> Correct me if I"m wrong, but the ISA bus's only NMI line, per se, is the > parity error line. As I said before, I develloped a card for the PC where we deliberatly used the NMI line. I don't see why other designers could not have done the same. FYI: handling the NMI interrupt is, just like with the C64, a matter of software. You only have to bend the vector. > Since the c64 wont be generating parity (anyone got a > parity gen circuit?), Here you got me confused. The idea is to connect a PC-card to the C64, not to connect a C64 to a PC ???? > I feel it's best to leave it unhooked so the poor > thing doesnt get an NMI on every bus access. ;) A memory card only will generate a NMI during a read if A) something is wrong with the memory or B) nothing has been written to the address before (parity is not set). A programmer only has to disable the NMI by letting it point to "RTI" for the time he needs to write dummy data to the card and to check if it returns the data in good order. If everything is OK, the NMI-vector can be restored again. (this is the way a PC does it) BUT....... For the moment it is impossible to attach DYNAMIC memorycards to the C64 because there is one vital thing missing: memory refresh. In the PC the 8237 (DMA) disables the CPU so it can supply a memory refresh for all memory including cards. This is where REFRESH/DACK0 is for. Attaching video-cards is no problem as they have there own refresh(= read by video-chip) Groetjes, Ruud http://Ruud.C64.org/ - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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