] On Thu, 18 Mar 1999, Erik wrote:
]
] > the NMS8220 does have a mapper, and the mapper is 128Kb wide , but only
] > 64Kb of
] > ramis used.
]
] What do you mean with that? It has 64kB, but reacts as 128kB? so:
] out(&Hfe),0:?inp(&Hfe)
] would return &b11111000 in stead of &b11111100? That would be against
] MSX-standard! I must be misunderstanding you, I think...
It would not be. According to the MSX standard, it is not allowed to read the
mapper registers. It is only a courtesy of some manufacturers that they
produced readable mapper registers. If you want to keep track of your mapper
state, you must maintain a copy of the mapper registers in your memory, just
like MSXDOS2 does it.
Actually, there is some history behind this whole story. The original MSX2
technical databook said that it is possible and allowed to read the mapper
registers. But then people realized that you can get problems with multiple
mappers and things like that.For example if one slot contains a 128K mapper
and the other slot contains a 256K mapper. So, the MSX specifications got
changed and from that moment on, it was not allowed anymore to read the
mapper registers.
Kind regards,
Alex Wulms
--
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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