Amiga 500 rev. 6A 1 MB chipRAM + 0,5 or 1 MB fastRAM possible?

[psxphill]

Hello.
Amiga 500 rev. 6A 1 MB chipRAM + 0,5 or 1 MB fastRAM (trapdoor slot) possible? How?

I believe one of the 2mb megachip boards allowed this, because it came with 2mb of chip ram. You didn't jumper gary differently, so the c00000 memory stayed where it was. Instead there was a wire that attached to gary and the megachip board dealt with the addressing.

But it's been many years since I had such a modified a500. IIRC I had 2mb chip + 1.5mb trapdoor.

[psxphill]

I  do not want to buy a RAM expansion card, or rev. 8 motherboard. I want  to use my rev. 6  1 MB chipRAM motherboard + 0,5 MB fastRAM only.
There may not be big disadvantage, if I expand the motherboard onto 1 MB.[/FONT]

I'm pretty sure that doing the standard rev 6 upgrade to 1mb will just stop the trapdoor ram from working. You can probably hack the motherboard and add extra logic that allows both sets of memory to be used, but I haven't heard of anyone ever doing that. So you'll be the first to figure it out.

[psxphill]

I did basically that, except I piggy backed the extra 512K on the chips on the motherboard because I didn't have a trapdoor expansion.

What exactly did you do?

JP3 jumper on rev. 6 motherboard function?
[/B][/FONT]

https://ftp.fau.de/aminet/docs/hard/Trouble.txt

[psxphill]

I think he just wants it as authentic as possible for it's time.

Authentic for an a500 is 0.5mb chip ram.