At 04:43 PM 5/20/98 +0400, you wrote:
>> To solve the mapper problem by hardware is very difficult: it's located
>> inside the S1990 MSX-engine.
>> But only software that read mapper ports (which is illegal!) will encounter
>> the problem. Well-written software will work with large mappers on S1990
>> machines.
>
>Can anyone tell me EXACTLY, what document tells that reading mapper ports is
>illegal?
I must admit I don't know the official documents.
I do know that a system with 2 mappers of different sizes will fail in
hardware when the mapper ports are read (both mappers will try to return
different values over the same port at the same time).
I think the fact the hardware can't cope with mapper port reading is enough
reason to call it illegal.
>Yes, I know the problem with poorly designed memory extensions, that don't
support
>reading of their mappers. Did the people try to save money on two extra
chips?
In the case of the S1990, the upper 3 bits are fixed to '1'. So they only
saved a couple of internal transistors by doing this...
Bye,
Maarten
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