[Probing for interest] Internal CPC 64K -> 128K expansion (6128 compatible)

[shock__]

Hey there,
I've laid out a PCB for an internal 64K -> 128K memory expansion for the CPC 464/664 which is 6128 compatible and plugs into the CPU socket (usually already socketed). It is based upon the great reverse engineering effort by Porchy and gerald for cloning the PAL16L8 found in CPC6128 computers - all my PCB does is add the additional circuitry.

It's intended as a DIY project - meaning you'd get a bare PCB and would have to collect parts and solder it yourself. I'm currently in the process of writing an assembly manual for various revisions of the boards. Assembling the full expansion in your computer requires programming a GAL, socketing at least 1 more chip (or permanently cutting 2 pins/traces), 'piggybacking' all 8 RAM chips. Apart from the plugin board you'll have to run 8 wires across various points on the board. Overall skill required is low to medium, yet nothing I'd recommend for absolute beginners, but instead as a 2nd or 3rd project if you successfully finished another.

If you're interested, feel free to respond in the thread with the amount you'd take or write me a personal message.
I do intend to order the boards by the 20th of october (10 days from today).

Price for a PCB would be 3.40€ (or less if there's an unexpectedly high interest) + shipping (I'm based in Germany) + optional donation
Price for the other parts required to assemble the expansion should be around 5-10€ depending on where you buy your parts.

As a permanent effort the production files + manual will be released publically under a 'creative commons' license so anyone interested can still produce boards on their own at a later point.

Preview (left variant by OSHPark, right variant in case there's a high interest):

[shock__]

Just ordered 3 prototypes to confirm the layout (turned out I made a mistake in the schematic [wrong pin order] and cleaned up the silkscreen a little).

[Sykobee (Briggsy)]

Interesting. I presume that the 5 pins will need wires to the piggybacked RAM?


Trying to work out if you could put a single 64Kx8 RAM onto this PCB as well...
(or 4, or .

[Bryce]

That wouldn't be possible. The RAM needs to be connected to the CPC via the buffers which are also on the 464 PCB.

Bryce.

[shock__]

Interesting. I presume that the 5 pins will need wires to the piggybacked RAM?


Trying to work out if you could put a single 64Kx8 RAM onto this PCB as well...
(or 4, or .

!CAS0 and !CAS1 go to the RAM. !CAS comes from a lifted pin on the gate array.
The other 5 signals need to be tapped off other ICs (for A14OUT and A15OUT 2 pins need to be lifted and connections wired between the lifted pins and the daughterboard)

[shock__]

PCBs have arrived and are working.
There's a small issue when using sockets for the ICs underneath the Z80 because the stackup gets too high. So you'd either have to solder the 2 ICs directly onto the daughterboard or remove the Z80 socket put in by amstrad (which is of horrible quality anyways) and solder the daughterboard in directly (which is what I did, since it basically serves as a socket as well). If you want to go vanilla 64k again you can remove the GAL and add 3 bridges in the socket or put everything back the way it used to be and use the daughterboard as a socket (on the Z80 every signal is passed through unaltered).

Before:

https://i.imgur.com/E35JrjO.jpg

After:

https://i.imgur.com/CAwGGw7.jpg

Since there was no interest, there won't be a production run (the remaining 2 boards I have are reserved outside of the forum already).
As promised Eagle PCB-layout and schematic are attached. License is CC-BY-SA-NC (https://creativecommons.org/licenses/by-nc-sa/2.0/ - non-commercial means 'no considerable profit' in my understanding, you're of course free to sell boards/parts for the price you paid and take a reasonable fee if you offer pre-assembled ones).
Manual on how to install will follow within the next few days (it should be mostly obvious anyways).