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Author Topic: What internal RAM expansion? (Read 2982 times)

Offline tofro

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What internal RAM expansion?
« on: 2019.September.09. 16:14:48 »
What would be current options for a (moderate, 512k-1M) internal RAM expansion? I understand Saint's board is no longer available.

Thanks, Tobias

Offline Zozosoft

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Re: What internal RAM expansion?
« Reply #1 on: 2019.September.10. 11:00:52 »
I currently don't know any available yet :-(

Online emptiness

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Re: What internal RAM expansion?
« Reply #2 on: 2020.July.19. 15:19:07 »
Are there still no options for RAM expansions (internal or external)? Would be great to have more RAM to play with than standard on the Enterprise 64

Offline dangerman

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Re: What internal RAM expansion?
« Reply #3 on: 2020.July.25. 13:34:00 »
I know that a couple of years ago, Szorg (who makes the SDcard interface) had some.

Or maybe people who've already replaced their internal 128k boards could offer one to you. Hardly anything needs more than 128k.

One day many years from now, I hope to build some more Enterprise expansion hardware myself. But unfortunately, I don't have any time at the moment.:(

Offline Tutus

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Re: What internal RAM expansion?
« Reply #4 on: 2020.July.25. 19:04:19 »
I know that a couple of years ago, Szorg (who makes the SDcard interface) had some.
Or maybe people who've already replaced their internal 128k boards could offer one to you. Hardly anything needs more than 128k.
One day many years from now, I hope to build some more Enterprise expansion hardware myself. But unfortunately, I don't have any time at the moment.:(

We're trying to do something. Unfortunately, there have been so many problems lately (this is understandable). For memory expansion and much more there's SF3. True, not cheap, but the best hardware for Enterprise computer.

Online elmer

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Re: What internal RAM expansion?
« Reply #5 on: 2020.August.06. 19:27:36 »
We're trying to do something. Unfortunately, there have been so many problems lately (this is understandable).

The SF3 is interesting, but it seems to offer far more than I'd personally want.

As someone that recently bought one of the new/almost-new Enterprise 64 machines that have been unearthed in Egypt, I just want some more internal memory, and Szorg's lovely SD card adapter.

From what I have seen posted online, the folks here once got a 512KB expansion board simplified down to using just a 512KBx8 SRAM chip, and a 74LS138 decoder chip, plus some decoupling capacitors.

Does anyone remember seeing a circuit diagram for that anywhere?

If so, then I might be able to persuade a friend to actually produce a board layout that could be ordered from one of the cheap prototyping companies.

These days, it seems pretty easy (and cheap) to get a small batch of unpopulated circuit boards made, so perhaps that would be one solution for those of us that would like to get an internal memory expansion?
« Last Edit: 2020.August.06. 21:25:59 by elmer »

Offline tofro

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Re: What internal RAM expansion?
« Reply #6 on: 2020.August.06. 19:53:49 »
The SF3 is interesting, but it seems to offer far more than I'd personally want.

As someone that recently bought one of the new/almost-new Enterprise 64 machines that have been unearthed in Egypt, I just want some more internal memory, and Szorg's lovely SD card adapter.



Elmer,

I'm pretty much in the same situaton and pretty much looking for something similar - A simple, straightforward internal memory expansion.

In case you get something going, I would definitely be interested and willing to help,

Tobias

Offline ergoGnomik

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Re: What internal RAM expansion?
« Reply #7 on: 2020.August.06. 21:00:24 »
If you are good at electronics and soldering, there's a relatively easy modification to the internal expansion module to upgrade it to 256 kB. There you can find the description. Unfortunately, in Hungarian only.

The most important parts are the linked schematics (1. ábra and 2. ábra; pointing to the top and bottom parts of the very same picture). The top part of the schematic shows the modification on the address multiplexing. The bottom part shows the modification on the DRAM refresh logic.

The instructions go something like this:
Replace the 4164 DRAM ICs with 41256s.
A16, A17 and A18 must be connected to the (top) 74LS151 multiplexer. Its output must be connected to pin 2 of U110.
Disconnect A16 from pin 2 of U112 and connect pin 2 to ground.
Disconnect A17 from pin 1 of U110 and connect pin 1 to +5 Volts.
Disconnect A18 from pin 2 of U110 and connect pin 2 to pin 5 of 74LS151.
Switch SW will disable the expansion if closed and enable it if opened in the contiguous ECh-F7h segment range.
Disconnect pin 12 of U109 from pin 9 of all DRAM ICs.
Connect pin 1 of all (new) DRAM ICs and connect them to pin 12 of U109.
Connect pin 9 of all DRAM ICs to pin 5 of (bottom) 74LS151 multiplexer.
MUX signal can be taken from pin 1 of U108 or U109.
The three TTL ICs can be piggy-backed on components already there on the board but the DRAMs are recommended to be seated in sockets.

Unfortunately, I know next to nothing about electronics, therefore I can't guarantee that my translation makes any sense at all.

Offline geco

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Re: What internal RAM expansion?
« Reply #8 on: 2020.August.06. 22:52:23 »
« Last Edit: 2020.August.06. 23:06:56 by geco »

Offline dangerman

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Re: What internal RAM expansion?
« Reply #9 on: 2020.August.06. 23:20:42 »
Unfortunately if you start with a 64, then there isn't any internal memory expansion board. If you're building a brand new board, then using a single 512k SRAM is much easier than using multiple 41256 chips. :razz:

Offline ergoGnomik

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Re: What internal RAM expansion?
« Reply #10 on: 2020.August.07. 14:15:58 »
Unfortunately if you start with a 64...
Unfortunately, I did not notice that part of the problem. :(

Online elmer

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Re: What internal RAM expansion?
« Reply #11 on: 2020.August.08. 18:33:11 »
Unfortunately, I did not notice that part of the problem. :(

Thank you anyway, your post was really interesting ... but "yes", I'm afraid that us new EP64 owners can't use that solution. ;)


If you're building a brand new board, then using a single 512k SRAM is much easier than using multiple 41256 chips. :razz:

Especially these days, since there are now companies that will cheaply supply and solder SMT (surface mount) components onto a prototype PCB when you have them produce it.

SMT soldering is far beyond my own limited capabilities, but is especially important now that so many modern components are not even available in DIP packaging anymore.

Here is one company that has been recommended to me ... JLPCB.


i do not know if it can help: original internal 64 kb expansion

Yes, thanks!

That schematic clearly shows that the original EP128 designers were limiting the memory board to using each motherboard control/address/data line only once in order to reduce the overall drain/fanout on the motherboard signals.

That's an important consideration to take into account in any new memory board design.


Since this is going to get technical, I'll continue the design and potential manufacturing discussion in the old Internal memory expansion thread.

Online emptiness

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Re: What internal RAM expansion?
« Reply #12 on: 2020.August.16. 23:02:39 »
The SF3 is interesting, but it seems to offer far more than I'd personally want.

As someone that recently bought one of the new/almost-new Enterprise 64 machines that have been unearthed in Egypt, I just want some more internal memory, and Szorg's lovely SD card adapter.

Exactly my situation too. Looks like we bought from the same seller.

Offline Allf

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Re: What internal RAM expansion?
« Reply #13 on: 2020.August.18. 21:46:30 »
I made a 64K internal memory expander (with 2x32K SRAM). Manufacturer's files are based on the original description.

Online elmer

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Re: What internal RAM expansion?
« Reply #14 on: 2020.August.19. 20:13:16 »
I made a 64K internal memory expander (with 2x32K SRAM). Manufacturer's files are based on the original description.

Cool! :-)

I've taken a look at the board layout, and have a question.

Unlike Saint's or Kotek's boards, you're using a 2x5 header on your board for EXP2 instead of a 1x10 header.

Did you solder the cable directly to your expansion PCB, or did you use some kind of 2x5 IDC connector?

How did that work out for you?