Amiga 500+ and extra RAM

[orange]

Is Amiga 500+ trapdoor expansion slot compatible with A500 ?
Can I use 1,5Mb slowfast RAM in it ?

[tone007]

My guess would be no, since 500+ trapdoor memory gets added as chip ram, but I've never tried it myself.

[alexh]

No. If it worked at all it would appear as 512Kbytes.

It would never appear as 1.5Mbytes because they only have 1Mbyte of RAM. (A500+ has 1Mbyte Chip RAM on the motherboard and the A501+ and clones add another 1Mbyte to make 2Mbytes Chip RAM)

AFAIR 1.5Mbytes of SlowRAM via the trapdoor on a regular A500 is only possible with a board which uses a Gary Adapter.

[orange]

hm, it seems that expansion (Zydec 1,5M) requires kickstart 1.3
anyway, i got another problem with it now.
it shows only 512K slowfast RAM (in ordinary A500).
could it be its not autoconfig?

[alexh]

Ah, I miss understood your first question. I thought you wanted to use A500+ RAM expansion in an A500 not the other way around.

Hmmm I wonder if it is physically compatible from an address line point of view.

[rkauer]

It is (sort of) compatible. But since the A500 does not have enough address lines to use more than 512kb from the trapdoor memory the remaining RAM will never show up.

 Also the addresses lines that will kept floating will make the Amiga behaviour wobbly, at best.