> For reading data when the card activates the SBHE-line itself, the above > mechanism can be used as well. But what about writing data??? In that case > it seems we need a temp buffer in D0..7. At first glance I thought I found an even worse scenario: what happens if one starts a DMA from the C64 towards the ISA-bus startong at on odd addres? In that case the above temp buffer doesn't contain any valid data. > SHBE A0 Transfer > 0 0 word > 0 1 byte on D8..15 > 1 0 byte on D0..7 > 1 1 will never occur says the doc *** But then occured to me that there was no problem, see above table. This triggered the following idea: forget about that buffer. In that case the following happens: A0 = 0 : D0..7 is written with data from D0..7 of C64 D8..15 is written with invalid data A0 = 1 : D0..7 stays the same D8..15 is written with data from D0..7 of C64 I don't think this will cause problems with memory but what about I/O: could any harm be done by writing invalid data to D8..15 the first time? Here I merely have the IDE-interface in mind. 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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