 
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Here's the attempt to load Tiny BASIC. Fails in the exact same spot. Maxi BASIC does the same thing. They will both function to some degree after they finish.. but.. not sure if its some bad ram I missed somewhere, maybe bad tape.. two of the tapes I tried snapped on me. They are pretty old..

https://youtu.be/O_86jYaKIgw
 
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