Hello! Jim Brain wrote: > It seems like those are the only two options. I looked at the > switchless ROM circuits (basically, a '74 hooked up to RESET as CLK and > RESTORE as D, and I thought a small uC or GAL might also work. Still, it > requires 2 wires. But, then I wondered if one could have the 64 or 128 > act as the uC, and make the ROM switch. I designed something similar few years ago, though it was more complicated beacuse it was meant to be reprogrammable from the C64 side. But some ideas can be reused in a simple project like this. Basically what I did was to remove the SID (as I recall, it is always socketed in a C64), and put it back on a small PCB that goes to the SID socket, but also steals the SID "chip enable", PHI0, R/W and RESET signals and routes them to the second PCB that is inserted into the KERNAL socket. Using these signals, you can create a simple latch which resides somewhere in the SID address space and is used to select the appropriate KERNAL. Upon reset, the latch would be reset to 0 to select the "KERNAL selection KERNAL", which would write the desired KERNAL number to the latch as well as a special bit to disable the latch until next RESET. This is exactly the same thing that our MultiMAX cartridge does - the latch is set to bank 0 upon reset, then the software in bank 0 writes the bank number to the latch, setting also bit 7 which means "disable the latch". You can do that with a 74LS273 plus some simple glue logic - you should have MultiMAX the schematic somewhere as you drew it yourself ;-) Regards, Michau. Message was sent through the cbm-hackers mailing listReceived on 2016-12-22 11:00:02
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