David Heremans wrote:
>
> Laurens Holst wrote:
> > Well since the I/O ports are used and they both have mapped the same
> > ones,
> > they will probably both play the same
>
> >(unless they are used through
> > their
> > BIOS, which however rarely happens, I think only in Basic).
>
> How how how,
> Explain this to me please.
> I think you're wrong. You say yourself that they have the same I/O
> ports. I/O are visible on all busses of the MSX system. The BIOS is a
> Z80 ML prog like any other and it uses the I/O ports to talk to the
> MSX-Music chip. So how can the BIOS make a difference between two chips
> who listen to the same I/O port ????
>
Well ... I think I must say what I know about this topic.
I already had experience with such kind of (let me call this as
"parallelism") configuration. I know that there's two kinds of
MSX music cartridges. The older ones , made by Panasonic which
also have PAC functions and the newer ones based in hacks of internal
MSX Music devices.
It's well known by some MSX advanced programmers that the OPLL inside
the
original Panasonic FM PAC cartridge has a complex controller chip. This
chip
doesn't allow writes to OPLL after a reset on the system until you set a
certain bit at a certain memory address on it's slot. The other one
(hacked
or whatever) does allow writes to OPLL at any moment , since it's
supposed to
be an internal device.
If the FM-PAC (Not FM-PAK) detects that the system already has a
MSX-Music rom
installed it will quit without initializing the bit that allows writes
to the OPLL,
making impossible to produce audio from that cartridge without enabling
that bit
inside an external program. This means that FM PAC will never produce
audio under
"CALL MUSIC" in the MSX Basic of a machine like the MSX Turbo-Rs or
A1WX.
In other hand , if you insert 2 of that "hacked" MSX-Music our one of
that in a computer
that already has an internal MSX music, then both will produce audio ,
or at least you will
get a beautiful crash if the MSX-Music roms are different or conflitant
on the system memory
area. But in a game I'm sure that both units will produce the same
outputs at the same time
because they're also receiving the same clock and address/data bus
signals.
It's the same thing as if you have more than one mapper in your
computer. If you change one of
the mapper ports you will be changing page on all mappers connected to
that computer.
I mean that if you set $FEh port to $f3H you will set all mappers to the
same page , or at least
will change the bits that they do support on their map registers.
I hope this solves the doubt. It's ALWAYS possible to have "parallel"
hardware connected on
the computer, but depending of the kind of hardware it may have weird
effects on the system
software.
I forgot to mention... Since OPLL doesn't have /RD signal it's registers
are write-only.Then
OPLL doesn't supports reading of it's registers. Hardware that do have
readable registers or
possible conflitant firmware (roms) may cause that weird effects that I
did mention a little ago.
Cya MSXers...
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