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Author Topic: Internal memory expansion (Read 122408 times)

Offline Z80System

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Re: Internal memory expansion
« Reply #225 on: 2017.November.04. 11:07:08 »
Quote
The same functions with the same wiring, only in SMD

I count only 8 pin on the red and 10 pin on the green,

and the red one does not seem to have a connector on the right side either ...


That does not seem the same ... where am I wrong ?

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Offline Tutus

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Re: Internal memory expansion
« Reply #226 on: 2017.November.04. 11:37:40 »
I count only 8 pin on the red and 10 pin on the green,

and the red one does not seem to have a connector on the right side either ...


That does not seem the same ... where am I wrong ?

Here is the explanation :)
Only red is available.
http://szergitata.blog.hu/2017/08/18/enterprise_1088kb_ujra_enterprise_1088kb_anew

Offline Z80System

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Re: Internal memory expansion
« Reply #227 on: 2017.November.04. 13:29:41 »
Quote
Here is the explanation :)

Ok, I did not remember, that the pins of the former cable are separated,
so those can be connected (physically) in any order to a board (former or new one) ...
« Last Edit: 2017.November.04. 13:32:49 by Z80System »
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Offline Zozosoft

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Re: Internal memory expansion
« Reply #228 on: 2017.November.21. 10:01:57 »
The same functions with the same wiring, only in SMD
Wiring not same :-(

Now 3 different wiring exist... little crazy :evil:

In this summary colors used from Saint, it is same with the dupont cable colors.

Online gflorez

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Re: Internal memory expansion
« Reply #229 on: 2017.November.21. 10:42:58 »
It is annoying.... I was meaning the same signals there.

Offline Zozosoft

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Re: Internal memory expansion
« Reply #230 on: 2017.November.21. 10:56:05 »
It is annoying....
Yes. But existing "Saint cables" can be modified to universal with cutted dupont headers.
Then just need to care for the proper cable order for the currently installed board. This is why I made this colored table, for a help :-)

Offline Zozosoft

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Re: Internal memory expansion
« Reply #231 on: 2017.November.21. 23:14:47 »
Ooops :oops:
I looked the memory map with the new (red) board, and it is look very crazy :oops:
Then found the suggested wiring on Szörg's page are wrong, two wires need to be replaced.
There is the updated table:


Universal cable which can be used with both Saint and Kotek type boards:
19985-119987-2

With Saint board:
19989-3

With Kotek board:
19991-4

Memorymap of the new red board (Kotek):
19993-5

Offline elmer

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Re: Internal memory expansion
« Reply #232 on: 2020.August.08. 19:42:26 »
Since there doesn't seem to be any option for internal memory expansion available at the moment, I thought that it might be interesting to see what it would take to make a new board.

This thread shows that it might not be *too* difficult to create a simple 512KB expansion board now that smarter people than me have already done the hard work of figuring things out.


Here are a few reference documents that help understand the Z80's memory timing, and using modern components on vintage computers like the Enterprise.

THE Z80 CPU : TIMING
Components Compatibility and Substitution
An Introduction to and Comparison of 74HCT TTL Compatible CMOS Logic

I'm also attaching the datasheet for the SMT SRAM chip that JLCPCB has in stock and available to install on any prototype PCB order.


Since Saint's original 2013 board shows that a 2-chip SRAM solution works (using a GAL for address decoding), and Kotek's board shows that the extra RAM does not need to be decoded in a single block of bank numbers, then what I'm thinking would work is a simple 2-chip board that only uses off-the-shelf components, and would not need any GAL or FPGA programming.

The address decoding would just use a single 74HCT138 set up as ...

/E0: GND
/E1: /MREQ
 E2: /RFSH
 A0: A16
 A1: A20
 A2: A21

The 8 outputs are each valid for a set of 8x64K memory areas:

/Q0: unused
/Q1: unused
/Q2: unused
/Q3: unused
/Q4: unused
/Q5: unused
/Q6: SRAM /CE for banks C0h-C3h,C8h-CBh,D0h-D3h,D8h-DBh,E0h-E3h,E8h-EBh,F0h-F3h,F8h-FBh
/Q7: unused


This would mean that any badly-behaved EP128 software that just assumed that banks F8h-FBh existed would still work.


Does that make sense to those experience people that have gone through this all before over the years?
« Last Edit: 2020.August.08. 22:11:44 by elmer »

Offline Allf

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Re: Internal memory expansion
« Reply #233 on: 2020.August.09. 07:22:48 »
Don't forget - the custom chip are on the board, not only Z80...

Offline dangerman

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Re: Internal memory expansion
« Reply #234 on: 2020.August.09. 12:47:45 »
Hi Elmer. Yes, you definitely want segments F8h-FBh otherwise a lot of software will need patching!

I'm afraid I don't have any experience of ordering SMT boards, but I can confirm that the design for a 512k SRAM expansion is very simple. A couple of years ago I built two expansions myself on strip board - one external and one internal. To my surprise they both work very well even with my bad soldering by hand - tested at 8Mhz and 12Mhz. I didn't even need a 74LS244 buffer on the external expansion.

The internal one used a single programmable logic to give continuous addresses from seg DCh to FBh.
The external one used two standard chips for the same - 74LS141 multiplexer and 74LS20 NAND gates.

But your clever solution uses just one standard chip so is even better.

Happy to help out on this if you have any questions. But it sounds like you're pretty sorted.

Offline dangerman

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Re: Internal memory expansion
« Reply #235 on: 2020.August.09. 22:01:14 »
Also to make the design even easier you can connect the data lines to the SRAM chip in any order.

And the address lines to the RAM chip can also be in any order. The only addresses that can't be swapped around are the ones you're using for /CE.

Does that make sense?

Online gflorez

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Re: Internal memory expansion
« Reply #236 on: 2020.August.10. 01:09:22 »
Also to make the design even easier you can connect the data lines to the SRAM chip in any order.

And the address lines to the RAM chip can also be in any order. The only addresses that can't be swapped around are the ones you're using for /CE.

Don't follow this if you later want to add some FlashRom to your expansion.

-------------------

I am trying to search the gerbers of Saint's Ram expansion(asking him...). Or the ones of the Spanish clone(I still have not contacted  "Quest", the guy that copied it). If not found, don't you think it is easier to not reinvent the wheel? the layout seems very easy to design on Eagle or other similar program. Also, The 512KB or 1MB differences seem easy to add. We also have the GAL formulas kindly given by Saint himself.

The first version from Saint.



This was the Spanish clone, with some differences in the tracks:




Maybe Zozo still has a 1MB Saint's PCB to take some pictures. I better want Saint's permission.

Another option can be the Kotek board. I can also make a batch if the gerbers and CPLD firmware are accessible.  The chips are SMD, but they can still  be soldered at hand with a thin iron.

-------------
Edit: I have found a picture of the second version of Saint's expansion, only upper side and not a good one, due to be black.

« Last Edit: 2020.August.22. 20:30:49 by gflorez »

Offline elmer

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Re: Internal memory expansion
« Reply #237 on: 2020.August.10. 05:07:07 »
Don't follow this if you later want to add some FlashRom to your expansion.

Absolutely! But ... if all that someone is interested in is a simple RAM expansion, then I believe that the suggestion is a good one since it might make routing the traces easier.

Heck, with SzörG's lovely SDcard interface and enough RAM, then modern users might not even see much need to ever add some FlashROM.

It all depends upon what each individual owner wants to do with their Enterprise.


I am trying to search the gerbers of Saint's Ram expansion(asking him...). Or the ones of the Spanish clone(I still have not contacted  "Quest", the guy that copied it). If not found, don't you think it is easier to not reinvent the wheel? the layout seems very easy to design on Eagle or other similar program.

I have absolutely no interest in "reinventing the wheel", nor do I believe that I have the knowledge, experience or skills to somehow invent the "best" internal RAM expansion.

I just want/need an internal RAM expansion for my Enterprise 64, and none seems to be currently available anywhere for me to buy, so I am trying to come up with an *easy* solution that requires minimal soldering or programming, that might be easy and cheap to order, and that hardware-novices could re-order themselves in the future.


When it comes to Saint's lovely design ... the GAL that he used has been obsolete for some time, and they mainly seem to available as "used" units from China. I can find some sellers of NOS parts, but they are 20x the cost of a surface-mount 74HCT138 from JLCPCB.

Other 5V GALs, such as Atmel's ATF16V8B, are still widely available and affordable, but then that would be a change in Saint's design, and I don't know if that would work.

Then, whichever GAL is used, someone has to have the right equipment, and then take the time, to program it.


You, Saint, Kotek and others have far more hardware knowledge than I will ever have, and if you, or someone else produces some boards (of whatever type), then I will probably buy one.

But if not, then is there some reason to avoid the simple 2-chip solution that I am suggesting?

With my limited knowledge, it seems to be almost identical to what both @dangerman and @Zozosoft have already had working, and have shown in other threads.
« Last Edit: 2020.August.10. 06:04:13 by elmer »

Offline elmer

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Re: Internal memory expansion
« Reply #238 on: 2020.August.10. 05:25:55 »
I am trying to search the gerbers of Saint's Ram expansion(asking him...). Or the ones of the Spanish clone(I still have not contacted  "Quest", the guy that copied it).
...
Another option can be the Kotek board. I can also make a batch if the gerbers and CPLD firmware are accessible.  The chips are SMD, but they can still  be soldered at hand with a thin iron.

I forgot to say this before ... thanks! :-)

Offline Dr.OG

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Re: Internal memory expansion
« Reply #239 on: 2020.August.10. 05:58:40 »
I think a simple external RAM expansion connected to the right side port of the computer would be nice as well, without needing to solder and modify the original HW. I know there's the SF3 card, and Pear's Dream Turbo Card, but combined with the SD-card reader connected to the cartridge bay, it would be enough for most users (and much more cheaper I suppose).
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