Leonard Silva de Oliveira schreef:
> Philip wrote:
> >>>Ah, the famous /20-series... Can anybody tell me the difference
> between
> >>the
> >>>VG8235 and the VG8235/20???
> >
> >
> >Well, as far as I know, there is just a little difference between
> these two
> >machines. I used to have the 00-version and that caused many
> problems!!
> >
> >Why, coz the 00 has a hardware memory bug, which makes it IMPOSSIBLE
> to
> play
> >most cracked MEGAroms on disk, although you HAVE the necessary 128kB
> of
> >memory. In the 20-versions, the bug is solved, so with that machine,
> you
> CAN
> >play the cracked games...
> >
> >Greetz,
> >
>
> Does this problem have something to do with the read of the mapper
> registers ?
> I know that some of the japanese memory mappers has no possibility to
> reply the data on the
> mapper registers , making it unreadable. (You get only FF from it when
> reading)
>
No this problem is a pure disign problem , it has something to do with incorrect
timing
> Wich makes allmost all dutch software unusable on it. I was working on
> my own memory mapper
> project using static memory chips.
> I used 8 62256 , 2 74ls138 , 1 74ls30 and 2 74ls670
> The 1st 74ls670 does the mapper mapping and the second holds the
> register value to make the
> mapper ports readable. Without this second one I noticed that programs
> like Moonblaster
> or any other european software wich uses mapper hangs or resets the
> coputer while loading.
>
> By adding the 2nd 74ls670 I got all the tested software running fine
> ....
>
most MSX's (like the NMS8250) use only 1 LS670 but the use a LS125 for readbackthe
design with 2 LS670 (also used in the megamapper from digital KC) will use less
components
(1 IC less) but a more complicated pcb design.
> I´m going to put the schematics online when I finish all my MSX
> hardware projects .....
>
greetings
erik de boer
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