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Coleco ADAM RAM Expansion options - Advice please


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#51 CharlesMouse OFFLINE  

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Posted Mon May 6, 2019 5:46 AM

Is there a technical manual available for the Adam?

Yes there is, I can't place the link at the mo' but I'll post it when I remember.

 

 

Grrr, I think I'm getting silly now:

-A15 line, doh! Reinstated (That will be another patch wire for my current board - I wonder if that will fix the funny RAM report in File Manager 3.0?)

-B0-B2 whacked on to A16-A18...

...what about B3?

 

-Bah! Lets add another 4mb RAM IC (nuts)

-B2 swapped for B3 on the second IC...

...I think I'm getting a bit dirty now. I guess that will work but I've applied no brain cells to the iteration - thoughts?

 

So... having proven to everyone that at best I don't properly sanity check my designs properly and at worst I am clueless what do you say to an 8mb RAM board for the ADAM?

(assuming I haven't done anything else truly stupid)

Attached Thumbnails

  • ADAM_Mem_8mb_v1_sch.png

Edited by CharlesMouse, Mon May 6, 2019 5:49 AM.


#52 ChildOfCv OFFLINE  

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Posted Mon May 6, 2019 11:17 AM

That would have both chips responding to all addresses, except that when B2 or B3 is active they will respond differently.  Unfortunately, the extra logic needs to be on the chip select lines, with both chips using B0-B2 in the same address scheme.

 

The CAS lines need an OR gate for each line.  CS on one chip will be CAS | B3, while CS on the other will be CAS | NOT B3.  On the good side, you do have a few NOT gates left to play with.  On the bad side, though, you need to add an OR gate.


Edited by ChildOfCv, Mon May 6, 2019 11:18 AM.


#53 CharlesMouse OFFLINE  

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Posted Mon May 6, 2019 1:41 PM

Thank you you once again. A, hopefully, better attempt shortly

 

A general question:

This new 'design' is the result of boredom and a sleepless night making me wonder if I could make a smaller board with fewer IC's. Then having B3 dangling urged me to add another RAM chip...

-1mb already silly?

-If the cost of a smaller board is more RAM that's fine

-8mb is stupendously pointless

-Now you've gotten this far just do it and nuts to the pointlessness.

 

...if only Hex NOR gate ICs were a thing. Not quite enough logic to use a 7402 in place of the 7404.


Edited by CharlesMouse, Mon May 6, 2019 2:24 PM.


#54 HDTV1080P OFFLINE  

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Posted Mon May 6, 2019 3:19 PM

I would be interested in 16MB, 32MB, 256MB or larger memory expander for the ADAM computer. A talented programmer could use the extra memory instead of using it as a copy buffer. A new version of File Manager could be created so a 256MB copy buffer could be used.

 

I have been told that File Manager (and maybe some other programs) does work with 2MB memory expanders. Right now I only have a 1MB memory expander, but if I had at least a 2MB memory expander then that would be ideal for me to copy my 1.44MB disk images and use the 2MB memory expander as a copy buffer. Those that own hard drives for the ADAM comptuer could use a 256MB memory expnader as one big copy buffer.

 

If you start making home brew memory expanders at 2MB and above my interest in this project well greatly increase since I may want to solder my own 2MB to 256MB memory expander to use in my ADAM computers.


Edited by HDTV1080P, Mon May 6, 2019 3:21 PM.


#55 CharlesMouse OFFLINE  

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Posted Mon May 6, 2019 3:29 PM

@HDTV1080P:

I sincerely hope I'm homing in on a working 8mb design and if so and you find it useful I'll be most pleased indeed.

 

I also hope I haven't made any further stupid mistakes, I really have made a meal of this one. Many thanks to everyone, especially ChildOfCv for your most helpful pointers and patience.

 

Fingers thoroughly crossed!

Attached Thumbnails

  • ADAM_Mem_8mb_v2_sch.png
  • ADAM_Mem_8mb_v2_brd.png

Edited by CharlesMouse, Mon May 6, 2019 3:35 PM.


#56 HDTV1080P OFFLINE  

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Posted Mon May 6, 2019 3:42 PM

If you do get a printed circuit board printed up and solder 8MB of memory on it. Let me know what File Manager sees. Awhile ago when I was playing around with a memory expander with 64MB installed, I thought File Manager mentioned 16MB of memory.

 

See this post where I tried to install 64MB of memory on a existing 1MB memory expander and it would not fit in the ADAM computer. Your doing the correct time consuming method of designing the circuit board from scratch.

 

http://atariage.com/...ufff/?p=4182084


Edited by HDTV1080P, Mon May 6, 2019 3:43 PM.


#57 HDTV1080P OFFLINE  

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Posted Mon May 6, 2019 3:53 PM

The ideal thing to do for the ADAM memory expander is to modify a solid state drive so that it works in the ADAM as a memory expander out of slot number 3.

 

Or make a ADAM memory expander that has a full size SDXC card slot so one could plug in a 64GB SDXC card into the memory expander. Then when the power goes off the 64GB SDXC card would still maintain its memory.

Of course that would be a lot more work in both hardware and software programming.


Edited by HDTV1080P, Mon May 6, 2019 3:54 PM.


#58 CharlesMouse OFFLINE  

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Posted Mon May 6, 2019 4:43 PM

It's funny. Now that I think about it your adventures with memory is a large part of what got me to jump down this rabbit hole.

 

Yes, I could see the merits of a SDXC- based solution but at least for now that's going to be biting off more than I can chew. An old-school option would be battery-backed RAM.

 

Now I've got what little brain I have in gear (with much help!) I think I'm closer with this board. I was more than chuffed with the 1mb version but wanted to see if I could do something neater and the extra RAM sort-of arrived for free.


Edited by CharlesMouse, Mon May 6, 2019 4:44 PM.


#59 HDTV1080P OFFLINE  

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Posted Mon May 6, 2019 4:56 PM

I would be interested in a battery on the memory expander so that it holds its memory when the power is turned off. However a jumper would need to be a option for those people that want to bypass the battery and prefer the memory expander to lose its memory when the ADAM computer is turned off. 


Edited by HDTV1080P, Mon May 6, 2019 4:58 PM.


#60 CharlesMouse OFFLINE  

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Posted Mon May 6, 2019 7:33 PM

I would be interested in a battery on the memory expander so that it holds its memory when the power is turned off. However a jumper would need to be a option for those people that want to bypass the battery and prefer the memory expander to lose its memory when the ADAM computer is turned off. 

 

Done, and done. :-)

 

Battery backup could be a very nice thing to have, a non-volatile RAM disk being something I'd quite like - of course I've no idea if there's any software available that could cope with such a thing. It's probably obvious I can barely make a PCB, coding is quite beyond me.

Can you spot the spelling mistake(s)..? I really must get some sleep.

 

 

...I just hope the general consensus is the pesky thing will work and I'll go make another order with Seeed.

Attached Thumbnails

  • ADAM_Mem_8mb_v2_BAT_sch.png

Edited by CharlesMouse, Mon May 6, 2019 7:40 PM.


#61 ChildOfCv OFFLINE  

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Posted Tue May 7, 2019 3:34 AM

Just wondering, what is Seeeeeeeeed's turnaround time?  I've ordered a few times from Osh Park and typically it's a couple of weeks before it arrives.  Would be nice to find a faster source.



#62 CharlesMouse OFFLINE  

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Posted Tue May 7, 2019 5:06 AM

Just wondering, what is Seeeeeeeeed's turnaround time?  I've ordered a few times from Osh Park and typically it's a couple of weeks before it arrives.  Would be nice to find a faster source.

 

It's about the same, sometimes a bit quicker, sometimes slower... it seems to be mostly about the postage with them - when I put in an order their updates suggest the PCB fabrication is done in about 2-5 days. They do have options for fast delivery but I'm too cheap to have tried that.

 

 

Forgive my paranoia, I'm about to send this design off to Seeeeeeeeed (:-)) but I've made so many mistakes with this project confidence is low. Do you think the latest design looks reasonably sound?



#63 ChildOfCv OFFLINE  

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Posted Tue May 7, 2019 11:18 AM

The logic looks good.

 

I was going to comment about using pull-up resistors on CLK and IORQ, but then I remembered the scheme again.  With KD enabled, CLK is driven by the 4048 and IORQ is used to drive the circuit.  With KD disabled, IORQ has no effect because the 4048 is in high impedance mode, and therefore CLK can be hooked up directly with no problems.  So it turns out that we're good there.



#64 CharlesMouse OFFLINE  

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Posted Tue May 7, 2019 12:19 PM

The logic looks good.

 

I was going to comment about using pull-up resistors on CLK and IORQ, but then I remembered the scheme again.  With KD enabled, CLK is driven by the 4048 and IORQ is used to drive the circuit.  With KD disabled, IORQ has no effect because the 4048 is in high impedance mode, and therefore CLK can be hooked up directly with no problems.  So it turns out that we're good there.

 

Awesome. :-)

 

Right, gerbers off to Seeed. I really appreciate your invaluable advice on this project, I doubt I would have gotten this far without it. Thank you again.

 

Fingers crossed...

 

PS

Time to see if that AY board of mine actually works before the final parts arrive for the 80 column card arrive & I find out how far from functional that is - will the horror show never end..? :-D






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