> Hm, according to the datasheet, the 6500/1 has the ROM located at > $0800-$0FFF. So unless it's wrong, it doesn't make sense to dump any > other pages than 8 to F. Unassigned space will read whatever is on the > bus at that moment (like reading unassigned space in the C64) and the > RAM and I/O contents don't matter. > > Page 0 and 1 are most likely the 64 Bytes RAM mirrored multiple times. It looks like ithe chip decodes addresses like this: -- The top four address bits are disregarded; -- If the next two address bits are not both zero, ROM is selected; -- Otherwise, if bit 7 is 0 RAM is selected; otherwise I/O. ROM uses the low eleven bits for addressing (so you get a mirror 0400..07ff -> 0c00..0fff). RAM uses the low seven bits for addressing (but the top half reads as zeroes; writes presumably are swallowed). I/O uses the low four bits for addressing (so lots of mirrors). In summary: ----00--0xxxxxxx RAM ----00--1---xxxx I/O ----01xxxxxxxxxx ROM ----1-xxxxxxxxxx ROM or perhaps ----00--00xxxxxx RAM ----00--01------ open ----00--1---xxxx I/O ----01xxxxxxxxxx ROM ----1-xxxxxxxxxx ROM Segher Message was sent through the cbm-hackers mailing listReceived on 2014-07-05 19:02:14
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