RAM expansion schematics

eto · 21:20, 28 August 23

Are there any schematics for an external RAM expansion? I'm trying to build an internal RAM expansion with SRAMs but fail with the ideas I had. I thought it might make sense to first check how the external ones work and try to rebuild it - and then see if an internal one could be made.

GUNHED · 00:07, 29 August 23

The Inicrons did an 512 KB battery/accumulator buffered external S-RAM expansion. The data can be accessed probably by using a way back machine of the inicron.de homepage.

eto · 10:31, 29 August 23

Quote from: GUNHED on 00:07, 29 August 23The Inicrons did an 512 KB battery/accumulator buffered external S-RAM expansion. The data can be accessed probably by using a way back machine of the inicron.de homepage.

It's also on the WIKI, but not the schematics. Worst case, I can try to reverse engineer the PCB files.

HAL6128 · 10:58, 29 August 23

Would these brd-files help?

or... here (with schematics):
Nachentwicklung der RAM ROM Box von Inicron für den Amstrad CPC und KCC - Robotrontechnik-Forum

RAM-ROM Box nach Inicron, modifiziert - eb-harwardts Webseite! (jimdofree.com)

eto · 11:36, 29 August 23

Thanks, I have seen this before but the schematics are hard to read. I could contact the author though. BRB files will be the alternative.

thanks for reminding me of this gem ;-)

McArti0 · 14:50, 29 August 23

RAMDIS not use.

eto · 21:45, 31 August 23

Quote from: HAL6128 on 10:58, 29 August 23Would these brd-files help?

finally had a look into it

Unfortunately this is not a RAM expansion and does not help as much as I hoped.

GUNHED · 21:50, 31 August 23

Well, take a look at this then...

McArti0 · 23:13, 31 August 23

Do you want to shadowed rambank 1?

Bryce · 07:19, 01 September 23

Quote from: eto on 11:36, 29 August 23Thanks, I have seen this before but the schematics are hard to read. I could contact the author though. BRB files will be the alternative.

thanks for reminding me of this gem ;-)

Hi Eto,

I think I have an Inicron RAM expansion somewhere. I bought it from someone who built it and said it didn't work, but I don't think I ever tested it or tried to repair it. I can see if I can find it if it's of any use to you?

Bryce.

eto · 08:07, 01 September 23

Quote from: McArti0 on 23:13, 31 August 23Do you want to shadowed rambank 1?

Not sure yet how I will do it. First step is to understand how it works in general.

McArti0 · 09:26, 01 September 23

RAMDISK disables reading from internal memory.
The 6128 disables via PAL nCAS for internal memory.

Now I don't know how to disable Write to internal memory.

eto · 09:41, 01 September 23

Quote from: McArti0 on 09:26, 01 September 23Now I don't know how to disable Write to internal memory.

on the 6128 the PAL logic ensures (as far as I understand) that when RAMDIS is high, CAS0 and CAS1 will never be low.

McArti0 · 10:05, 01 September 23

When RAMDIS is HIGH, CAS0 can be low when /CPU is HIGH (for Screen read by GA).

eto · 10:50, 01 September 23

Quote from: McArti0 on 10:05, 01 September 23When RAMDIS is HIGH, CAS0 can be low when /CPU is HIGH (for Screen read by GA).

true, I was only referring to CPU read/write

McArti0 · 16:05, 01 September 23

https://www.cpcwiki.eu/index.php/RAM_BOX

Here is schem, but ...i dont know...

IanS · 20:11, 01 September 23

https://github.com/revaldinho/cpc_ram_expansion

eto · 06:45, 02 September 23

Quote from: IanS on 20:11, 01 September 23https://github.com/revaldinho/cpc_ram_expansion

Yes, great to build one but there are no schematics.

eto · 06:47, 02 September 23

Thanks everyone for helping out and special thanks to Toto for the work of drawing the schematics.

Prototype PCBs have been ordered :-)

McArti0 · 08:13, 02 September 23

This scheme has major flaws.

Bryce · 11:23, 02 September 23

Quote from: McArti0 on 08:13, 02 September 23This scheme has major flaws.

But you're not going to say what they are??

Bryce.

IanS · 11:37, 02 September 23

Quote from: eto on 06:45, 02 September 23
Quote from: IanS on 20:11, 01 September 23https://github.com/revaldinho/cpc_ram_expansion
Yes, great to build one but there are no schematics.

Not in the usual form, but all the connection information needed is there
https://github.com/revaldinho/cpc_ram_expansion/blob/master/cpc_ram_expansion/pcb/cpc_ram_board_74_v3.00.v

McArti0 · 13:56, 02 September 23

Quote from: Bryce on 2.09.2023, 12:23:11
But you're not going to say what they are?? Bryce.

The transistor is unable to give a high signal to the RAMDIS input.
I think the resistor R1 is for the base of the transistor.
Mayby transistor npn is in other topology? Revers current with GND for colector?

McArti0 · 19:16, 02 September 23

Emiter to PIN RAMDIS, Collector to VCC.

Does anyone want to correct the schematic?

How this work

Bryce · 20:12, 02 September 23

Quote from: McArti0 on 13:56, 02 September 23Quote from: Bryce on 2.09.2023, 12:23:11
But you're not going to say what they are?? Bryce.

The transistor is unable to give a high signal to the RAMDIS input.
I think the resistor R1 is for the base of the transistor.
Mayby transistor npn is in other topology? Revers current with GND for colector?

Or maybe the transistor isn't there to set the RAMDIS, rather to detect if some other expansion is sending a RAMDIS signal so that the expansion RAM also gets disabled?

Bryce.

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RAM expansion schematics