> This got me thinking: how does a real SCPU handle access to $01 port? Just my two cents: The 65816 deactivates the 6510 by negating the DMA line. But that can be done in a controlled way, just like the C64 handles the CP/M card. The 6510 runs a program that activates the CP/M and deactivating itself at the same moment. When the Z80 returns control, the 6510 continues the program as if nothing happened. The 65816 can do the same: it gives back the control but makes sure the 6510 will first run a little program that sets or reset certain bits of $00/$01 and then returns control to the 65816 again. This little program can be a little loop of which the 65816 only has to change some bytes to get the wanted results. -- Kind regards / Met vriendelijke groet, Ruud Baltissen www.Baltissen.orgReceived on 2023-04-24 14:00:03
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