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If you really must put more than 512k on the trapdoor, you really should limit it to 2M. A good expansion will let you map 512k to Chip RAM and the rest to the full 1.5M of the 0x00c00000 portion of the map. When you try to do weird multi-mappings from the trapdoor (i.e. anything not a contiguous block starting from 0x00c00000), that's where the Gary hacks come in. When you start to go into that space you know you are inviting trouble.
Generally the best way to combine expansions is to not use ones that mix address space on different buses. i.e. trapdoor expansions should stick to the trapdoor Slow RAM portion of the memory map, and the CPU-only portion should go on either a CPU piggyback or on the sidecar.
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Hello!
First of all I really enjoyed this nice and well done tech reading (as well the previous post): thanks AmigaHope.
I'm "resurrecting" this thread because I'd like to recover a Datel RAM Master II 1,5MB trapdoor RAM expasion ruined by battery acid.
http://www.bboah.com/index.php?action=artikel&cat=78&id=3578&artlang=enTo map to the system it uses lines coming from a Gary adapter.
If I'll manage to salvage it (and I think so), I'm planning to use it in a A500 with PCB rev.6 with a 1MB Fat Agnus.
I'm wondering if properly configured (I still have to check how to do it - pads, traces mods and so on), this board could give me a standard 1MB Chip RAM and 1MB "Slow" Fast RAM (to be honest I'd like really to have a switch to select 512kB Chip, 1.5MB Slow Fast and 1MB Chip 1MB Slow Fast).
Maybe I have just to try... :-D
BY!
