Marco Antonio Simon dal Poz <[EMAIL PROTECTED]> wrote:
> > > Is Crazy Train really made by Sony? AFAIK, it's made by Konami.
> >
> > Doesn't the title screen show the name Sony?
We were both right. The title screen shows: "Sony HitBit - Crazytrain
- (c) 1983 Konami". So I guess, that's: made by Konami, 'presented'
by Sony.
Can we rest this silly item now?
> > > I didn't know that 41 42 xx xx can't be used for page 0. Can it be used
> > > for page 3?
> >
> > No, "A", "B", xx, xx only works for pages 1 & 2. Ofcourse, there's
> > nothing preventing you from putting code or data in a ROM in page 3,
> > just a bit difficult to use.
>
> For page 3 the ID code is 41 42 xx xx or 43 44 xx xx?
Alex Wulms explained it quite well: you can put your ROM software in
any page(s) you like. The CSxx-signals are not essential, but just
for the convenience of the cartridge makers. The BIOS only searches
for "AB" in pages 1 and 2. And MSX2 and higher for "CD" in page 0
(subROM).
There's no direct relation between each piece of your ROM software,
and the need to have "AB" or "CD" in some location. This only needs
to be at A place where it is searched, so that your software can
start.
Examples: most 32K ROMs, and megaROMs have "AB" only in page 1. THAT
is found, the init address called, and the code there determines in
what slot it is, selects that slot in page 2 as well, and if needed,
continues with ROM mapper initialisation.
There's no reason either why you couldn't have "AB" codes in pages 0
or 3, either. However the BIOS will only FIND these "AB" codes if
they're in pages 1 or 2. So if you want your software to start, you
should ALSO have this "AB" and init-address in page 1 OR 2 (or
both). If you have "AB" in pages 0 and/or 3 ONLY, and not in pages 1
or 2, then your software won't be found/called.
> [...different cartridge versions...]
>
> Why someone would do it? Is it some kind of unuseful work? But my main
> problem was that I couldn't copy River Raid and Beam Rider cartridges.
Why? Bugfixes? 'Hooks' for easy development/testing? Who cares? They
just are.
> > > Yep, I don't know why ROM doesn't search for cartridges in page 0. Perhaps
> > > this is due to hardware limitations (pins PAGE1, PAGE2, PAGE12 or
> > > something like that).
> >
> > I don't know either. It's no hardware limitation, though.
>
> Perhaps it's only an ENASLT limitation. But ENASLT isn't used while
> cartridges are being reserched over the slots. AFAIK, the startup routines
> use only CALSLT.
It's NO hardware limitation. And it's NO limitation of slotswitch
routines either. The routines like CALSLT, RDSLT, WRSLT, ENASLT etc.
can all work with ALL 4 pages. Only condition is that the stack is
not in the same page you are accessing.
> > > With a SCC cartridge, you will always find certain blocks
> > > in each memory area after reset, otherwise the game might
> > > not re-start each time.
> >
> > You're saying that SCC cartridges have an internal startup
> > circuit, aren't you?
>
> A hardware reset just *resets* these block selections to
> pre-defined values, just like it resets the Z80's program
> counter to 0.
>
> This startup circuit puts only the block 0 in area 4000h or put also
> blocks 1, 2 and 3 in area 6000h, 8000h and A000h?
A hardware reset resets all these 4 memory ranges to blocks 0,1, 2
and 3, simultanious. The same goes for most other Konami megaROMs.
How this is for other megaROMs, I don't know.
> [...megaRAM initialisation...]
> Then your idea is to create a circuit that disables write and disables
> block selecting simultaneously, and enables block selection or write after
> an access on port 8Eh? That's not compatible with the most part of
> Megaroms!
The idea is like this: you add another single bit register. This gets
cleared or set with a hardware reset. In this hardware reset state,
this bit disables both blockswitching and writing to the megaRAM. Any
ACCESS to the megaRAM's I/O-port toggles this bit, re-enabling the
functions AS THEY ARE FOR THE MEGARAM.
So this extra 1-bit register wouldn't get involved in normal megaRAM
control, but only toggle between "disable normal megaRAM functions"
and "enable normal megaRAM functioning".
Ok, it would take some more electronics. That's for the designer to
decide: give it more functions, making it more powerfull or
versatile. Or keep the hardware as simple as possible, limiting its
possibilities.
> > > But how could I load the RAMdisk-software? Don't say by tape!
>> (..)
> But how about with Megaram alone?
What's the use for a megaRAM alone, if it's normal RAM based
(clearing data with power-off)? Don't you always need another drive
to save the data more permanent?
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx MSX Tech Doc page
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