WIP: internal 512K expansion

eto · 15:18, 11 November 24

First stable 464 version...

This one is with 576K in total but no C3 support.

eto · 00:05, 31 December 24

The CPC 6128 version is finished. I didn't find the time to fully document it yet but that should happen over the next few weeks. The final documentation including DIY instructions will be published here: https://www.cpcwiki.eu/index.php/CPC_iRAM

The first fully assembled expansion (the unofficial #1) is available on Ebay. In case you're interested, just search for "CPC iRAM".

Prodatron · 00:15, 31 December 24

Quote from: eto on 00:05, 31 December 24The CPC 6128 version is finished. I didn't find the time to fully document it yet but that should happen over the next few weeks. The final documentation including DIY instructions will be published here: https://www.cpcwiki.eu/index.php/CPC_iRAM.

Fantastic work, thanks a lot for all this!

McArti0 · 08:09, 31 December 24

Now all we need to do is add out hardware patch for CMOS.

... and turbo

Egg Master · 12:52, 03 January 25

@eto I really like a lot the iRAM 640 design, because it looks like something you can buy into the 80s.

@McArti0 People using it already have the NMOS CPU. A great feature will be to unlock the 128K VRAM.

eto · 14:51, 03 January 25

Quote from: Egg Master on 12:52, 03 January 25eto I really like a lot the iRAM 640 design, because it looks like something you can buy into the 80s.

Thanks ;-) To be honest, I think it really only looks like it could have been done. While it does only use "ancient" components I don't think this particular one would have been feasible in the 80s. I had a quick look and I couldn't find anything bigger than 32KB in a 1989 magazine. In 1992 I could at least find a 1Mbit SRAM but no 4MBit version yet. So I'm not sure when even in theory it would have been an option to use in a RAM expansion.

Also the PCB is crammed with lanes. All manually routed and very few vias which seems like doable in the 80s, but I'm not sure if that would have been affordable to achieve for a home computer expansion. In theory it would be possible to make the PCB larger and still fit it into the 6128 but as soon as the ROM or maybe RAM is socketed (e.g. due to a previous repair) there is not enough space to make the PCB even slightly bigger.

However there would have been other options with DRAM.

In the 464/664 you have plenty of space to put in a board with DRAM. The Vortex RAM expansion proofed that but was not compatible with the DK'Tronics standard.

In the 6128 I doubt there is enough space for an add-on board with DRAM. However you could replace the DRAM ICs and add a bit of logic to get 320K or 512K of RAM. Instead of replacing the RAM it would have also been an option to piggy back the RAM and upgrade the CPC to 384K or 576K of RAM (the RAM7 standard was not yet introduced in the 90s, otherwise also 640K would be possible by piggy backing).

When I did the 320/512K upgrade I realised that it requires quite some skills to do the upgrade and it's not really DIY friendly. And that was basically the reason to think about this plug&play upgrade. The goal was no internal soldering, DIY friendly, only cheap, still available through-hole components that can be easily obtained from reliable sellers.

The only compromise I had to do when it comes to how easy this one can be built are the two GALs which need to be programmed and you need to have an Eprom burner or know someone who has one.

Egg Master · 15:07, 03 January 25

Thank you for this full answer. It is appreciated.

You are right, it just looks like. I forget 512K SRAM wasn't available into the 80s. Probably it was more complicated to add internal DRAM instead. At less for 256K. By the way, a final user was not expected to open the computer to connect expansions. Anyway, it ultimately does the illusion for a retro-computer add-on inside the keyboard.

I imagine the 512K can be shared as 256K RAM and 256K Silicon disc?

eto · 15:41, 03 January 25

Quote from: Egg Master on 15:07, 03 January 25I imagine the 512K can be shared as 256K RAM and 256K Silicon disc?

I don't know what the Silicon disc does, sorry.

Prodatron · 15:48, 03 January 25

Quote from: eto on 15:41, 03 January 25
Quote from: Egg Master on 15:07, 03 January 25I imagine the 512K can be shared as 256K RAM and 256K Silicon disc?
I don't know what the Silicon disc does, sorry.

See here:
https://www.cpcwiki.eu/index.php/Dk%27tronics_memory_expansion#256KB_RAM

The "normal" 256K ram expansion uses banks 0-3 (or 1-4 on 6128),
the "silicon disc" 256K ram expansionen uses banks 4-7.

But it's exactly the same, so yes, software which uses the first 256K as CPU ram and the second "silicon" ram as ram disc, will work with iRAM640 as well.

Egg Master · 15:48, 03 January 25

Quote from: eto on 15:41, 03 January 25I don't know what the Silicon disc does, sorry.

Sorry. This is the name given by dk'tronics for the 256K add-on to be used as a RAM disc. (originally with a backup battery)
https://www.cpcwiki.eu/index.php/Dk%27tronics_memory_expansion

@Prodatron Sorry for the double post. Thank you for your answer.

Prodatron · 16:02, 03 January 25

Quote from: Egg Master on 12:52, 03 January 25@eto I really like a lot the iRAM 640 design, because it looks like something you can buy into the 80s.

It was just a little bit larger and required a 464 or 664 (as Eto said)You cannot view this attachment.

(should be the same scale)

Egg Master · 16:26, 03 January 25

Amazing!

Devlin · 16:27, 03 January 25

So, who do I have to kill* to get one of these for my 6128?

*ask very nicely

eto · 16:29, 03 January 25

Quote from: Prodatron on 16:02, 03 January 25It was just a little bit larger and required a 464 or 664 (as Eto said)

Awesome comparison, I love it.

McArti0 · 16:46, 03 January 25

Quote from: Egg Master on 12:52, 03 January 25A great feature will be to unlock the 128K VRAM.

"Realy"?

https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/banked-video-ram/msg231993/#msg231993

But we need one correct. Less time between outs.
Pinball Dreams not start correctly.

GUNHED · 18:09, 03 January 25

Excellent piece of hardware, did already publish the link to the Ebay auction last year in the German forum

Now... all the collectors shall bid what they can to help to compensate the development costs.

BTW.: Would be nice to see the expansion/extension RAM screen of the "OS-Info" tool of FutureOS, just to see which E-RAM I/O is really available. The screens shown before use proprietary numbers only.

dodogildo · 21:28, 03 January 25

Quote from: Prodatron on 16:02, 03 January 25It was just a little bit larger and required a 464 or 664 (as Eto said)

A striking comparison.

Prodatron · 22:28, 03 January 25

Quote from: GUNHED on 18:09, 03 January 25. The screens shown before use proprietary numbers only.

No not at all, SyMon already shows the correct banks

eto · 23:35, 03 January 25

Quote from: GUNHED on 18:09, 03 January 25which E-RAM I/O is really available

SRAM: &7FCx - &7FFF
6128s internal second bank: &7EC1-&7EC8

GUNHED · 00:27, 07 January 25

Quote from: eto on 23:35, 03 January 25
Quote from: GUNHED on 18:09, 03 January 25which E-RAM I/O is really available
SRAM: &7FCx - &7FFF
6128s internal second bank: &7EC1-&7EC8

Thanks, that's what I assumed too. The shown screen was just a bit confusing, because it shows 64 KB Main-RAM and 960 KB expansion RAM (not 1024 KB as I expected). But never mind.

BTW: Congratulations that you sold the i640 on ebay for a decent price. At least a bit of compensation for all the time and efforts you did put into this great project!

eto · 00:55, 07 January 25

Quote from: GUNHED on 00:27, 07 January 25because it shows 64 KB Main-RAM and 960 KB expansion RAM (not 1024 KB

Where do you see 960KB expansion RAM?

eto · 01:16, 07 January 25

Quote from: GUNHED on 00:27, 07 January 25At least a bit of compensation for all the time and efforts you did put into this great project!

I highly appreciate that someone supports it like that. It will be a nice dinner with the family ;-)

But it's definitely not for the money. For the amount of hours and money I put into this I would need to sell at least another 20 for that price just to make minimum wage.

GUNHED · 21:07, 07 January 25

Quote from: eto on 00:55, 07 January 25
Quote from: GUNHED on 00:27, 07 January 25because it shows 64 KB Main-RAM and 960 KB expansion RAM (not 1024 KB
Where do you see 960KB expansion RAM?

The columns are labelled "0" to "F", so 16 columns. First column contains V-RAM, so column "0" is for 64 KB main RAM. Then columns "1" to "F" are 15 columns. 15 x 64 = 960.

eto · 23:33, 07 January 25

Quote from: GUNHED on 21:07, 07 January 25The columns are labelled "0" to "F", so 16 columns. First column contains V-RAM, so column "0" is for 64 KB main RAM. Then columns "1" to "F" are 15 columns. 15 x 64 = 960.

Not related to my RAM expansion, that's SymbOS which supports up to 1MB in total.

GUNHED · 15:20, 08 January 25

Quote from: eto on 23:33, 07 January 25
Quote from: GUNHED on 21:07, 07 January 25The columns are labelled "0" to "F", so 16 columns. First column contains V-RAM, so column "0" is for 64 KB main RAM. Then columns "1" to "F" are 15 columns. 15 x 64 = 960.
Not related to my RAM expansion, that's SymbOS which supports up to 1MB in total.

Exactly! Therefore I did ask in my original post to see that in "OS-Infos", which is more clear to me at least.

I'll attach a picture of the simulated i640 RAM expansion... (btw. Do you sell them? Or is somebody going to build a batch?)

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WIP: internal 512K expansion