Professor Dredd wrote: > > Okay, it sounds like you're confirming what I > suspected. > > PLA controls which devices the 6510 can see in the map > (RAML/RAMH/ROML/ROMH/IO/CHARGEN). The user/program > CANNOT directly manipulate the PLA. A hardware RESET > signal applied to the PLA (technically -RESET, IIRC) > forces the banking logic of the PLA into the > ROML/ROMH/IO configuration. > The C64 address decode PLA is stupid - its outputs are only dependent on the current inputs. It does not even have a RESET input. It is the fact that the 6510 on-chip port is turned into input mode at RESET that results in the default bank configuration. When the 6510 port is in input mode (=high impendance), the -LORAM, -HIRAM, and -CHAREN pullup resistors will make these signals high. This makes the PLA select the following map: 0000-9FFF: RAM A000-BFFF: BASIC C000-CFFF: RAM D000-DFFF: I/O E000-FFFF: KERNAL -- Christer Palm - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tml.hut.fi.
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