Jon De Schrijder schreef:
> Laurens Holst wrote:
> > ...
> > !!! GRUWEL GRUWEL !!!
>
> --> for non-Dutch readers: !!! HORRIFYING HORRIFYING !!!
>
> >
> > Issuing an IN on the mapper-ports is against the MSX-standard!!!
> > NEVER >>IN<< the Mapper-ports. The result is ABSOLUTELY unreliable and
> > machine/mapper-dependant. One computer inverts the result, another sets the
> > highest bits and other computers always return zero or crap.
> >
>
> The debugger in Compass uses IN A,(mapperport) to trace/emulate IN
> instructions of mapperports :)
>
> Jon
Here i have the msx technical databook , micro$oft 5 feb. 1986 rel.6.0
It says on MSX2 memory mapper specification chapter 1 line 4
- The mapping registers are at FCH to FFH of I/O address. The are both read and
write addresses. -
So that rumor is solved , you are allowed to read them.
The only problem is that the unused bit's of the registers can return
unexpected data.( always 1 or 0 or the data you did write to it or maybe crap)
You first have to calculate the amount of memory and the number of used bit's.
If you have done this you can use this information to mask the return data of the
registers.
You also have to take care that some people have more then 1 mapper (however this
is
technically not allowed , but who cares)
Erik.
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