Memory expansion into chipram, non destructive

[bni]

Hi folks,

From the product description of the ACA500plus:

"can turn your 512k trapdoor memory expansion into chipram". (ECS Agnus required of course)

Is this a unique feature of the ACA500plus, or is there other accelerators that can do this?

I know this can be accomplished by cutting and soldering, but not interested in that here.

[AmigaHope]

This seems to be a specific feature of the ACA500plus. I've never seen it done by anything else. I don't know how it does it but my guess is it detects when chip memory second bank is accessed on address bus and powers the correct address lines for the ranger memory bus fast enough to get it to respond.

[Jope]

It exploits a feature of the ECS Agnus, basically it always sees the additional 512k from the trapdoor as Chip RAM even if the OS sees it as Ranger Fast.

The ACA500plus performs a realtime address translation so that the CPU thinks the RAM is in the Chip RAM area when in reality it is still at c00000 in hardware. The Agnus doesn't care either way.

[AmigaHope]

Originally Posted by Jope

It exploits a feature of the ECS Agnus, basically it always sees the additional 512k from the trapdoor as Chip RAM even if the OS sees it as Ranger Fast.

The ACA500plus performs a realtime address translation so that the CPU thinks the RAM is in the Chip RAM area when in reality it is still at c00000 in hardware. The Agnus doesn't care either way.

Oh OK, that makes total sense. The address lines are always wired the same way to the Agnus socket and any jumper/trace changes only change the way they connect to the CPU bus. I learned something today!