Dumb question on RAM expansion

[Generale]

Hi there. I'm sitting here looking at an RAS-512K ram expansion card.
There is something bothering me. It's just got the RAM, a clockchip, and some passive components. What's stopping it from being mirrored through the entire memory range? Is it Gary doing this?

[Plaz]

This is a weak answer, because I haven't looked and A500 schematics in ages, but it's the way it's hard-wired to the address buss and gary if I remember any of it well enough. No logic needed if it's wired to the buss properly.

Plaz

[Generale]

So is Gary only good for 1mb?....
Let me see. Well, I know Agnus is lazy and only supports 512k of chip...
Just going to have a look at the schematics to see if that offers a hint.

Thanks for that though.

I was just asking because I know the cpu is good for 16mb, but I just wanted to doctor the ram expansion (it has a dead RAM) and put 1mb on it, but I'm not sure if its possible is all.

[Noster]

Hi,

if I remember right, the ram-expansions for the trapdoor-slot of the A500 that have more than 512KB have an Gary-adapter that wires a single line to a pin of Gary.
The Agnus supports 2MB of RAM (all of them ?), but the early ones support only 512 KB chip-ram and 1.5 MB slow-ram (CPU-only fast-mem, but refreshed by the slow Agnus so this kind of ram has no speed improvement to chip-ram).

Noster

[Doppie1200]

I recall there was a pad on the PCB you could solder. Sort of like a jumer. This mapped the 512k slowram to chipram. But I never thought the OCS chipset could address more than 1MB of chipram. The ECS (A500+) can do 2MB.

[Noster]

Hi,

> But I never thought the OCS chipset could address more than 1MB of chipram.

Not Chip ram, 512 kB Chip ram and 1,5 MB slow mem. The old A2000's have 512 MB Chip and an additional RAM card in the MMU-slot with 0.5 upto 1.5 MB of slow mem. This memory is also refreshed by Agnus, even in the oldest A2000's.

Noster

[RedskullDC]