I believe the AdRam540 won't work at all on the A500+ because the memory addressing on the board is such that the first 512K on the board will only map to the second 512K of the first 1MB of chip ram (with Fat Agnus 8372A/B) or default to the slow fast mem 512K of unmodified Rev.5, 6A motherboards w/ 8370 Agnus. Since the A500+ has this memory on board (addressed by Agnus 8375) the first 512K of physical memory on the AdRAM can't be recognized. I don't know about the physical addressing of additional memory on the AdRam board but it is probably in the 4MB+/- limit that standard Gary can address via the trapdoor slot. Though it is pin identical, the A500+ trapdoor slot differs from the A500 slot in that it was built to accept a 1MB chip ram card that Fat Agnus 8375 would address at a location unavailable to the slot of the A500. For the same reasons A500 users need a MegaChip or like board in the Agnus PLCC slot itself to add an extra 1MB chip mem afaik.
