On 24/02/2018 04:39, Dr Jefyll wrote: > but the doc I've > seen is unclear as to whether an /actual/ 6509 allows page crossings or > deems them illegal when using $B1 and $91 opcodes for cross-bank accesses. I don't believe there is any timing difference between the 6509 and any nmos 650x/6510/750x/850x etc. They even make that claim on the datasheet http://www.commodore.ca/manuals/6509/6509_01.jpg "The internal process architecture is identical to the Commodore Semiconductor Group 6502 to provide software compatibility". There was certainly no need for them to change it. You can't escape from the zero page when fetching the indirect address, it will wrap and you won't get a penalty. When adding the Y register to the address you can cross a page & there is a penalty. Wrapping from $ffxx to $00xx addresses will still cost you a cycle but it will stay in the same bank. If you have any doubts about general 6502 behaviour then you should be able to resolve them here: http://www.visual6502.org/JSSim/index.html Message was sent through the cbm-hackers mailing listReceived on 2018-02-24 09:00:03
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