On 10/09/2014 07:45 AM, Baltissen, GJPAA (Ruud) wrote: > Hallo Julian, >> With some extra logic you could also use an SRAM in your C64 > This has been used to make a C64 run at 2 MHz: 64er, february 1994. If > interested I can upload the magazine (100 MB). Uploading only the > article will take more time because I first have to extract it out of > the PDF. Well, my circuit was simpler, it just replaced the DRAMs with a single SRAM. Besides the 128Kx8 SRAM (only 64KB used), you need a 74HCT573 and a 74HCT32. Also, to get around the VSP-bug, it might help to run _RAS through a few logic gates (a 74LS08 comes to mind) to delay _RAS a bit. > What I wonder about is that the article says to use a 3 MHz 6502. I > would say you would need a 5 MHz one: Well, if you want to stick to NMOS, you can't get more than the 6502B (3 MHz). If you want to use CMOS, back then 4 MHz was max and you got the problem that the illegal opcodes no longer work. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2014-10-09 16:00:08
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