Hello, not knowing ANYTHING about the 1551: * On Sat, Nov 12, 2011 at 04:48:57PM +0100 Gerrit Heitsch wrote: > - The I/O-port (full 8 Bit) in the CPU is used for drive control. > There is no SO-pin, suggesting a very different approach to > data transfer between the drive hardware and the controller. > Maybe that's the reason for 2 MHz CPU clock? I would expect it to be the other way around: The 1570/1571 has a SO on the 6502, but it is used in 1541 mode (1 MHz) only. As soon as the 1570/1571 specific mode is used (2 MHz), the SO is not used; instead, the VIA port is polled. I assume that the 2 MHz allows this polling without fear to be too late, while with 1 MHz, this would not be reliable. But, I must admit, I did not do any calculations (yet) to check this assumption. Regards, Spiro. -- Spiro R. Trikaliotis http://opencbm.sf.net/ http://www.trikaliotis.net/ http://www.viceteam.org/ Message was sent through the cbm-hackers mailing listReceived on 2011-11-12 21:00:12
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