Nick Coplin wrote: > > I previously check with Ruud, but unfortunately his group didn't have any 7501/8501 CPUs. > > My sample of 6 machines (3 Plus/4 and 3 C16) gives 5.5 dead CPUs (the 0.5 means it works for about 5-10mins and then stops....) > > I'd also be interested in one of these, but I think its pretty rare to find a working sample.... I've heard the failure rate of the original 7501 is much higher than that of the 8501, but still it's not easy to find replacement CPUs. If there's really no spare 8501 on this planet left, the following project might be an option: Use a 6502, a 6522 (for the processor port), a set of two LS244 and one LS245 for the bus tri-state and direction control, a 15 input (and/or/nor/nand, I forgot) gate to select adresses 0/1 and some other minor control logic. This applies for all of the 6510/7501/8500/8501/8502 so far, and the x501 might need an additional gate on the R/W line that is controlled by the "gate in" pin. Though my machines were working fine even with the gate in disconnected, which affected the R/W timing only a little bit. If you add up the costs for a new 6502 and 6522 you'll see immediately why this project isn't an option yet. BTW, do they make new 6502s in PLCC44 casings? I think I know that you can get the 65C02 and 65C22 in this package, but while the 65C22 would be fine, the 65C02 isn't an option due to its different command set. If everything is SMD mounted, it might be possible to make a small adaptor board that is not much larger than the original CPU. Nicolas PS: I have headaches when I think about the recently discovered behaviour of writes/reads to unconnected bits of adresses 0/1. IIRC, the data direction bit is connected, but the data port bit itself is not. Hard to emulate with a 6522 that has both registers in a single chip. - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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