] > All mappers use ports FC-FF. More than one mapper can be present in a
] > system. When writing, no problem, all mappers accept the same value. When
] > reading, there is a problem when two mappers want to return different
] > values (for example because they are not equally large).
] >
]
] No problems here. The "smaller" mapper actualy doesn't return the upper bits.
] The "1"s there are caused by +5v pull-up of data bus. If we connect a larger
] mapper the lower bits will be identical and the data bus 1s in the higher bits
The problem with the MSX turbo R is that the pull-up resistors in the engine (S1990)
have a too low resistance, which makes the current that high that even the low-bit
produced by an external large mapper will be pulled up. In theory this can damage both
the external mapper and the S1990. I don't think that Panasonic will produce a new
version of the S1990 to solve that problem. I don't think that Panasonic will produce
anything anymore for MSX. So we will have to live with these problems and work around
them with software routines! Whether we like it or not :-(
Best regards,
Alex
--
Alex Wulms/XelaSoft - MSX of anders NIX - Linux 4 ever
See my homepage for info on the *** XSA *** format
http://www.inter.nl.net/users/A.P.Wulms
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