>The cartridge logic necessary for this could be pretty simple: First, it must >boot up the C64 in Ultimax mode (/EXROM=H, /GAME=L), and after a write to the >I/O area (either I/O1 or I/O2) change this to normal EXROM mode (/EXROM=L, /GAME=H). This can be done with a simple LS74 flipflop I guess (/RES and I/O1 >as set/reset inputs, /EXROM and /GAME as outputs Q and /Q). The /ROML and >/ROMH signals must be combined to select the single EPROM, to make the mode >switch possible from inside the ROM, and this can be done with two diodes. I >like this much better than modifying a Supergames cartridge. I used the SuperGames cart as it takes 27xxx EPROMS and had the 74175 latch (and have spares). The upper ROM only has RESET/IRQ/NMI vectors, all directed to $9FE0 The patch at $9FE0 (in the low ROM), just pokes the latch to change memory config, then JMP(8000). I had to split the pad between GAME/EXROM as these are joined by default, and add a wire to connect to the 74175. I also added LEDs (via a 7404) for some additional diagnostics: RED for +5V, YELLOW for RESET high (released), GREEN for ROML (verify that cart is being started/accessed, PLA works), dual colour for Phi2 CLOCK (so as to verify it actually toggles). Nothing published /written up about it yet.... - Nick PLEASE TAKE NOTE: The contents of this email (including any attachments) may be privileged and confidential. Any unauthorised use of the contents is expressly prohibited. If you have received this email in error, please advise us immediately (you can contact us by telephone on +61 8 9441 2311 by reverse charge) and then permanently delete this email together with any attachments. We appreciate your co-operation. Whilst Orbital endeavours to take reasonable care to ensure that this email and any attachments are free from viruses or other defects, Orbital does not represent or warrant that such is explicitly the case (C) 2000: Orbital Engine Company (Australia) PTY LTD and its affiliates Message was sent through the cbm-hackers mailing list
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