MagerValp wrote: > Andre> Nevertheless one has to handle the Phi2 delay issue when > Andre> connecting a 6522 -- but any CBM hacker should know that > Andre> already... :-) > > Shame on me for not knowing... :) What's the phi2 delay issue? No problem. The 6522 expects the address and select lines to be valid at the rising edge of Phi2. In the C64, however, the VIC has control over the address lines during Phi2 low. When Phi2 rises, the VIC enables the CPU bus drivers by releasing AEC. Then the CPU address is on the bus, but quite late for the 6522. The normal behavior is to delay the rising edge of Phi2 by one pixel clock with some hardware to fit the 6522 timing. The 6551 (as well as the 6525, 6526, 6521) doesn't seem to suffer from this as it evaluates the address and select lines when Phi2 is high - the 6522 seems to sample them with the rising edge. Andre - mail address may be invalid. Use "fachat AT physik DOT tu-chemnitz DOT de" ------Fight SPAM - join CAUCE http://www.cauce.org------Thanks, spammers... Andre Fachat, Institute of physics, Technische Universität Chemnitz, FRG http://www.tu-chemnitz.de/~fachat
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